1.4.3 Covalent Bonding

Covalent bonding involves the sharing of electrons between atoms to achieve a full outer electron shell, giving the atoms greater stability. Covalent bonds typically form between non-metal atoms.

What is Covalent Bonding?

• Single covalent bond: A single shared pair of electrons between two atoms. For example, in a hydrogen molecule (H₂), each hydrogen atom shares one electron, forming a single covalent bond.
• Multiple covalent bonds: When more than one pair of electrons is shared between atoms. For example:
  • Double bond: Two pairs of electrons are shared (e.g., O₂, where two oxygen atoms share two pairs of electrons).
  • Triple bond: Three pairs of electrons are shared (e.g., N₂, where two nitrogen atoms share three pairs of electrons).

Representing Covalent Bonds

Covalent bonds can be represented using lines to show the shared pairs of electrons:

• A single line (−) represents a single covalent bond.

• A double line (＝) represents a double bond.

• A triple line (≡****) represents a triple bond. For example:

• Hydrogen (H₂): $H−H$ This represents a single covalent bond between two hydrogen atoms.

• Oxygen (O₂): $O＝O$ This shows a double bond between two oxygen atoms.

Properties of Covalent Compounds

1. Low melting and boiling points: Covalent molecules generally have lower melting and boiling points compared to ionic compounds because they have weak intermolecular forces (e.g., van der Waals forces or hydrogen bonds).
2. Non-conductive: Most covalent compounds do not conduct electricity, as they do not have free-moving charged particles (ions or electrons).
3. Solubility: Covalent compounds may or may not dissolve in water, depending on their polarity. Polar covalent molecules (e.g., water) tend to dissolve in polar solvents, while non-polar molecules (e.g., methane) dissolve in non-polar solvents like oil.

Key Examples of Covalent Bonding

Water (H₂O)

• Water molecules have a bent structure due to two single covalent bonds between hydrogen and oxygen.
• $H−O−H$

Carbon Dioxide (CO₂)

• Carbon dioxide consists of two double covalent bonds between carbon and oxygen.
• $O＝C＝O$

Methane (CH₄)

• Methane has four single covalent bonds between carbon and hydrogen.
• $H−C−H$