{"id":1347,"date":"2018-08-01T17:08:32","date_gmt":"2018-08-01T17:08:32","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/?post_type=chapter&#038;p=1347"},"modified":"2023-03-16T17:09:42","modified_gmt":"2023-03-16T17:09:42","slug":"lewis-structures-from-che151","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/chapter\/lewis-structures-from-che151\/","title":{"raw":"6.2 Lewis Structures","rendered":"6.2 Lewis Structures"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Write Lewis symbols for neutral atoms and ions<\/li>\r\n \t<li>Draw Lewis structures depicting the bonding in simple molecules<\/li>\r\n<\/ul>\r\n<\/div>\r\nWe have discussed the various types of bonds that form between atoms and\/or ions. In all cases, these bonds involve the sharing or transfer of valence shell electrons between atoms. In this section, we will explore the typical method for depicting valence shell electrons and chemical bonds, namely Lewis symbols and Lewis structures.\r\n<h2>Lewis Symbols<\/h2>\r\nWe use Lewis symbols to describe valence electron configurations of atoms and monatomic ions. A <strong>Lewis symbol <\/strong>consists of an elemental symbol surrounded by one dot for each of its valence electrons:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211351\/CNX_Chem_07_03_Lewisstruct1_img1.jpg\" alt=\"A Lewis structure of calcium is shown. A lone pair of electrons are shown to the right of the symbol.\" width=\"325\" height=\"34\" \/>\r\n\r\nFigure 1 shows the Lewis symbols for the elements of the third period of the periodic table.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"881\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211352\/CNX_Chem_07_03_3rowLewis1.jpg\" alt=\"A table is shown that has three columns and nine rows. The header row reads \u201cAtoms,\u201d \u201cElectronic Configuration,\u201d and \u201cLewis Symbol.\u201d The first column contains the words \u201csodium,\u201d \u201cmagnesium,\u201d \u201caluminum,\u201d \u201csilicon,\u201d \u201cphosphorus,\u201d \u201csulfur,\u201d \u201cchlorine,\u201d and \u201cargon.\u201d The second column contains the symbols and numbers \u201c[ N e ] 3 s superscript 2,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 1,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 2,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 3,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 4,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 5,\u201d and \u201c[ N e ] 3 s superscript 2, 3 p superscript 6.\u201d The third column contains Lewis structures for N a with one dot, M g with two dots, A l with three dots, Si with four dots, P with five dots, S with six dots, C l with seven dots, and A r with eight dots.\" width=\"881\" height=\"416\" \/> Figure 1. Lewis symbols illustrating the number of valence electrons for each element in the third period of the periodic table.[\/caption]Lewis symbols can also be used to illustrate the formation of cations from atoms, as shown here for sodium and calcium:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211353\/CNX_Chem_07_03_NaCa_img1.jpg\" alt=\"Two diagrams are shown. The left diagram shows a Lewis dot structure of sodium with one dot, then a right-facing arrow leading to a sodium symbol with a superscripted plus sign, a plus sign, and the letter \u201ce\u201d with a superscripted negative sign. The terms below this diagram read \u201cSodium atom\u201d and \u201cSodium cation.\u201d The right diagram shows a Lewis dot structure of calcium with two dots, then a right-facing arrow leading to a calcium symbol with a superscripted two and a plus sign, a plus sign, and the value \u201c2e\u201d with a superscripted negative sign. The terms below this diagram read \u201cCalcium atom\u201d and \u201cCalcium cation.\u201d\" width=\"885\" height=\"81\" \/>\r\n\r\nLikewise, they can be used to show the formation of anions from atoms, as shown below for chlorine and sulfur:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211355\/CNX_Chem_07_03_ClS_img1.jpg\" alt=\"Two diagrams are shown. The left diagram shows a Lewis dot structure of chlorine with seven dots and the letter \u201ce\u201d with a superscripted negative sign, then a right-facing arrow leading to a chlorine symbol with eight dots and a superscripted negative sign. The terms below this diagram read, \u201cChlorine atom,\u201d and, \u201cChlorine anion.\u201d The right diagram shows a Lewis dot structure of sulfur with six dots and the symbol \u201c2e\u201d with a superscripted negative sign, then a right-facing arrow leading to a sulfur symbol with eight dots and a superscripted two and negative sign. The terms below this diagram read, \u201cSulfur atom,\u201d and, \u201cSulfur anion.\u201d\" width=\"883\" height=\"89\" \/>\r\n\r\nFigure 2 demonstrates the use of Lewis symbols to show the transfer of electrons during the formation of ionic compounds.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"884\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211357\/CNX_Chem_07_03_IonLewis1.jpg\" alt=\"A table is shown with four rows. The header row reads \u201cMetal,\u201d \u201cNonmetal,\u201d and \u201cIonic Compound.\u201d The second row shows the Lewis structures of a reaction. A sodium symbol with one dot, a plus sign, and a chlorine symbol with seven dots lie to the left of a right-facing arrow. To the right of the arrow a sodium symbol with a superscripted plus sign is drawn next to a chlorine symbol with eight dots surrounded by brackets with a superscripted negative sign. One of the dots on the C l atom is red. The terms \u201csodium atom,\u201d \u201cchlorine atom,\u201d and \u201csodium chloride ( sodium ion and chloride ion )\u201d are written under the reaction. The third row shows the Lewis structures of a reaction. A magnesium symbol with two red dots, a plus sign, and an oxygen symbol with six dots lie to the left of a right-facing arrow. To the right of the arrow a magnesium symbol with a superscripted two and a plus sign is drawn next to an oxygen symbol with eight dots, two of which are red, surrounded by brackets with a superscripted two a and a negative sign. The terms \u201cmagnesium atom,\u201d \u201coxygen atom,\u201d and \u201cmagnesium oxide ( magnesium ion and oxide ion )\u201d are written under the reaction. The fourth row shows the Lewis structures of a reaction. A calcium symbol with two red dots, a plus sign, and a fluorine symbol with a coefficient of two and seven dots lie to the left of a right-facing arrow. To the right of the arrow a calcium symbol with a superscripted two and a plus sign is drawn next to a fluorine symbol with eight dots, one of which is red, surrounded by brackets with a superscripted negative sign and a subscripted two. The terms \u201ccalcium atom,\u201d \u201cfluorine atoms,\u201d and \u201ccalcium fluoride ( calcium ion and two fluoride ions )\u201d are written under the reaction.\" width=\"884\" height=\"457\" \/> Figure 2. Cations are formed when atoms lose electrons, represented by fewer Lewis dots, whereas anions are formed by atoms gaining electrons. The total number of electrons does not change.[\/caption]\r\n<h2>Lewis Structures<\/h2>\r\nWe also use Lewis symbols to indicate the formation of covalent bonds, which are shown in<strong> Lewis structures<\/strong>, drawings that describe the bonding in molecules and polyatomic ions. For example, when two chlorine atoms form a chlorine molecule, they share one pair of electrons:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211358\/CNX_Chem_07_03_C12dot_img1.jpg\" alt=\"A Lewis dot diagram shows a reaction. Two chlorine symbols, each surrounded by seven dots are separated by a plus sign. The dots on the first atom are all black and the dots on the second atom are all read. The phrase, \u201cChlorine atoms\u201d is written below. A right-facing arrow points to two chlorine symbols, each with six dots surrounding their outer edges and a shared pair of dots in between. One of the shared dots is black and one is red. The phrase, \u201cChlorine molecule\u201d is written below.