How to Study Bonding and Structure for IGCSE Chemistry

Bonding and structure is the topic that explains why substances behave the way they do. Why does sodium chloride have a high melting point? Why does diamond not conduct electricity? Why is copper malleable? Every answer comes back to the type of bonding and the structure of the substance. This topic underpins almost every other topic in the syllabus, which is why it appears early in the course and keeps reappearing in questions about metals, organic chemistry, and electrochemistry.

The three types of bonding

Ionic bonding

Ionic bonding occurs between a metal and a non-metal. The metal atom loses electrons to form a positive ion (cation), and the non-metal atom gains electrons to form a negative ion (anion). The oppositely charged ions are held together by strong electrostatic attraction.

Dot-and-cross diagrams for ionic compounds: Show the electron transfer. The metal atom’s outer electrons move to the non-metal. Draw square brackets around each ion with the charge written outside.

Key examples to practise: NaCl (1 electron transferred), MgO (2 electrons transferred), MgCl2 (2 electrons transferred, one to each Cl), CaF2.

Properties of ionic compounds:

• High melting and boiling points (strong electrostatic forces between ions require a lot of energy to overcome)
• Conduct electricity when molten or dissolved (ions are free to move and carry charge) but not when solid (ions are fixed in the lattice)
• Usually soluble in water
• Brittle (when a force is applied, layers of ions shift, like charges align, and the structure shatters due to repulsion)

Covalent bonding

Covalent bonding occurs between non-metal atoms. Atoms share pairs of electrons so that each atom achieves a full outer shell. The shared pair of electrons is attracted by both nuclei, holding the atoms together.

Dot-and-cross diagrams for covalent compounds: Show the shared pairs between atoms. Use dots for one atom’s electrons and crosses for the other.

Key examples: H2 (single bond), O2 (double bond), N2 (triple bond), H2O, NH3, CH4, CO2, HCl, C2H4 (ethene, with a C=C double bond).

Two types of covalent structure:

Simple molecular: Small discrete molecules held together by weak intermolecular forces. Properties: low melting and boiling points (weak intermolecular forces are easy to overcome), do not conduct electricity (no charged particles free to move), often insoluble in water. Examples: H2O, CO2, CH4.

Giant covalent: Millions of atoms bonded in a continuous network. Properties: very high melting points (many strong covalent bonds must be broken), do not conduct electricity (except graphite), insoluble. Examples: diamond (each C bonded to 4 others, tetrahedral), graphite (each C bonded to 3 others in layers, with delocalised electrons between layers — conducts electricity), silicon dioxide.

Metallic bonding

Metal atoms lose their outer electrons to form a “sea” of delocalised electrons. The positive metal ions are held in a regular lattice by the attraction to this electron sea.

Properties of metals:

• Good conductors of electricity and heat (delocalised electrons carry charge and energy)
• Malleable and ductile (layers of ions can slide over each other without breaking the bond, because the electron sea holds them together in the new position)
• High melting points (generally, but varies — strong metallic bonds require energy to break)

How to study this topic

Phase 1: Learn to draw (3 days)

Bonding is visual. You must be able to draw dot-and-cross diagrams accurately and quickly. Practise the full set of required diagrams from memory:

Ionic: NaCl, MgO, MgCl2, CaF2 Covalent: H2, Cl2, O2, N2, H2O, NH3, CH4, CO2, HCl, C2H4

Draw all of them, check against the textbook or diagram guide, then redraw the ones you got wrong. Repeat the next day. By day 3, you should be able to draw any of them in under 30 seconds.

Phase 2: Learn the property explanations (4 days)

The exam does not just ask what the properties are. It asks why. “Sodium chloride has a high melting point” earns zero marks. “Sodium chloride has a high melting point because there are strong electrostatic forces of attraction between the oppositely charged ions, and a lot of energy is needed to overcome these forces” earns two marks.

For each structure type, write the property explanations from memory:

• Why does it have a high/low melting point?
• Why does it conduct/not conduct electricity?
• Why is it soluble/insoluble?
• Why is it hard/soft/malleable/brittle?

Check your explanations against the mark scheme language. Precision matters. “The bonds are strong” is vague. “Strong electrostatic forces between oppositely charged ions” is specific and scores.

Phase 3: Compare structures (2 days)

Build a comparison table:

Property	Ionic	Simple molecular	Giant covalent	Metallic
Melting point	High	Low	Very high	High (varies)
Electrical conductivity	When molten/dissolved	No	No (except graphite)	Yes
Solubility in water	Usually yes	Varies	No	No

Then add the “why” for each cell. This table is your revision summary for the entire topic.

Phase 4: Graphite and diamond (1 day)

Graphite and diamond are favourite exam questions because they have the same element (carbon) but different structures and properties. Study the contrast:

• Diamond: 4 bonds per C, tetrahedral, very hard, does not conduct (no free electrons)
• Graphite: 3 bonds per C, layered, soft and slippery (layers slide), conducts electricity (delocalised electrons between layers)

Draw both structures from memory and explain each property.

Phase 5: Past papers (ongoing)

Bonding questions are predictable. They ask for a dot-and-cross diagram, a property explanation, or a “use the structure to explain” question. Practise these from the bonding and structure exam guide.

Common exam errors

• Saying “covalent bonds are weak” when explaining low boiling points of simple molecular substances. The correct explanation refers to weak intermolecular forces, not weak covalent bonds.
• Drawing dot-and-cross diagrams without showing the correct number of electrons in the outer shell.
• Forgetting to draw square brackets and charges on ionic dot-and-cross diagrams.
• Saying metals conduct because “metal bonds are strong.” They conduct because of delocalised electrons.
• Confusing giant covalent and simple molecular. CO2 is simple molecular (small discrete molecules). SiO2 is giant covalent (continuous network). The exam tests whether you can classify and explain the difference.