Chemistry IGCSE Topic 4.2: Covalent Bonding and Simple Molecules

Covalent Bond

a bond formed when two non-metal atoms share one or more pairs of electrons.

Why do atoms form covalent bonds?

to form full outer electron shell (noble gas configuration)

Which types of elements form covalent bonds?

Non-metals only.

Single Covalent Bond

One shared pair of electrons

Example: H–H, Cl–Cl

Double Covalent Bond

Two shared pairs of electrons
Example: O=O, CO₂

Triple Covalent Bond

Three shared pairs of electrons
Example: N≡N

Covalent Bond Strength

Single < Double < Triple (triple bonds are strongest)

What do dot-and-cross diagrams show?

How electrons are shared during covalent bonding.

What must dot-and-cross diagrams include for full marks?

• Correct number of outer electrons

• Shared pairs clearly shown

• Full outer shells (except hydrogen)

Why does hydrogen only need 2 electrons?

It can form the smallest shell which is composed of only 2 electrons

How many covalent bonds are in H₂?

One single covalent bond.

Why do simple covalent molecules have low melting and boiling points?

Because the intermolecular forces between molecules are weak

Do covalent molecules conduct electricity?

No, Because they don’t have any delocalised electrons or ions

Are covalent substances usually solids, liquids, or gases at room temperature?

Often gases or liquids (some low-melting solids).

Why are intermolecular forces weak?

Molecules are neutral and only weakly attracted to each other.

What is a simple molecular structure?

Small molecules with strong covalent bonds but weak forces between molecules.