\" \/>\r\n\r\nThe Lewis structure indicates that each Cl atom has three pairs of electrons that are not used in bonding (called <strong>lone pairs<\/strong>) and one shared pair of electrons (written between the atoms). A dash (or line) is sometimes used to indicate a shared pair of electrons:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211400\/CNX_Chem_07_03_Cl2dash_img1.jpg\" alt=\"Two Lewis structures are shown. The left-hand structure shows two H atoms connected by a single bond. The right-hand structure shows two C l atoms connected by a single bond and each surrounded by six dots.\" \/>\r\n\r\nA single shared pair of electrons is called a <strong>single bond<\/strong>. Each Cl atom interacts with eight valence electrons: the six in the lone pairs and the two in the single bond.\r\n<h3>The Octet Rule<\/h3>\r\nThe other halogen molecules (F<sub>2<\/sub>, Br<sub>2<\/sub>, I<sub>2<\/sub>, and At<sub>2<\/sub>) form bonds like those in the chlorine molecule: one single bond between atoms and three lone pairs of electrons per atom. This allows each halogen atom to have a noble gas electron configuration. The tendency of main group atoms to form enough bonds to obtain eight valence electrons is known as the <strong>octet rule<\/strong>.\r\n\r\nThe number of bonds that an atom can form can often be predicted from the number of electrons needed to reach an octet (eight valence electrons); this is especially true of the nonmetals of the second period of the periodic table (C, N, O, and F). For example, each atom of a group 14 element has four electrons in its outermost shell and therefore requires four more electrons to reach an octet. These four electrons can be gained by forming four covalent bonds, as illustrated here for carbon in CCl<sub>4<\/sub> (carbon tetrachloride) and silicon in SiH<sub>4<\/sub> (silane). Because hydrogen only needs two electrons to fill its valence shell, it is an exception to the octet rule. The transition elements and inner transition elements also do not follow the octet rule:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211401\/CNX_Chem_07_03_XY4struc_img1.jpg\" alt=\"Two sets of Lewis dot structures are shown. The left structures depict five C l symbols in a cross shape with eight dots around each, the word \u201cor\u201d and the same five C l symbols, connected by four single bonds in a cross shape. The name \u201cCarbon tetrachloride\u201d is written below the structure. The right hand structures show a S i symbol, surrounded by eight dots and four H symbols in a cross shape. The word \u201cor\u201d separates this from an S i symbol with four single bonds connecting the four H symbols in a cross shape. The name \u201cSilane\u201d is written below these diagrams.\" \/>\r\n\r\nGroup 15 elements such as nitrogen have five valence electrons in the atomic Lewis symbol: one lone pair and three unpaired electrons. To obtain an octet, these atoms form three covalent bonds, as in NH<sub>3<\/sub> (ammonia). Oxygen and other atoms in group 16 obtain an octet by forming two covalent bonds:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211402\/CNX_Chem_07_03_numbonds_img1.jpg\" alt=\"Three Lewis structures labeled, \u201cAmmonia,\u201d \u201cWater,\u201d and \u201cHydrogen fluoride\u201d are shown. The left structure shows a nitrogen atom with a lone pair of electrons and single bonded to three hydrogen atoms. The middle structure shows an oxygen atom with two lone pairs of electrons and two singly-bonded hydrogen atoms. The right structure shows a hydrogen atom single bonded to a fluorine atom that has three lone pairs of electrons.\" \/>\r\n<h3>Double and Triple Bonds<\/h3>\r\nAs previously mentioned, when a pair of atoms shares one pair of electrons, we call this a single bond. However, a pair of atoms may need to share more than one pair of electrons in order to achieve the requisite octet. A <strong>double bond <\/strong>forms when two pairs of electrons are shared between a pair of atoms, as between the carbon and oxygen atoms in CH<sub>2<\/sub>O (formaldehyde) and between the two carbon atoms in C<sub>2<\/sub>H<sub>4<\/sub> (ethylene):<img class=\"aligncenter wp-image-6464 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/915\/2015\/04\/20153809\/CNX_Chem_07_03_DoubleBond_img1_rev1.jpg\" alt=\"Two pairs of Lewis structures are shown. The left pair of structures shows a carbon atom forming single bonds to two hydrogen atoms. There are four electrons between the C atom and an O atom. The O atom also has two pairs of dots. The word \u201cor\u201d separates this structure from the same diagram, except this time there is a double bond between the C atom and O atom. The name, \u201cFormaldehyde\u201d is written below these structures. On the the left are two C atoms with four dots in between them and each forming single bonds to two H atoms. The word \u201cor\u201d lies to the left of the second structure, which is the same except that the C atoms form double bonds with one another. The name, \u201cEthylene\u201d is written below these structures.\" width=\"790\" height=\"182\" \/>\r\n\r\nA <strong>triple bond<\/strong> forms when three electron pairs are shared by a pair of atoms, as in nitrogen gas (N<sub>2<\/sub>):\r\n\r\n<img class=\"aligncenter wp-image-1715 \" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14032405\/nitrogen-gas.jpg\" alt=\"\" width=\"135\" height=\"41\" \/>\r\n<h2>Writing Lewis Structures with the Octet Rule<\/h2>\r\nFor very simple molecules and molecular ions, we can write the Lewis structures by merely pairing up the unpaired electrons on the constituent atoms. See these examples:\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211406\/CNX_Chem_07_03_Unprelec_img1.jpg\" alt=\"Three reactions are shown with Lewis dot diagrams. The first shows a hydrogen with one red dot, a plus sign and a bromine with seven dots, one of which is red, connected by a right-facing arrow to a hydrogen and bromine with a pair of red dots in between them. There are also three lone pairs on the bromine. The second reaction shows a hydrogen with a coefficient of two and one red dot, a plus sign, and a sulfur atom with six dots, two of which are red, connected by a right facing arrow to two hydrogen atoms and one sulfur atom. There are two red dots in between the two hydrogen atoms and the sulfur atom. Both pairs of these dots are red. The sulfur atom also has two lone pairs of dots. The third reaction shows two nitrogen atoms each with five dots, three of which are red, separated by a plus sign, and connected by a right-facing arrow to two nitrogen atoms with six red electron dots in between one another. Each nitrogen atom also has one lone pair of electrons.\" \/>\r\n\r\nFor more complicated molecules and molecular ions, it is helpful to follow the step-by-step procedure outlined here:\r\n<ol>\r\n \t<li>Determine the total number of valence (outer shell) electrons.<\/li>\r\n \t<li>Draw a skeleton structure of the molecule, arranging the atoms around a central atom. (Generally, the atom that can form more bonding pairs will be the central element, or as we will learn later, the least electronegative element will be the central atom.) Connect each atom to the central atom with a single bond (one electron pair).<\/li>\r\n \t<li>Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.<\/li>\r\n \t<li>Place all remaining electrons on the central atom.<\/li>\r\n \t<li>Rearrange the electrons of the outer atoms to make multiple bonds with the central atom in order to obtain octets wherever possible.<\/li>\r\n<\/ol>\r\nLet us determine the Lewis structure of PBr<sub>3<\/sub> using the steps above:\r\n<ul>\r\n \t<li>Step 1: Determine the total number of valence (outer shell) electrons.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: center;\">[latex]\\large \\begin{array}{l}\\\\ \\phantom{\\rule{0.8em}{0ex}}{\\text{PBr}}_{3}\\\\ \\phantom{\\rule{0.8em}{0ex}}\\text{P: 5 valence electrons\/atom}\\times \\text{1 atom}=5\\\\ \\underline{+\\text{Br: 7 valence electron\/atom}\\times \\text{3 atoms}=21}\\\\ \\\\ \\phantom{\\rule{15.95em}{0ex}}=\\text{26 valence electrons}\\end{array}[\/latex]<\/p>\r\n\r\n<ul>\r\n \t<li>Step 2: Draw a skeleton structure of the molecule, arranging the atoms around a central atom. (Generally, the least electronegative element should be placed in the center.) Connect each atom to the central atom with a single bond (one electron pair).