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 occurs between non-metal atoms.

Atoms share electrons in order to achieve a stable electronic configuration, usually a full outer electron shell similar to noble gases.

The shared electrons create a strong force that holds the atoms together, forming a covalent bond.

Why Atoms Share Electrons

Atoms tend to become more stable when their outer electron shell is full.

Instead of gaining or losing electrons completely (as in ionic bonding), non-metal atoms often share electrons.

This allows both atoms to reach a stable electron arrangement.

Examples of Covalent Molecules

Several common molecules are formed through covalent bonding.

Hydrogen (H₂)

Hydrogen has 1 electron in its outer shell.

Two hydrogen atoms share their electrons.

This forms a single covalent bond.

Result: H₂ molecule

Oxygen (O₂)

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

Two oxygen atoms share two pairs of electrons.

This forms a double covalent bond.

Result: O₂ molecule

Nitrogen (N₂)

Nitrogen has 5 electrons in its outer shell.

Two nitrogen atoms share three pairs of electrons.

This forms a triple covalent bond.

Result: N₂ molecule

Water (H₂O)

Water is a molecule formed by covalent bonding between hydrogen and oxygen.

Oxygen shares electrons with two hydrogen atoms, forming two single covalent bonds.

Result: H₂O molecule

Dot-and-Cross Diagrams

Chemists often use dot-and-cross diagrams to represent covalent bonds.

In these diagrams:

• Dots represent electrons from one atom
• Crosses represent electrons from another atom

The overlapping electrons show the shared pair of electrons forming the covalent bond.

These diagrams help students visualize how atoms share electrons.

Properties of Simple Covalent Molecules

Substances made of simple covalent molecules have specific properties.

Low Melting and Boiling Points

Simple molecular substances usually have low melting and boiling points.

This is because the forces between molecules are weak intermolecular forces.

Examples include:

• Water
• Carbon dioxide
• Methane

Poor Electrical Conductivity

Simple covalent molecules do not conduct electricity.

This is because they do not contain free-moving charged particles such as ions or electrons.

Usually Gases or Liquids

Many covalent substances exist as gases or liquids at room temperature.

Examples include:

• Oxygen (O₂)
• Carbon dioxide (CO₂)
• Methane (CH₄)

Difference Between Ionic and Covalent Bonding

FeatureIonic BondingCovalent BondingType of atomsMetal + Non-metalNon-metal + Non-metalElectron behaviourElectrons transferredElectrons sharedStructureIonic latticeMoleculesConductivityConducts when molten or dissolvedDoes not conduct

Understanding these differences is essential for chemistry exams.

Why Covalent Bonding Is Important

Covalent bonding explains the formation of many important molecules such as:

• Water
• Oxygen
• Carbon dioxide
• Organic compounds

These substances are essential for life and many chemical processes.

Understanding covalent bonding also helps students learn about molecular structure and chemical reactions.

Exam Tip (5070)

Students are often asked to:

• Define covalent bonding
• Draw dot-and-cross diagrams
• Explain the properties of simple covalent molecules

Example exam question:

Define covalent bonding.

Answer:

A covalent bond is formed when two atoms share a pair of electrons.

Practice Question

Explain how the oxygen molecule (O₂) forms a covalent bond.

Answer

Each oxygen atom has 6 outer shell electrons and needs 2 more electrons to achieve a full shell.

The two oxygen atoms share two pairs of electrons, forming a double covalent bond.

This creates the O₂ molecule.

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