What Is Covalent Bonding?

Covalent bonding is a type of chemical bonding that occurs when two atoms share one or more pairs of electrons.

This type of bonding usually happens between non-metal atoms. By sharing electrons, the atoms achieve a stable outer electron shell, similar to the structure of noble gases.

Covalent bonds form molecules, which are groups of atoms held together by shared electrons.

Why Atoms Form Covalent Bonds

Atoms form covalent bonds to achieve a stable electron configuration.

Most atoms try to reach:

• 8 electrons in the outer shell (octet rule)
• 2 electrons for hydrogen

Sharing electrons allows atoms to complete their outer shells without gaining or losing electrons.

Example – Hydrogen Molecule (H₂)

Hydrogen atoms each have one electron in their outer shell.

When two hydrogen atoms bond:

• Each atom shares its electron
• A shared pair of electrons forms a covalent bond

This produces a hydrogen molecule (H₂).

Diagram representation:

H : H

Both atoms now have a stable outer shell of 2 electrons.

Example – Water Molecule (H₂O)

Water is formed when oxygen shares electrons with hydrogen atoms.

Oxygen has 6 electrons in its outer shell and needs 2 more electrons to become stable.

In a water molecule:

• Oxygen shares one electron with each hydrogen atom
• Two covalent bonds are formed

This creates the H₂O molecule.

Example – Carbon Dioxide (CO₂)

Carbon dioxide forms when carbon shares electrons with two oxygen atoms.

Carbon has 4 electrons in its outer shell and needs 4 more electrons to complete the octet.

In CO₂:

• Carbon forms two double covalent bonds with oxygen atoms

Structure:

O = C = O

This molecule contains double covalent bonds.

Types of Covalent Bonds

Covalent bonds can involve different numbers of shared electron pairs.

Single Covalent Bond

One pair of electrons is shared.

Example:

H₂

Double Covalent Bond

Two pairs of electrons are shared.

Example:

O₂

Triple Covalent Bond

Three pairs of electrons are shared.

Example:

N₂

Properties of Simple Covalent Molecules

Covalent compounds often have the following properties:

• Low melting and boiling points
• Usually do not conduct electricity
• Often exist as gases or liquids

This is because the forces between molecules are relatively weak.

Example:

Carbon dioxide and water are both covalent molecules.

Importance of Covalent Bonding

Covalent bonding is essential for many substances found in everyday life.

Examples include:

• Water (H₂O)
• Carbon dioxide (CO₂)
• Methane (CH₄)
• Organic molecules in living organisms

Many biological molecules such as proteins, DNA, and carbohydrates involve covalent bonding.

Exam Tip (5070)

Students are often asked to:

• Define covalent bonding
• Draw dot-and-cross diagrams
• Explain properties of covalent compounds

Example exam question:

Why do covalent compounds usually have low melting points?

Answer:

Because the forces between molecules are weak, so little energy is needed to separate them.

Practice Question

How many covalent bonds are present in a water molecule?

Answer

A water molecule contains two covalent bonds between oxygen and hydrogen atoms.

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