<\/li>\r\n<\/ul>\r\n<p style=\"text-align: center;\"><img class=\"aligncenter wp-image-1507 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/19194359\/PBr3.jpg\" alt=\"Lewis diagram of PBr3 is shown. The one phosphorus single boned to three bromine atoms. \" width=\"228\" height=\"128\" \/><\/p>\r\n\r\n<ul>\r\n \t<li>Step 3: Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.<\/li>\r\n \t<li><img class=\"aligncenter size-full wp-image-1508\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/19195038\/PBr3Lewis.jpg\" alt=\"Lewis doagram of PBr3. A single atom of phosphorus bonded to three bromine atoms. Each bromine atom has three lone pairs.\" width=\"254\" height=\"162\" \/>Step 4: Place all remaining electrons on the central atom.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: center;\"><img class=\"aligncenter size-full wp-image-1510\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/19200010\/PBr3Lewisstructure.jpg\" alt=\"Lewis structure for PBr3 is shown. All atoms have octets. Phorsphorus is singly bonded to three bromine's. The phorphorus atom has one lone pair, while each bromine has three lone pairs.\" width=\"250\" height=\"157\" \/><\/p>\r\n&nbsp;\r\n<p style=\"padding-left: 30px;\">Note: Step 5: Is not needed since all atoms have an octet.<\/p>\r\n&nbsp;\r\n\r\nLet us determine the Lewis structure of CH<sub>2<\/sub>O.\r\n<ul>\r\n \t<li>Step 1: Determine the total number of valence (outer shell) electrons.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: center;\">[latex]\\large \\begin{array}{l}\\\\ \\phantom{\\rule{0.8em}{0ex}}{\\text{H}_{2}}\\text{CO}\\\\ \\phantom{\\rule{0.8em}{0ex}}\\text{H: 1 valence electron\/atom}\\times \\text{2 atom}=2\\\\\\text{C: 4 valence electrons\/atom}\\times \\text{1 atom}=4\\\\ \\underline{+\\text{O: 6 valence electrons\/atom}\\times \\text{1 atoms}=6}\\\\ \\\\ \\phantom{\\rule{15.95em}{0ex}}=\\text{12 valence electrons}\\end{array}[\/latex]<\/p>\r\n\r\n<ul>\r\n \t<li>Step 2: Draw a skeleton structure of the molecule, arranging the atoms around a central atom. (Generally, the least electronegative element should be placed in the center.) Connect each atom to the central atom with a single bond (one electron pair).<\/li>\r\n<\/ul>\r\n<p style=\"text-align: center;\"><img class=\"aligncenter size-full wp-image-1512\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20021300\/H2COskeletal.jpg\" alt=\"Lewis diagram shown. Central atom is carbon, bonded to one oxygen and two hydrogens.\" width=\"213\" height=\"125\" \/><\/p>\r\n\r\n<ul>\r\n \t<li>Step 3: Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: center;\"><img class=\"aligncenter size-full wp-image-1513\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20021728\/H2COlonepairs.jpg\" alt=\"\" width=\"207\" height=\"131\" \/><\/p>\r\n\r\n<ul>\r\n \t<li>Step 4: Not needed, since all electrons have been placed.\u00a0 However, carbon does not have an octet,<\/li>\r\n \t<li>Step 5: Rearrange the electrons of the outer atoms to make multiple bonds with the central atom in order to obtain octets wherever possible.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: center;\"><img class=\"aligncenter size-full wp-image-1514\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20022000\/H2COfinal.jpg\" alt=\"\" width=\"203\" height=\"119\" \/><\/p>\r\n\r\n<div class=\"textbox examples\">\r\n<h3>Example 1: Writing Lewis Structures<\/h3>\r\nNASA\u2019s Cassini-Huygens mission detected a large cloud of toxic hydrogen cyanide (HCN) on Titan, one of Saturn\u2019s moons. What are the Lewis structures of these molecules?\r\n\r\n[reveal-answer q=\"131813\"]Show Step 1[\/reveal-answer]\r\n\r\n[hidden-answer a=\"131813\"]\r\n\r\n<em><strong>Step 1:<\/strong> Calculate the number of valence electrons.<\/em>\r\nHCN: (1 \u00d7 1) + (4 \u00d7 1) + (5 \u00d7 1) = 10\r\n\r\n[\/hidden-answer]\r\n\r\n[reveal-answer q=\"131814\"]Show Step 2[\/reveal-answer]\r\n\r\n[hidden-answer a=\"131814\"]\r\n\r\n<em><strong>Step 2.<\/strong> Draw a skeleton and connect the atoms with single bonds.<\/em> Remember that H is never a central atom:\r\n\r\n<img class=\"aligncenter size-full wp-image-1717\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14032949\/HCN.jpg\" alt=\"\" width=\"167\" height=\"107\" \/>\r\n\r\n[\/hidden-answer]\r\n\r\n[reveal-answer q=\"131815\"]Show Step 3[\/reveal-answer]\r\n\r\n[hidden-answer a=\"131815\"]\r\n\r\n<em><strong>Step 3<\/strong>: Where needed, distribute electrons to the terminal atoms:<\/em>\r\n\r\nHCN: six electrons placed on N\r\n\r\n<img class=\"aligncenter size-full wp-image-1716\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14032831\/HCN1.jpg\" alt=\"\" width=\"177\" height=\"111\" \/>\r\n\r\n[\/hidden-answer]\r\n\r\n[reveal-answer q=\"131816\"]Show Step 4[\/reveal-answer]\r\n\r\n[hidden-answer a=\"131816\"]\r\n\r\n<em><strong>Step 4<\/strong>: Where needed, place remaining electrons on the central atom:<\/em>\r\n\r\n<img class=\"aligncenter size-full wp-image-1718\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14033129\/HCN2.jpg\" alt=\"\" width=\"181\" height=\"98\" \/>HCN: no electrons remain\r\n\r\n[\/hidden-answer]\r\n\r\n[reveal-answer q=\"131817\"]Show Step 5[\/reveal-answer]\r\n\r\n[hidden-answer a=\"131817\"]\r\n\r\n<em><strong>Step 5<\/strong>: Where needed, rearrange electrons to form multiple bonds in order to obtain an octet on each atom:<\/em>\r\nHCN: form two more C\u2013N bonds\r\n<img class=\"aligncenter size-full wp-image-1719\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14033229\/HCN3.jpg\" alt=\"\" width=\"174\" height=\"131\" \/>\r\n\r\n[\/hidden-answer]\r\n\r\n<strong>Check Your Learning<\/strong>\r\n\r\nCarbon dioxide, CO<sub>2<\/sub>, is a product of the combustion of fossil fuels. CO<sub>2<\/sub> has been implicated in global climate change. What is the Lewis structure of CO<sub>2<\/sub>?\r\n[reveal-answer q=\"13181\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"13181\"]\r\n\r\n<img class=\"aligncenter wp-image-1515\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20022859\/CO2.jpg\" alt=\"\" width=\"183\" height=\"53\" \/>\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Key Concepts and Summary<\/h3>\r\nValence electronic structures can be visualized by drawing Lewis symbols (for atoms and monatomic ions) and Lewis structures (for molecules and polyatomic ions). Lone pairs, unpaired electrons, and single, double, or triple bonds are used to indicate where the valence electrons are located around each atom in a Lewis structure. Most structures\u2014especially those containing second row elements\u2014obey the octet rule, in which every atom (except H) is surrounded by eight electrons. Exceptions to the octet rule occur for odd-electron molecules (free radicals), electron-deficient molecules, and hypervalent molecules.\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Exercises<\/h3>\r\n<ol>\r\n \t<li>Write the Lewis symbols for each of the following ions:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>As<sup>3\u2013 <\/sup><\/li>\r\n \t<li>I<sup>\u2013 <\/sup><\/li>\r\n \t<li>Be<sup>2+ <\/sup><\/li>\r\n \t<li>O<sup>2\u2013 <\/sup><\/li>\r\n \t<li>Ga<sup>3+ <\/sup><\/li>\r\n \t<li>Li<sup>+ <\/sup><\/li>\r\n \t<li>N<sup>3\u2013<\/sup><\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>Many monatomic ions are found in seawater, including the ions formed from the following list of elements. Write the Lewis symbols for the monatomic ions formed from the following elements:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>Cl<\/li>\r\n \t<li>Na<\/li>\r\n \t<li>Mg<\/li>\r\n \t<li>Ca<\/li>\r\n \t<li>K<\/li>\r\n \t<li>Br<\/li>\r\n \t<li>Sr<\/li>\r\n \t<li>F<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>Write the Lewis symbols of the ions in each of the following ionic compounds and the Lewis symbols of the atom from which they are formed:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>MgS<\/li>\r\n \t<li>Al<sub>2<\/sub>O<sub>3 <\/sub><\/li>\r\n \t<li>GaCl<sub>3 <\/sub><\/li>\r\n \t<li>K<sub>2<\/sub>O<\/li>\r\n \t<li>Li<sub>3<\/sub>N<\/li>\r\n \t<li>KF<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>In the Lewis structures listed below, M and X represent various elements in the third period of the periodic table. Write the formula of each compound using the chemical symbols of each element:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211453\/CNX_Chem_07_03_MXLewisa_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted two positive sign. The right shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign outside of the brackets.