5.3 - Covalent Bond

Formation of a Covalent Bond

• A covalent bond forms when non-metal atoms share electrons so that each atom attains a stable duplet or octet electron arrangement.
• A Lewis structure shows only the valence electrons involved. A line between two atoms represents one shared pair of electrons.

Type and shared electrons	Formation example
Single bond: one pair.	Two chlorine atoms each contribute one electron to form $\mathrm{C}{\mathrm{l}}_2$, represented as $\mathrm{Cl}-\mathrm{Cl}$.
Double bond: two pairs.	Two oxygen atoms each contribute two electrons to form ${\mathrm{O}}_2$, represented as $\mathrm{O}=\mathrm{O}$.
Triple bond: three pairs.	Two nitrogen atoms each contribute three electrons to form ${\mathrm{N}}_2$, represented as $\mathrm{N}\equiv \mathrm{N}$.

• In $\mathrm{C}{\mathrm{l}}_2$, each chlorine atom attains arrangement 2.8.8; in ${\mathrm{O}}_2$ and ${\mathrm{N}}_2$, each atom attains 2.8.

• Diamond is a giant covalent substance: every carbon atom forms four covalent bonds with four other carbon atoms.

• Other examples of covalent bonding include ${\mathrm{H}}_2$, $\mathrm{HCl}$, $\mathrm{C}{\mathrm{O}}_2$ and ${\mathrm{H}}_2\mathrm{O}$.

Comparison of Ionic and Covalent Bonds

Ionic bond	Covalent bond
Forms between metal and non-metal atoms.	Forms between non-metal atoms.
Involves transfer of electrons.	Involves sharing of electrons.
Produces positively and negatively charged ions.	Produces molecules.

Both types involve only valence electrons and allow atoms to attain stable duplet or octet electron arrangements.