{"id":474,"date":"2018-03-20T14:34:15","date_gmt":"2018-03-20T14:34:15","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-orgbiochemistry\/?post_type=chapter&p=474"},"modified":"2018-08-08T18:31:04","modified_gmt":"2018-08-08T18:31:04","slug":"4-2-covalent-compounds-formulas-and-names","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-monroecc-orgbiochemistry\/chapter\/4-2-covalent-compounds-formulas-and-names\/","title":{"raw":"4.2 Covalent Compounds: Formulas and Names","rendered":"4.2 Covalent Compounds: Formulas and Names"},"content":{"raw":"
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Learning Objectives<\/h3>\r\n
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  1. Determine the chemical formula of a simple covalent compound from its name.<\/li>\r\n \t
  2. Determine the name of a simple covalent compound from its chemical formula.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

    What elements make covalent bonds? Covalent bonds form when two or more nonmetals combine. For example, both hydrogen and oxygen are nonmetals, and when they combine to make water, they do so by forming covalent bonds. Nonmetal atoms in polyatomic ions are joined by covalent bonds, but the ion as a whole participates in ionic bonding. For example, ammonium chloride has ionic bonds between a polyatomic ion, NH4<\/sub>+<\/sup>, and Cl\u2212<\/sup> ions, but within the ammonium ion, the nitrogen and hydrogen atoms are connected by covalent bonds as shown below.\u00a0 Note that the dashed line indicates that the bond extends backward from the page and the wedge indicates that the bond extends forward from the page.\u00a0 Square brackets are used with a charge on the outside of the brackets to indicate a polyatomic ion with the charge belonging to the polyatomic ion as a whole.<\/p>\r\n\"\"\r\n

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    Example 2<\/h3>\r\n

    Is each compound formed from ionic bonds, covalent bonds, or both?<\/p>\r\n\r\n

      \r\n \t
    1. Na2<\/sub>O<\/li>\r\n \t
    2. Na3<\/sub>PO4<\/sub><\/li>\r\n \t
    3. N2<\/sub>O4<\/sub><\/li>\r\n<\/ol>\r\n

      Solution<\/p>\r\n[reveal-answer q=\"569322\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"569322\"]\r\n

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      1. The elements in Na2<\/sub>O are a metal and a nonmetal, which form ionic bonds.<\/li>\r\n \t
      2. Because sodium is a metal and we recognize the formula for the phosphate ion (see Table 3.1 \"Some Polyatomic Ions\"), we know that this compound is ionic. However, polyatomic ions are held together by covalent bonds, so this compound contains both ionic and covalent bonds.<\/li>\r\n \t
      3. The elements in N2<\/sub>O4<\/sub> are both nonmetals, rather than a metal and a nonmetal. Therefore, the atoms form covalent bonds.[\/hidden-answer]<\/li>\r\n<\/ol>\r\n<\/div>\r\n
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        Skill-Building Exercise<\/h3>\r\nIs each compound formed from ionic bonds, covalent bonds, or both?\r\n
          \r\n \t
        1. \r\n
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          Ba(OH)2<\/sub><\/p>\r\n\r\n<\/div><\/li>\r\n \t

        2. \r\n
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          F2<\/sub><\/p>\r\n\r\n<\/div><\/li>\r\n \t

        3. \r\n
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          PCl3<\/sub><\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\nThe chemical formulas for covalent compounds are referred to as molecular formulas<\/span><\/span><\/strong>\u00a0because these compounds exist as separate, discrete molecules. Typically, a molecular formula begins with the nonmetal that is closest to the lower left corner. Then the other nonmetal symbols are listed. Numerical subscripts are used if there is more than one of a particular atom. For example, we have already seen CH4<\/sub>, the molecular formula for methane.\r\n

          B<\/em>inary<\/em> (two-element) covalent compounds are named by different rules than those for simple ionic compounds. The first element in the formula is simply listed using the name of the element. The second element is named by taking the stem of the element name and adding the suffix -ide<\/em>. A system of numerical prefixes is used to specify the number of atoms in a molecule. Table 4.1 \"Numerical Prefixes for Naming Binary Covalent Compounds\"<\/a> lists these numerical prefixes. Normally, no prefix is added to the first element\u2019s name if there is only one atom of the first element in a molecule. If the second element is oxygen, the trailing vowel is usually omitted from the end of a polysyllabic prefix but not a monosyllabic one (that is, we would say \u201cmonoxide\u201d rather than \u201cmonooxide\u201d and \u201ctrioxide\u201d rather than \u201ctroxide\u201d).<\/p>\r\n\r\n