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211454\/CNX_Chem_07_03_MXLewisb_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted three positive sign. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted negative sign and a subscripted three both outside of the brackets.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211455\/CNX_Chem_07_03_MXLewisc_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted positive sign and a subscripted two outside of the brackets. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign outside of the brackets.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211456\/CNX_Chem_07_03_MXLewisd_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted three positive sign and a subscripted two outside of the brackets. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign and subscripted three both outside of the brackets.\" \/><\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>Write the Lewis structure for the diatomic molecule P<sub>2<\/sub>, an unstable form of phosphorus found in high-temperature phosphorus vapor.<\/li>\r\n \t<li>Write Lewis structures for the following:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>H<sub>2 <\/sub><\/li>\r\n \t<li>HBr<\/li>\r\n \t<li>PCl<sub>3 <\/sub><\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>Write Lewis structures for the following:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>O<sub>2 <\/sub><\/li>\r\n \t<li>H<sub>2<\/sub>CO<\/li>\r\n \t<li>AsF<sub>3 <\/sub><\/li>\r\n \t<li>SiCl<sub>4 <\/sub><\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"152254\"]Selected Answers[\/reveal-answer]\r\n[hidden-answer a=\"152254\"]\r\n1. The Lewis symbol for each ion is as follows:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>eight electrons:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211436\/CNX_Chem_07_03_Question1a_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for arsenic, A s, surrounded by eight dots and a superscripted three negative sign.\" \/><\/li>\r\n \t<li>eight electrons:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211437\/CNX_Chem_07_03_Question1b_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for iodine, I, surrounded by eight dots and a superscripted negative sign.\" \/><\/li>\r\n \t<li>no electrons Be<sup>2+<\/sup><\/li>\r\n \t<li>eight electrons:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211438\/CNX_Chem_07_03_Question1d_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for oxygen, O, surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\r\n \t<li>no electrons Ga<sup>3+<\/sup><\/li>\r\n \t<li>no electrons Li<sup>+<\/sup><\/li>\r\n \t<li>eight electrons:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211439\/CNX_Chem_07_03_Question1g_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for nitrogen, N, surrounded by eight dots and a superscripted three negative sign.\" \/><\/li>\r\n<\/ol>\r\n3. The Lewis symbols are as follows:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211445\/CNX_Chem_07_03_Exercise3a_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol M g with a superscripted two positive sign while the right shows the symbol S surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211446\/CNX_Chem_07_03_Exercise3b_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol A l with a superscripted three positive sign while the right shows the symbol O surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211447\/CNX_Chem_07_03_Exercise3c_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol G a with a superscripted three positive sign while the right shows the symbol C l surrounded by eight dots and a superscripted negative sign.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211448\/CNX_Chem_07_03_Exercise3d_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol K with a superscripted positive sign while the right shows the symbol O surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211449\/CNX_Chem_07_03_Exercise3e_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol L i with a superscripted positive sign while the right shows the symbol N surrounded by eight dots and a superscripted three negative sign.\" \/><\/li>\r\n \t<li><img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211452\/CNX_Chem_07_03_Exercise3f_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol K with a superscripted positive sign while the right shows the symbol F surrounded by eight dots and a superscripted negative sign.\" \/><\/li>\r\n<\/ol>\r\n5. <img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211457\/CNX_Chem_07_03_Question5_img1.jpg\" alt=\"A Lewis diagram shows two phosphorus atoms triple bonded together each with one lone electron pair.\" \/>\r\n\r\n7. The Lewis structures are as follows:\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>O<sub>2<\/sub>:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211507\/CNX_Chem_07_03_Question7a_img1.jpg\" alt=\"A Lewis structure shows two oxygen atoms double bonded together, and each has two lone pairs of electrons.\" \/>\r\nIn this case, the Lewis structure is inadequate to depict the fact that experimental studies have shown two unpaired electrons in each oxygen molecule<em>.<\/em><sub>\r\n<\/sub><\/li>\r\n \t<li>H<sub>2<\/sub>CO:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211507\/CNX_Chem_07_03_Question7b_img1.jpg\" alt=\"A Lewis structure shows a carbon atom that is single bonded to two hydrogen atoms and double bonded to an oxygen atom. The oxygen atom has two lone pairs of electrons.\" \/><\/li>\r\n \t<li>AsF<sub>3<\/sub>:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211508\/CNX_Chem_07_03_Question7c_img1.jpg\" alt=\"A Lewis structure shows an arsenic atom single bonded to three fluorine atoms. Each fluorine atom has a lone pair of electrons.\" \/><\/li>\r\n \t<li>SiCl<sub>4<\/sub>:\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211510\/CNX_Chem_07_03_Question7e_img1.jpg\" alt=\"A Lewis structure shows a silicon atom that is single bonded to four chlorine atoms. Each chlorine atom has three lone pairs of electrons.\" \/><\/li>\r\n<\/ol>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<h2>Glossary<\/h2>\r\n<strong>double bond: <\/strong>covalent bond in which two pairs of electrons are shared between two atoms\r\n\r\n<strong>free radical: <\/strong>molecule that contains an odd number of electrons\r\n\r\n<strong>hypervalent molecule: <\/strong>molecule containing at least one main group element that has more than eight electrons in its valence shell\r\n\r\n<strong>Lewis structure: <\/strong>diagram showing lone pairs and bonding pairs of electrons in a molecule or an ion\r\n\r\n<strong>Lewis symbol: <\/strong>symbol for an element or monatomic ion that uses a dot to represent each valence electron in the element or ion\r\n\r\n<strong>lone pair: <\/strong>two (a pair of) valence electrons that are not used to form a covalent bond\r\n\r\n<strong>octet rule: <\/strong>guideline that states main group atoms will form structures in which eight valence electrons interact with each nucleus, counting bonding electrons as interacting with both atoms connected by the bond\r\n\r\n<strong>single bond: <\/strong>bond in which a single pair of electrons is shared between two atoms\r\n\r\n<strong>triple bond: <\/strong>bond in which three pairs of electrons are shared between two atoms","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Write Lewis symbols for neutral atoms and ions<\/li>\n<li>Draw Lewis structures depicting the bonding in simple molecules<\/li>\n<\/ul>\n<\/div>\n<p>We have discussed the various types of bonds that form between atoms and\/or ions. In all cases, these bonds involve the sharing or transfer of valence shell electrons between atoms. In this section, we will explore the typical method for depicting valence shell electrons and chemical bonds, namely Lewis symbols and Lewis structures.