Bonding and structure explains why substances have the properties they do. The answer is always the same chain: which particles are present, which bonds or forces hold them, and what must happen when the substance melts, dissolves or conducts. Check the current syllabus on the Cambridge IGCSE Chemistry 0620 subject page for the exact wording.
The topic links directly to atoms, elements and isotopes, which gives you electron arrangements, and to formulas and equations, where ionic charges become formulas.
What should you know before you start?
You need three ideas.
First, an atom has protons, neutrons and electrons, and the number of protons equals the number of electrons in a neutral atom. Second, you can write an electron arrangement such as 2,8,1 for sodium. Third, you know the position of an element in the periodic table tells you its number of outer electrons.
If any of these is shaky, revisit atoms, elements and isotopes first.
An orienting example
Here is one short question that uses the whole topic. The elements and data are invented for practice.
Element X has electron arrangement 2,8,2 and element Y has 2,7. They form compound XY₂, which melts at 715 °C and conducts only when molten. Explain the structure and these properties.
- X loses 2 electrons to form X²⁺ and each Y gains 1 electron to form Y⁻, so 1 X needs 2 Y. This is the reasoning in explaining ion formation using electrons.
- A high melting point means many strong electrostatic attractions in a giant ionic lattice must be overcome. This is the reasoning in contrasting molecular and ionic melting behaviour.
- It conducts only when molten because the ions can move only then. This is the reasoning in explaining conductivity in solid and molten states.
Notice that each property was explained by naming particles and forces, not by repeating the property.
In which order should you study the lessons?
- Explain ion formation using electrons: electron transfer is the starting point for ionic bonding.
- Represent a simple covalent bond: this adds sharing of electrons and gives you dot-and-cross diagrams.
- Relate a giant structure to a property: diamond, graphite and silicon dioxide show how strong bonds in a lattice control properties.
- Contrast molecular and ionic melting behaviour: this sets weak intermolecular forces against strong ionic attractions.
- Explain conductivity in solid and molten states: it asks whether charged particles are free to move, which uses everything earlier.
Then try the bonding and structure practice set without looking at the lessons.
What are the common traps?
- Naming the wrong bond. Saying covalent bonds break when a molecular substance melts is the most common error. Only intermolecular forces are overcome.
- Forgetting the lone pairs. A dot-and-cross diagram that totals the wrong number of electrons has lost a lone pair.
- Saying “molecule” for a giant structure. Diamond, sodium chloride and silicon dioxide are lattices, not molecules.
- Carrying the wrong particles. Electrons carry charge in metals and graphite. Ions carry charge in molten or dissolved ionic compounds.
- Stopping at the property. “It has a high melting point because it is ionic” repeats the label. The marks are for particles, forces and energy.
How should you use the practice set?
Use the bonding and structure practice set after you have read at least three lessons. Write every answer in full sentences first, then open the solution. Keep a note of which lesson each mistake belongs to with the mistake log and retest queue.
When you later balance formulas and equations, the equation balance reasoning trainer is useful for checking atom counts.
Where does tuition fit in?
Some students understand every lesson but still lose marks because the explanation skips a link in the chain.
A teacher who reads your actual sentences can show which link is missing. That is the heart of online one-to-one Chemistry tuition. You can also look at the wider IGCSE Chemistry learning guide for the other topics.