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          Table 4.1<\/span> Numerical Prefixes for Naming Binary Covalent Compounds<\/strong><\/h5>\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
          Number of Atoms in Compound<\/th>\r\nPrefix on the Name of the Element<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
          1<\/td>\r\nmono-*<\/td>\r\n<\/tr>\r\n
          2<\/td>\r\ndi-<\/td>\r\n<\/tr>\r\n
          3<\/td>\r\ntri-<\/td>\r\n<\/tr>\r\n
          4<\/td>\r\ntetra-<\/td>\r\n<\/tr>\r\n
          5<\/td>\r\npenta-<\/td>\r\n<\/tr>\r\n
          6<\/td>\r\nhexa-<\/td>\r\n<\/tr>\r\n
          7<\/td>\r\nhepta-<\/td>\r\n<\/tr>\r\n
          8<\/td>\r\nocta-<\/td>\r\n<\/tr>\r\n
          9<\/td>\r\nnona-<\/td>\r\n<\/tr>\r\n
          10<\/td>\r\ndeca-<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n
          *This prefix is not used for the first element\u2019s name.<\/th>\r\n<\/tr>\r\n<\/tfoot>\r\n<\/table>\r\n<\/div>\r\n

          Let us practice by naming the compound whose molecular formula is CCl4<\/sub>. The name begins with the name of the first element\u2014carbon. The second element, chlorine<\/em>, becomes chloride<\/em>, and we attach the correct numerical prefix (\u201ctetra-\u201d) to indicate that the molecule contains four chlorine atoms. Putting these pieces together gives the name carbon tetrachloride<\/em> for this compound.<\/p>\r\n\r\n

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          Example 3<\/h3>\r\n

          Write the molecular formula for each compound.<\/p>\r\n\r\n

            \r\n \t
          1. chlorine trifluoride<\/li>\r\n \t
          2. phosphorus pentachloride<\/li>\r\n \t
          3. sulfur dioxide<\/li>\r\n \t
          4. dinitrogen pentoxide<\/li>\r\n<\/ol>\r\n

            Solution<\/p>\r\n[reveal-answer q=\"38195\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"38195\"]\r\n\r\nIf there is no numerical prefix on the first element\u2019s name, we can assume that there is only one atom of that element in a molecule.\r\n

              \r\n \t
            1. ClF3<\/sub><\/li>\r\n \t
            2. PCl5<\/sub><\/li>\r\n \t
            3. SO2<\/sub><\/li>\r\n \t
            4. N2<\/sub>O5<\/sub> (The di- prefix on nitrogen indicates that two nitrogen atoms are present.)[\/hidden-answer]<\/li>\r\n<\/ol>\r\n<\/div>\r\n
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              Skill-Building Exercise<\/h3>\r\n

              Write the molecular formula for each compound.<\/p>\r\n\r\n

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              1. \r\n
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                nitrogen dioxide<\/p>\r\n\r\n<\/div><\/li>\r\n \t

              2. \r\n
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                dioxygen difluoride<\/p>\r\n\r\n<\/div><\/li>\r\n \t

              3. \r\n
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                sulfur hexafluoride<\/p>\r\n\r\n<\/div><\/li>\r\n \t

              4. \r\n
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                selenium monoxide<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

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                Note<\/h3>\r\n

                Because it is so unreactive, sulfur hexafluoride is used as a spark suppressant in electrical devices such as transformers.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n

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                Example 4<\/h3>\r\n

                Write the name for each compound.<\/p>\r\n\r\n

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                1. BrF5<\/sub><\/li>\r\n \t
                2. S2<\/sub>F2<\/sub><\/li>\r\n \t
                3. CO<\/li>\r\n<\/ol>\r\n

                  Solution<\/p>\r\n[reveal-answer q=\"481698\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"481698\"]\r\n

                    \r\n \t
                  1. bromine pentafluoride<\/li>\r\n \t
                  2. disulfur difluoride<\/li>\r\n \t
                  3. carbon monoxide[\/hidden-answer]<\/li>\r\n<\/ol>\r\n<\/div>\r\n
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                    Skill-Building Exercise<\/h3>\r\nWrite the name for each compound.\r\n
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                    1. \r\n
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                      CF4<\/sub><\/p>\r\n\r\n<\/div><\/li>\r\n \t

                    2. \r\n
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                      SeCl2<\/sub><\/p>\r\n\r\n<\/div><\/li>\r\n \t

                    3. \r\n
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                      SO3<\/sub><\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

                      For some simple covalent compounds, we use common names rather than systematic names. We have already encountered these compounds, but we list them here explicitly:<\/p>\r\n\r\n