<\/p>\n<h2>Lewis Symbols<\/h2>\n<p>We use Lewis symbols to describe valence electron configurations of atoms and monatomic ions. A <strong>Lewis symbol <\/strong>consists of an elemental symbol surrounded by one dot for each of its valence electrons:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211351\/CNX_Chem_07_03_Lewisstruct1_img1.jpg\" alt=\"A Lewis structure of calcium is shown. A lone pair of electrons are shown to the right of the symbol.\" width=\"325\" height=\"34\" \/><\/p>\n<p>Figure 1 shows the Lewis symbols for the elements of the third period of the periodic table.<\/p>\n<div style=\"width: 891px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211352\/CNX_Chem_07_03_3rowLewis1.jpg\" alt=\"A table is shown that has three columns and nine rows. The header row reads \u201cAtoms,\u201d \u201cElectronic Configuration,\u201d and \u201cLewis Symbol.\u201d The first column contains the words \u201csodium,\u201d \u201cmagnesium,\u201d \u201caluminum,\u201d \u201csilicon,\u201d \u201cphosphorus,\u201d \u201csulfur,\u201d \u201cchlorine,\u201d and \u201cargon.\u201d The second column contains the symbols and numbers \u201c[ N e ] 3 s superscript 2,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 1,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 2,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 3,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 4,\u201d \u201c[ N e ] 3 s superscript 2, 3 p superscript 5,\u201d and \u201c[ N e ] 3 s superscript 2, 3 p superscript 6.\u201d The third column contains Lewis structures for N a with one dot, M g with two dots, A l with three dots, Si with four dots, P with five dots, S with six dots, C l with seven dots, and A r with eight dots.\" width=\"881\" height=\"416\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1. Lewis symbols illustrating the number of valence electrons for each element in the third period of the periodic table.<\/p>\n<\/div>\n<p>Lewis symbols can also be used to illustrate the formation of cations from atoms, as shown here for sodium and calcium:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211353\/CNX_Chem_07_03_NaCa_img1.jpg\" alt=\"Two diagrams are shown. The left diagram shows a Lewis dot structure of sodium with one dot, then a right-facing arrow leading to a sodium symbol with a superscripted plus sign, a plus sign, and the letter \u201ce\u201d with a superscripted negative sign. The terms below this diagram read \u201cSodium atom\u201d and \u201cSodium cation.\u201d The right diagram shows a Lewis dot structure of calcium with two dots, then a right-facing arrow leading to a calcium symbol with a superscripted two and a plus sign, a plus sign, and the value \u201c2e\u201d with a superscripted negative sign. The terms below this diagram read \u201cCalcium atom\u201d and \u201cCalcium cation.\u201d\" width=\"885\" height=\"81\" \/><\/p>\n<p>Likewise, they can be used to show the formation of anions from atoms, as shown below for chlorine and sulfur:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211355\/CNX_Chem_07_03_ClS_img1.jpg\" alt=\"Two diagrams are shown. The left diagram shows a Lewis dot structure of chlorine with seven dots and the letter \u201ce\u201d with a superscripted negative sign, then a right-facing arrow leading to a chlorine symbol with eight dots and a superscripted negative sign. The terms below this diagram read, \u201cChlorine atom,\u201d and, \u201cChlorine anion.\u201d The right diagram shows a Lewis dot structure of sulfur with six dots and the symbol \u201c2e\u201d with a superscripted negative sign, then a right-facing arrow leading to a sulfur symbol with eight dots and a superscripted two and negative sign. The terms below this diagram read, \u201cSulfur atom,\u201d and, \u201cSulfur anion.\u201d\" width=\"883\" height=\"89\" \/><\/p>\n<p>Figure 2 demonstrates the use of Lewis symbols to show the transfer of electrons during the formation of ionic compounds.<\/p>\n<div style=\"width: 894px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211357\/CNX_Chem_07_03_IonLewis1.jpg\" alt=\"A table is shown with four rows. The header row reads \u201cMetal,\u201d \u201cNonmetal,\u201d and \u201cIonic Compound.\u201d The second row shows the Lewis structures of a reaction. A sodium symbol with one dot, a plus sign, and a chlorine symbol with seven dots lie to the left of a right-facing arrow. To the right of the arrow a sodium symbol with a superscripted plus sign is drawn next to a chlorine symbol with eight dots surrounded by brackets with a superscripted negative sign. One of the dots on the C l atom is red. The terms \u201csodium atom,\u201d \u201cchlorine atom,\u201d and \u201csodium chloride ( sodium ion and chloride ion )\u201d are written under the reaction. The third row shows the Lewis structures of a reaction. A magnesium symbol with two red dots, a plus sign, and an oxygen symbol with six dots lie to the left of a right-facing arrow. To the right of the arrow a magnesium symbol with a superscripted two and a plus sign is drawn next to an oxygen symbol with eight dots, two of which are red, surrounded by brackets with a superscripted two a and a negative sign. The terms \u201cmagnesium atom,\u201d \u201coxygen atom,\u201d and \u201cmagnesium oxide ( magnesium ion and oxide ion )\u201d are written under the reaction. The fourth row shows the Lewis structures of a reaction. A calcium symbol with two red dots, a plus sign, and a fluorine symbol with a coefficient of two and seven dots lie to the left of a right-facing arrow. To the right of the arrow a calcium symbol with a superscripted two and a plus sign is drawn next to a fluorine symbol with eight dots, one of which is red, surrounded by brackets with a superscripted negative sign and a subscripted two. The terms \u201ccalcium atom,\u201d \u201cfluorine atoms,\u201d and \u201ccalcium fluoride ( calcium ion and two fluoride ions )\u201d are written under the reaction.\" width=\"884\" height=\"457\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 2. Cations are formed when atoms lose electrons, represented by fewer Lewis dots, whereas anions are formed by atoms gaining electrons. The total number of electrons does not change.<\/p>\n<\/div>\n<h2>Lewis Structures<\/h2>\n<p>We also use Lewis symbols to indicate the formation of covalent bonds, which are shown in<strong> Lewis structures<\/strong>, drawings that describe the bonding in molecules and polyatomic ions. For example, when two chlorine atoms form a chlorine molecule, they share one pair of electrons:<\/p>\n<p><img decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211358\/CNX_Chem_07_03_C12dot_img1.jpg\" alt=\"A Lewis dot diagram shows a reaction. Two chlorine symbols, each surrounded by seven dots are separated by a plus sign. The dots on the first atom are all black and the dots on the second atom are all read. The phrase, \u201cChlorine atoms\u201d is written below. A right-facing arrow points to two chlorine symbols, each with six dots surrounding their outer edges and a shared pair of dots in between. One of the shared dots is black and one is red. The phrase, \u201cChlorine molecule\u201d is written below.\" \/><\/p>\n<p>The Lewis structure indicates that each Cl atom has three pairs of electrons that are not used in bonding (called <strong>lone pairs<\/strong>) and one shared pair of electrons (written between the atoms). A dash (or line) is sometimes used to indicate a shared pair of electrons:<\/p>\n<p><img decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211400\/CNX_Chem_07_03_Cl2dash_img1.jpg\" alt=\"Two Lewis structures are shown. The left-hand structure shows two H atoms connected by a single bond. The right-hand structure shows two C l atoms connected by a single bond and each surrounded by six dots.\" \/><\/p>\n<p>A single shared pair of electrons is called a <strong>single bond<\/strong>. Each Cl atom interacts with eight valence electrons: the six in the lone pairs and the two in the single bond.<\/p>\n<h3>The Octet Rule<\/h3>\n<p>The other halogen molecules (F<sub>2<\/sub>, Br<sub>2<\/sub>, I<sub>2<\/sub>, and At<sub>2<\/sub>) form bonds like those in the chlorine molecule: one single bond between atoms and three lone pairs of electrons per atom. This allows each halogen atom to have a noble gas electron configuration. The tendency of main group atoms to form enough bonds to obtain eight valence electrons is known as the <strong>octet rule<\/strong>.