Structure & Bonding

Understanding how atoms join together and the structures they form is key to explaining the properties of materials. This topic covers different types of bonding, how substances are built, and how this affects their physical and chemical behaviour.

Ions and the Formation of Ions

Ions are charged particles formed when atoms gain or lose electrons to achieve a full outer shell, usually with 8 electrons.

• Metal atoms (on the left of the periodic table) lose electrons to form positive ions (cations).
• Non-metal atoms (on the right of the periodic table) gain electrons to form negative ions (anions).

The group number on the periodic table tells you how many electrons are in the outer shell and how many are gained or lost during ion formation.

Ionic Bonding and Ionic Compounds

Ionic bonding occurs between metals and non-metals. The metal loses electrons to become a positive ion, and the non-metal gains electrons to become a negative ion. The oppositely charged ions are held together by strong electrostatic forces.

You can represent this using dot and cross diagrams to show the transfer of electrons from one atom to another.

How Ionic Compounds Are Formed

For example, sodium (Na) loses one electron to form Na⁺, while chlorine (Cl) gains one electron to form Cl⁻. They combine to form sodium chloride (NaCl).

Giant Ionic Lattice

Ionic compounds form a giant lattice structure — a regular, repeating arrangement of ions held together by strong ionic bonds in all directions. This gives them:

• High melting and boiling points
• The ability to conduct electricity when melted or dissolved (because ions are free to move)

Covalent Bonding and Molecular Substances

Covalent bonds form when non-metal atoms share pairs of electrons to achieve a full outer shell. These shared electrons hold the atoms together.

Simple Molecular Substances

These consist of small molecules like H₂O, CO₂, or O₂. They:

• Have low melting and boiling points (due to weak forces between molecules)
• Don’t conduct electricity (no free electrons or ions)

Polymers

Polymers are long chains of covalently bonded molecules, made from repeating units called monomers. They have:

Strong covalent bonds in the chains

Weak intermolecular forces between chains

Higher melting points than simple molecules but lower than giant covalent structures

Giant Covalent Structures (Macromolecules)

Some substances form giant covalent structures, where all atoms are bonded by strong covalent bonds throughout the structure. These include:

Very high melting and boiling points

Usually don’t conduct electricity (except graphite)

Very hard or strong materials

Allotropes of Carbon

Carbon can form several different structures (called allotropes) because each carbon atom can make four bonds.

Diamond

• Each carbon bonded to 4 others
• Hardest natural substance
• Doesn’t conduct electricity

Graphite

• Each carbon is bonded to 3 others in layers
• Layers slide easily — used as a lubricant
• Conducts electricity due to free electrons

Graphene

• A single layer of graphite
• Strong and light
• Conducts electricity well — used in electronics

Fullerenes

• Molecules of carbon arranged in spheres or tubes
• E.g., Buckminsterfullerene (C₆₀)
• Used in drug delivery, lubricants, and nanotechnology

Metallic Bonding

Metallic bonding occurs in metals. Atoms are arranged in layers of positive ions surrounded by a sea of delocalised electrons. These free-moving electrons allow metals to:

• Conduct heat and electricity
• Be malleable and ductile (layers slide)
• Have high melting and boiling points

The strength of metallic bonding explains why metals are strong and useful for structural materials.

States of Matter and Changing State

Substances can exist in three states: solid, liquid, or gas.

• Solids have fixed shapes and particles in regular patterns.
• Liquids flow and take the shape of their container.
• Gases expand to fill the space and move freely.

Changing from one state to another involves adding or removing energy:

• Melting (solid → liquid)
• Boiling (liquid → gas)
• Condensing (gas → liquid)
• Freezing (liquid → solid)
• Sublimation (solid → gas)

These changes are physical, not chemical — the substance stays the same.

Nanoparticles and Their Uses

Nanoparticles are extremely small particles (1–100 nanometres in size), containing only a few hundred atoms. They have a very large surface area to volume ratio, which gives them unique properties.

Uses of Nanoparticles:

• In sun creams and cosmetics (transparent and effective)
• As drug delivery systems (targeting specific cells)
• In electronics, antibacterial coatings, and catalysts

However, the use of nanoparticles raises concerns about their long-term health and environmental effects, as their small size may allow them to enter the body or environment in unknown ways.

Also see Polymers, The Periodic Table,  Atomic Structure

Links for Learning

Bitesize: Ionic compounds
Bitesize: The three states of matter
Bitesize: Small molecules
Bitesize: Giant covalent molecules
Bitesize: Metals and alloys