Bonding & Structure

Ionic, covalent & metallic bonding — A-Level Chemistry

Ionic Bonding

Formed by the transfer of electrons from a metal to a non-metal. The metal loses electrons to form a positive cation; the non-metal gains electrons to form a negative anion. The resulting electrostatic attraction between oppositely charged ions is the ionic bond.

Melting Point

High (typically 500-3000°C)

Conductivity (solid)

None — ions fixed in lattice

Conductivity (liquid/aq)

Yes — ions free to move

Solubility

Usually soluble in water

Exam tip: Never say ionic compounds "contain molecules" — they form a giant ionic lattice of alternating cations and anions. The formula (e.g., NaCl) is the simplest ratio, not a molecule.

Covalent Bonding

Formed by the sharing of electron pairs between non-metal atoms. Each atom contributes one electron to the shared pair. The shared pair is attracted to both nuclei — this electrostatic attraction holds the atoms together.

Types of Covalent Structure

Simple Molecular

Strong covalent bonds within molecules; weak intermolecular forces between them. Low MP/BP. E.g., H₂O, CO₂, I₂

Giant Covalent

Millions of atoms bonded in a continuous network. Very high MP. E.g., diamond (C), silicon dioxide (SiO₂), graphite

Exam tip: When explaining why simple molecular substances have low MPs, say "weak intermolecular forces are broken" — NOT "weak covalent bonds." The covalent bonds within the molecule are strong; it's the forces between molecules that are weak.

Metallic Bonding

Metal atoms lose their outer electrons to form a lattice of positive ions (cations) surrounded by a "sea" of delocalised electrons. The electrostatic attraction between the positive metal ions and the sea of delocalised electrons is the metallic bond.

Melting Point

Generally high (more delocalised e⁻ and higher charge = stronger bond)

Conductivity

Excellent — delocalised electrons carry charge

Malleability

Yes — layers of ions can slide over each other

Alloys

Different-sized atoms disrupt layers, preventing sliding → harder

Exam tip: To explain why transition metals have higher MPs than Group 1: they have more delocalised electrons per atom and smaller ionic radii → stronger metallic bonding. Always link to number of delocalised electrons and ionic charge/size.

Bonding Comparison

Property	Ionic	Simple Covalent	Giant Covalent	Metallic
Particles	Ions	Molecules	Atoms	Cations + e⁻
Bond type	Electrostatic (ion-ion)	Shared pairs	Shared pairs	Electrostatic (ion-e⁻)
Structure	Giant lattice	Discrete molecules	Giant lattice	Giant lattice
Melting point	High	Low	Very high	High (varies)
Electrical conductivity	When molten/dissolved	None	None (except graphite)	Yes (solid & liquid)
Solubility in water	Usually soluble	Varies	Insoluble	Insoluble
Example	NaCl	H₂O, CO₂	Diamond, SiO₂	Fe, Cu

Exam tip: Structure-property questions are worth easy marks. Always: (1) name the structure type, (2) identify the particles, (3) describe the forces/bonds, (4) link to the physical property being asked about. This 4-step approach works every time.