<\/p>\n<p>The number of bonds that an atom can form can often be predicted from the number of electrons needed to reach an octet (eight valence electrons); this is especially true of the nonmetals of the second period of the periodic table (C, N, O, and F). For example, each atom of a group 14 element has four electrons in its outermost shell and therefore requires four more electrons to reach an octet. These four electrons can be gained by forming four covalent bonds, as illustrated here for carbon in CCl<sub>4<\/sub> (carbon tetrachloride) and silicon in SiH<sub>4<\/sub> (silane). Because hydrogen only needs two electrons to fill its valence shell, it is an exception to the octet rule. The transition elements and inner transition elements also do not follow the octet rule:<\/p>\n<p><img decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211401\/CNX_Chem_07_03_XY4struc_img1.jpg\" alt=\"Two sets of Lewis dot structures are shown. The left structures depict five C l symbols in a cross shape with eight dots around each, the word \u201cor\u201d and the same five C l symbols, connected by four single bonds in a cross shape. The name \u201cCarbon tetrachloride\u201d is written below the structure. The right hand structures show a S i symbol, surrounded by eight dots and four H symbols in a cross shape. The word \u201cor\u201d separates this from an S i symbol with four single bonds connecting the four H symbols in a cross shape. The name \u201cSilane\u201d is written below these diagrams.\" \/><\/p>\n<p>Group 15 elements such as nitrogen have five valence electrons in the atomic Lewis symbol: one lone pair and three unpaired electrons. To obtain an octet, these atoms form three covalent bonds, as in NH<sub>3<\/sub> (ammonia). Oxygen and other atoms in group 16 obtain an octet by forming two covalent bonds:<\/p>\n<p><img decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211402\/CNX_Chem_07_03_numbonds_img1.jpg\" alt=\"Three Lewis structures labeled, \u201cAmmonia,\u201d \u201cWater,\u201d and \u201cHydrogen fluoride\u201d are shown. The left structure shows a nitrogen atom with a lone pair of electrons and single bonded to three hydrogen atoms. The middle structure shows an oxygen atom with two lone pairs of electrons and two singly-bonded hydrogen atoms. The right structure shows a hydrogen atom single bonded to a fluorine atom that has three lone pairs of electrons.\" \/><\/p>\n<h3>Double and Triple Bonds<\/h3>\n<p>As previously mentioned, when a pair of atoms shares one pair of electrons, we call this a single bond. However, a pair of atoms may need to share more than one pair of electrons in order to achieve the requisite octet. A <strong>double bond <\/strong>forms when two pairs of electrons are shared between a pair of atoms, as between the carbon and oxygen atoms in CH<sub>2<\/sub>O (formaldehyde) and between the two carbon atoms in C<sub>2<\/sub>H<sub>4<\/sub> (ethylene):<img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-6464 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/915\/2015\/04\/20153809\/CNX_Chem_07_03_DoubleBond_img1_rev1.jpg\" alt=\"Two pairs of Lewis structures are shown. The left pair of structures shows a carbon atom forming single bonds to two hydrogen atoms. There are four electrons between the C atom and an O atom. The O atom also has two pairs of dots. The word \u201cor\u201d separates this structure from the same diagram, except this time there is a double bond between the C atom and O atom. The name, \u201cFormaldehyde\u201d is written below these structures. On the the left are two C atoms with four dots in between them and each forming single bonds to two H atoms. The word \u201cor\u201d lies to the left of the second structure, which is the same except that the C atoms form double bonds with one another. The name, \u201cEthylene\u201d is written below these structures.\" width=\"790\" height=\"182\" \/><\/p>\n<p>A <strong>triple bond<\/strong> forms when three electron pairs are shared by a pair of atoms, as in nitrogen gas (N<sub>2<\/sub>):<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1715\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14032405\/nitrogen-gas.jpg\" alt=\"\" width=\"135\" height=\"41\" \/><\/p>\n<h2>Writing Lewis Structures with the Octet Rule<\/h2>\n<p>For very simple molecules and molecular ions, we can write the Lewis structures by merely pairing up the unpaired electrons on the constituent atoms. See these examples:<\/p>\n<p><img decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211406\/CNX_Chem_07_03_Unprelec_img1.jpg\" alt=\"Three reactions are shown with Lewis dot diagrams. The first shows a hydrogen with one red dot, a plus sign and a bromine with seven dots, one of which is red, connected by a right-facing arrow to a hydrogen and bromine with a pair of red dots in between them. There are also three lone pairs on the bromine. The second reaction shows a hydrogen with a coefficient of two and one red dot, a plus sign, and a sulfur atom with six dots, two of which are red, connected by a right facing arrow to two hydrogen atoms and one sulfur atom. There are two red dots in between the two hydrogen atoms and the sulfur atom. Both pairs of these dots are red. The sulfur atom also has two lone pairs of dots. The third reaction shows two nitrogen atoms each with five dots, three of which are red, separated by a plus sign, and connected by a right-facing arrow to two nitrogen atoms with six red electron dots in between one another. Each nitrogen atom also has one lone pair of electrons.\" \/><\/p>\n<p>For more complicated molecules and molecular ions, it is helpful to follow the step-by-step procedure outlined here:<\/p>\n<ol>\n<li>Determine the total number of valence (outer shell) electrons.<\/li>\n<li>Draw a skeleton structure of the molecule, arranging the atoms around a central atom. (Generally, the atom that can form more bonding pairs will be the central element, or as we will learn later, the least electronegative element will be the central atom.) Connect each atom to the central atom with a single bond (one electron pair).<\/li>\n<li>Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.<\/li>\n<li>Place all remaining electrons on the central atom.<\/li>\n<li>Rearrange the electrons of the outer atoms to make multiple bonds with the central atom in order to obtain octets wherever possible.<\/li>\n<\/ol>\n<p>Let us determine the Lewis structure of PBr<sub>3<\/sub> using the steps above:<\/p>\n<ul>\n<li>Step 1: Determine the total number of valence (outer shell) electrons.<\/li>\n<\/ul>\n<p style=\"text-align: center;\">[latex]\\large \\begin{array}{l}\\\\ \\phantom{\\rule{0.8em}{0ex}}{\\text{PBr}}_{3}\\\\ \\phantom{\\rule{0.8em}{0ex}}\\text{P: 5 valence electrons\/atom}\\times \\text{1 atom}=5\\\\ \\underline{+\\text{Br: 7 valence electron\/atom}\\times \\text{3 atoms}=21}\\\\ \\\\ \\phantom{\\rule{15.95em}{0ex}}=\\text{26 valence electrons}\\end{array}[\/latex]<\/p>\n<ul>\n<li>Step 2: Draw a skeleton structure of the molecule, arranging the atoms around a central atom. (Generally, the least electronegative element should be placed in the center.) Connect each atom to the central atom with a single bond (one electron pair).<\/li>\n<\/ul>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1507 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/19194359\/PBr3.jpg\" alt=\"Lewis diagram of PBr3 is shown. The one phosphorus single boned to three bromine atoms.\" width=\"228\" height=\"128\" \/><\/p>\n<ul>\n<li>Step 3: Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.<\/li>\n<li><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1508\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/19195038\/PBr3Lewis.jpg\" alt=\"Lewis doagram of PBr3. A single atom of phosphorus bonded to three bromine atoms. Each bromine atom has three lone pairs.\" width=\"254\" height=\"162\" \/>Step 4: Place all remaining electrons on the central atom.