Types of Bonds

 

Learning Objective

  • Describe the types of bonds formed between atoms.

Key Points

    • Nonmetals can form different types of bonds depending on their partner atoms. Ionic bonds form when a nonmetal and a metal exchange electrons, while covalent bonds form when electrons are shared between two nonmetals.
    • An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal.
    • A covalent bond involves a pair of electrons being shared between atoms.
    • Atoms form covalent bonds in order to reach a more stable state.
    • A given nonmetal atom can form a single, double, or triple bond with another nonmetal. Which type of bond is formed between the atoms depends on their numbers of valence electrons.

Terms

  • ionic bondA type of chemical bond where two atoms or molecules are connected to each other by electrostatic attraction.
  • covalent bondA type of chemical bond where two atoms are connected to each other by the sharing of two or more electrons.

Nonmetals can form different types of bonds depending on their partner atoms. Ionic bonds form when a nonmetal and a metal exchange electrons, while covalent bonds form when electrons are shared between two nonmetals.

Ionic Bonds

An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some degree of covalent bonding. Thus, an ionic bond is considered a bond where the ionic character is greater than the covalent character. The larger the difference in electronegativity between the two atoms involved in the bond, the more ionic (polar) the bond is. Bonds with partially ionic and partially covalent character are called polar covalent bonds.

Formation of Sodium FlourideThe attraction of oppositely charged atoms and the transfer of electrons leads to the formation of an ionic compound. In this case, NaF.

Covalent Bonds

A covalent bond involves electrons being shared between atoms. The most stable state for an atom occurs when its valence electron shell is full, so atoms form covalent bonds, sharing their valence electrons, so that they achieve a more stable state by filling their valence electron shell.

Polar covalent bonds

Some covalently bounded compounds have a small difference in charge along one direction of the molecule. This difference in charge is called a dipole, and when the covalent bond results in this difference in charge, the bond is called a polar covalent bond.

These kinds of bonds occur when the shared electrons are not shared equally between atoms. If one atom has a higher electronegativity, the electrons will be drawn closer to the nucleus of that atom, resulting in a small net charge around each nucleus of the atoms in the molecule.

If the atoms in the molecule have the same electronegativity (for example, if the atoms are the same, as in N2), then the shared electrons will not be drawn towards one nucleus more than another, and the bond will be nonpolar. Similarly, the higher the difference in electronegativity, the more unequal the sharing of electrons is between the nuclei, and the higher the polarity of the bond.

Number of Bonds Between Covalently Bonded Atoms

A given nonmetal atom can form a single, double, or triple bond with another nonmetal. Which type of bond is formed between the atoms depends on their numbers of valence electrons.

Comparison of Covalent and Ionic Compounds

Compounds that are built from covalent bonds have, in general, some differences in physical properties (ex.  solubility in water, conductivity, boiling point, and melting point) when compared to ionic compounds.

The boiling and melting point of covalent compounds is, in general, higher than for ionic compounds. They are also less soluble and conductive. A rule of thumb is that covalent compounds are more difficult to change than ionic compounds.