<\/li>\n<\/ul>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1510\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/19200010\/PBr3Lewisstructure.jpg\" alt=\"Lewis structure for PBr3 is shown. All atoms have octets. Phorsphorus is singly bonded to three bromine's. The phorphorus atom has one lone pair, while each bromine has three lone pairs.\" width=\"250\" height=\"157\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"padding-left: 30px;\">Note: Step 5: Is not needed since all atoms have an octet.<\/p>\n<p>&nbsp;<\/p>\n<p>Let us determine the Lewis structure of CH<sub>2<\/sub>O.<\/p>\n<ul>\n<li>Step 1: Determine the total number of valence (outer shell) electrons.<\/li>\n<\/ul>\n<p style=\"text-align: center;\">[latex]\\large \\begin{array}{l}\\\\ \\phantom{\\rule{0.8em}{0ex}}{\\text{H}_{2}}\\text{CO}\\\\ \\phantom{\\rule{0.8em}{0ex}}\\text{H: 1 valence electron\/atom}\\times \\text{2 atom}=2\\\\\\text{C: 4 valence electrons\/atom}\\times \\text{1 atom}=4\\\\ \\underline{+\\text{O: 6 valence electrons\/atom}\\times \\text{1 atoms}=6}\\\\ \\\\ \\phantom{\\rule{15.95em}{0ex}}=\\text{12 valence electrons}\\end{array}[\/latex]<\/p>\n<ul>\n<li>Step 2: Draw a skeleton structure of the molecule, arranging the atoms around a central atom. (Generally, the least electronegative element should be placed in the center.) Connect each atom to the central atom with a single bond (one electron pair).<\/li>\n<\/ul>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1512\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20021300\/H2COskeletal.jpg\" alt=\"Lewis diagram shown. Central atom is carbon, bonded to one oxygen and two hydrogens.\" width=\"213\" height=\"125\" \/><\/p>\n<ul>\n<li>Step 3: Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.<\/li>\n<\/ul>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1513\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20021728\/H2COlonepairs.jpg\" alt=\"\" width=\"207\" height=\"131\" \/><\/p>\n<ul>\n<li>Step 4: Not needed, since all electrons have been placed.\u00a0 However, carbon does not have an octet,<\/li>\n<li>Step 5: Rearrange the electrons of the outer atoms to make multiple bonds with the central atom in order to obtain octets wherever possible.<\/li>\n<\/ul>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1514\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20022000\/H2COfinal.jpg\" alt=\"\" width=\"203\" height=\"119\" \/><\/p>\n<div class=\"textbox examples\">\n<h3>Example 1: Writing Lewis Structures<\/h3>\n<p>NASA\u2019s Cassini-Huygens mission detected a large cloud of toxic hydrogen cyanide (HCN) on Titan, one of Saturn\u2019s moons. What are the Lewis structures of these molecules?<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q131813\">Show Step 1<\/span><\/p>\n<div id=\"q131813\" class=\"hidden-answer\" style=\"display: none\">\n<p><em><strong>Step 1:<\/strong> Calculate the number of valence electrons.<\/em><br \/>\nHCN: (1 \u00d7 1) + (4 \u00d7 1) + (5 \u00d7 1) = 10<\/p>\n<\/div>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q131814\">Show Step 2<\/span><\/p>\n<div id=\"q131814\" class=\"hidden-answer\" style=\"display: none\">\n<p><em><strong>Step 2.<\/strong> Draw a skeleton and connect the atoms with single bonds.<\/em> Remember that H is never a central atom:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1717\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14032949\/HCN.jpg\" alt=\"\" width=\"167\" height=\"107\" \/><\/p>\n<\/div>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q131815\">Show Step 3<\/span><\/p>\n<div id=\"q131815\" class=\"hidden-answer\" style=\"display: none\">\n<p><em><strong>Step 3<\/strong>: Where needed, distribute electrons to the terminal atoms:<\/em><\/p>\n<p>HCN: six electrons placed on N<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1716\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14032831\/HCN1.jpg\" alt=\"\" width=\"177\" height=\"111\" \/><\/p>\n<\/div>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q131816\">Show Step 4<\/span><\/p>\n<div id=\"q131816\" class=\"hidden-answer\" style=\"display: none\">\n<p><em><strong>Step 4<\/strong>: Where needed, place remaining electrons on the central atom:<\/em><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1718\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14033129\/HCN2.jpg\" alt=\"\" width=\"181\" height=\"98\" \/>HCN: no electrons remain<\/p>\n<\/div>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q131817\">Show Step 5<\/span><\/p>\n<div id=\"q131817\" class=\"hidden-answer\" style=\"display: none\">\n<p><em><strong>Step 5<\/strong>: Where needed, rearrange electrons to form multiple bonds in order to obtain an octet on each atom:<\/em><br \/>\nHCN: form two more C\u2013N bonds<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1719\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/14033229\/HCN3.jpg\" alt=\"\" width=\"174\" height=\"131\" \/><\/p>\n<\/div>\n<\/div>\n<p><strong>Check Your Learning<\/strong><\/p>\n<p>Carbon dioxide, CO<sub>2<\/sub>, is a product of the combustion of fossil fuels. CO<sub>2<\/sub> has been implicated in global climate change. What is the Lewis structure of CO<sub>2<\/sub>?<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q13181\">Show Answer<\/span><\/p>\n<div id=\"q13181\" class=\"hidden-answer\" style=\"display: none\">\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1515\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2835\/2018\/08\/20022859\/CO2.jpg\" alt=\"\" width=\"183\" height=\"53\" \/><\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Concepts and Summary<\/h3>\n<p>Valence electronic structures can be visualized by drawing Lewis symbols (for atoms and monatomic ions) and Lewis structures (for molecules and polyatomic ions). Lone pairs, unpaired electrons, and single, double, or triple bonds are used to indicate where the valence electrons are located around each atom in a Lewis structure. Most structures\u2014especially those containing second row elements\u2014obey the octet rule, in which every atom (except H) is surrounded by eight electrons. Exceptions to the octet rule occur for odd-electron molecules (free radicals), electron-deficient molecules, and hypervalent molecules.<\/p>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<ol>\n<li>Write the Lewis symbols for each of the following ions:\n<ol style=\"list-style-type: lower-alpha;\">\n<li>As<sup>3\u2013 <\/sup><\/li>\n<li>I<sup>\u2013 <\/sup><\/li>\n<li>Be<sup>2+ <\/sup><\/li>\n<li>O<sup>2\u2013 <\/sup><\/li>\n<li>Ga<sup>3+ <\/sup><\/li>\n<li>Li<sup>+ <\/sup><\/li>\n<li>N<sup>3\u2013<\/sup><\/li>\n<\/ol>\n<\/li>\n<li>Many monatomic ions are found in seawater, including the ions formed from the following list of elements. Write the Lewis symbols for the monatomic ions formed from the following elements:\n<ol style=\"list-style-type: lower-alpha;\">\n<li>Cl<\/li>\n<li>Na<\/li>\n<li>Mg<\/li>\n<li>Ca<\/li>\n<li>K<\/li>\n<li>Br<\/li>\n<li>Sr<\/li>\n<li>F<\/li>\n<\/ol>\n<\/li>\n<li>Write the Lewis symbols of the ions in each of the following ionic compounds and the Lewis symbols of the atom from which they are formed:\n<ol style=\"list-style-type: lower-alpha;\">\n<li>MgS<\/li>\n<li>Al<sub>2<\/sub>O<sub>3 <\/sub><\/li>\n<li>GaCl<sub>3 <\/sub><\/li>\n<li>K<sub>2<\/sub>O<\/li>\n<li>Li<sub>3<\/sub>N<\/li>\n<li>KF<\/li>\n<\/ol>\n<\/li>\n<li>In the Lewis structures listed below, M and X represent various elements in the third period of the periodic table. Write the formula of each compound using the chemical symbols of each element:\n<ol style=\"list-style-type: lower-alpha;\">\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211453\/CNX_Chem_07_03_MXLewisa_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted two positive sign. The right shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign outside of the brackets.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211454\/CNX_Chem_07_03_MXLewisb_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted three positive sign. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted negative sign and a subscripted three both outside of the brackets.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211455\/CNX_Chem_07_03_MXLewisc_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted positive sign and a subscripted two outside of the brackets. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign outside of the brackets.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211456\/CNX_Chem_07_03_MXLewisd_img1.jpg\" alt=\"Two Lewis structures are shown side-by-side, each surrounded by brackets. The left structure shows the symbol M with a superscripted three positive sign and a subscripted two outside of the brackets. The right structure shows the symbol X surrounded by four lone pairs of electrons with a superscripted two negative sign and subscripted three both outside of the brackets.\" \/><\/li>\n<\/ol>\n<\/li>\n<li>Write the Lewis structure for the diatomic molecule P<sub>2<\/sub>, an unstable form of phosphorus found in high-temperature phosphorus vapor.<\/li>\n<li>Write Lewis structures for the following:\n<ol style=\"list-style-type: lower-alpha;\">\n<li>H<sub>2 <\/sub><\/li>\n<li>HBr<\/li>\n<li>PCl<sub>3 <\/sub><\/li>\n<\/ol>\n<\/li>\n<li>Write Lewis structures for the following:\n<ol style=\"list-style-type: lower-alpha;\">\n<li>O<sub>2 <\/sub><\/li>\n<li>H<sub>2<\/sub>CO<\/li>\n<li>AsF<sub>3 <\/sub><\/li>\n<li>SiCl<sub>4 <\/sub><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q152254\">Selected Answers<\/span><\/p>\n<div id=\"q152254\" class=\"hidden-answer\" style=\"display: none\">\n1. The Lewis symbol for each ion is as follows:<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>eight electrons:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211436\/CNX_Chem_07_03_Question1a_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for arsenic, A s, surrounded by eight dots and a superscripted three negative sign.\" \/><\/li>\n<li>eight electrons:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211437\/CNX_Chem_07_03_Question1b_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for iodine, I, surrounded by eight dots and a superscripted negative sign.\" \/><\/li>\n<li>no electrons Be<sup>2+<\/sup><\/li>\n<li>eight electrons:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211438\/CNX_Chem_07_03_Question1d_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for oxygen, O, surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\n<li>no electrons Ga<sup>3+<\/sup><\/li>\n<li>no electrons Li<sup>+<\/sup><\/li>\n<li>eight electrons:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211439\/CNX_Chem_07_03_Question1g_img1.jpg\" alt=\"A Lewis dot diagram shows the symbol for nitrogen, N, surrounded by eight dots and a superscripted three negative sign.\" \/><\/li>\n<\/ol>\n<p>3. The Lewis symbols are as follows:<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211445\/CNX_Chem_07_03_Exercise3a_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol M g with a superscripted two positive sign while the right shows the symbol S surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211446\/CNX_Chem_07_03_Exercise3b_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol A l with a superscripted three positive sign while the right shows the symbol O surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211447\/CNX_Chem_07_03_Exercise3c_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol G a with a superscripted three positive sign while the right shows the symbol C l surrounded by eight dots and a superscripted negative sign.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211448\/CNX_Chem_07_03_Exercise3d_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol K with a superscripted positive sign while the right shows the symbol O surrounded by eight dots and a superscripted two negative sign.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211449\/CNX_Chem_07_03_Exercise3e_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol L i with a superscripted positive sign while the right shows the symbol N surrounded by eight dots and a superscripted three negative sign.\" \/><\/li>\n<li><img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211452\/CNX_Chem_07_03_Exercise3f_img1.jpg\" alt=\"Two Lewis structures are shown. The left shows the symbol K with a superscripted positive sign while the right shows the symbol F surrounded by eight dots and a superscripted negative sign.\" \/><\/li>\n<\/ol>\n<p>5. <img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211457\/CNX_Chem_07_03_Question5_img1.jpg\" alt=\"A Lewis diagram shows two phosphorus atoms triple bonded together each with one lone electron pair.\" \/><\/p>\n<p>7. The Lewis structures are as follows:<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>O<sub>2<\/sub>:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211507\/CNX_Chem_07_03_Question7a_img1.jpg\" alt=\"A Lewis structure shows two oxygen atoms double bonded together, and each has two lone pairs of electrons.\" \/><br \/>\nIn this case, the Lewis structure is inadequate to depict the fact that experimental studies have shown two unpaired electrons in each oxygen molecule<em>.<\/em><sub><br \/>\n<\/sub><\/li>\n<li>H<sub>2<\/sub>CO:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211507\/CNX_Chem_07_03_Question7b_img1.jpg\" alt=\"A Lewis structure shows a carbon atom that is single bonded to two hydrogen atoms and double bonded to an oxygen atom. The oxygen atom has two lone pairs of electrons.\" \/><\/li>\n<li>AsF<sub>3<\/sub>:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211508\/CNX_Chem_07_03_Question7c_img1.jpg\" alt=\"A Lewis structure shows an arsenic atom single bonded to three fluorine atoms. Each fluorine atom has a lone pair of electrons.\" \/><\/li>\n<li>SiCl<sub>4<\/sub>:<br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/887\/2015\/04\/23211510\/CNX_Chem_07_03_Question7e_img1.jpg\" alt=\"A Lewis structure shows a silicon atom that is single bonded to four chlorine atoms. Each chlorine atom has three lone pairs of electrons.\" \/><\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<h2>Glossary<\/h2>\n<p><strong>double bond: <\/strong>covalent bond in which two pairs of electrons are shared between two atoms<\/p>\n<p><strong>free radical: <\/strong>molecule that contains an odd number of electrons<\/p>\n<p><strong>hypervalent molecule: <\/strong>molecule containing at least one main group element that has more than eight electrons in its valence shell<\/p>\n<p><strong>Lewis structure: <\/strong>diagram showing lone pairs and bonding pairs of electrons in a molecule or an ion<\/p>\n<p><strong>Lewis symbol: <\/strong>symbol for an element or monatomic ion that uses a dot to represent each valence electron in the element or ion<\/p>\n<p><strong>lone pair: <\/strong>two (a pair of) valence electrons that are not used to form a covalent bond<\/p>\n<p><strong>octet rule: <\/strong>guideline that states main group atoms will form structures in which eight valence electrons interact with each nucleus, counting bonding electrons as interacting with both atoms connected by the bond<\/p>\n<p><strong>single bond: <\/strong>bond in which a single pair of electrons is shared between two atoms<\/p>\n<p><strong>triple bond: <\/strong>bond in which three pairs of electrons are shared between two atoms<\/p>\n","protected":false},"author":6181,"menu_order":3,"template":"","meta":{"_candela_citation":"[]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1347","chapter","type-chapter","status-publish","hentry"],"part":352,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/1347","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/wp\/v2\/users\/6181"}],"version-history":[{"count":19,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/1347\/revisions"}],"predecessor-version":[{"id":1909,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/1347\/revisions\/1909"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/pressbooks\/v2\/parts\/352"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/pressbooks\/v2\/chapters\/1347\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/wp\/v2\/media?parent=1347"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/pressbooks\/v2\/chapter-type?post=1347"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/wp\/v2\/contributor?post=1347"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-introductorychemistry\/wp-json\/wp\/v2\/license?post=1347"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}