Section 1 of 8Ions and Ionic Bonds
1
Metals lose electrons to form positive ions (cations); non-metals gain electrons to form negative ions (anions).
2
Ions formed from Groups I, II, VI and VII have noble-gas configurations, e.g. Na+ and F– both have 2,8 like neon.
3
An ionic bond is the strong electrostatic attraction between oppositely charged ions; it acts in all directions.
4Dot-and-cross diagrams
Dot-and-cross diagrams show only the outer shells (or all shells if asked), use square brackets and charges, and show transferred electrons as a different symbol.
5
In NaCl one electron transfers; in MgCl2 the Mg atom gives one electron to each of two Cl atoms; in Na2O two Na atoms each give one electron to one O atom.
6
Ionic compounds have high melting and boiling points because of the many strong attractions throughout the lattice.
7
Ionic compounds do not conduct when solid (ions fixed) but conduct when molten or dissolved (ions mobile). Electrons do not move through the ionic compound.
8
Many ionic compounds dissolve in water but not in organic solvents such as hexane.
9
(Supplement) The giant ionic lattice is a regular 3D arrangement of alternating positive and negative ions (e.g. NaCl is cubic).
10
(Supplement) Dot-and-cross diagrams should be extendable to any metal/non-metal combination, e.g. AlF3, CaO, Li3N.
Section 2 of 8Process & sequence
- Write the electronic configurations of the metal and non-metal atoms.
- Work out how many electrons the metal must lose to reach a full outer shell.
- Work out how many electrons the non-metal must gain to reach a full outer shell.
- Balance the numbers so electrons lost = electrons gained (this gives the formula).
- Draw the ions in square brackets with outer shells: crosses for metal electrons transferred, dots for non-metal electrons.
- Write the charge at the top right of each bracket.
Formation of sodium chloridewrite these steps in this order; each step is a marking point.
- Sodium atom 2,8,1 and chlorine atom 2,8,7 meet.
- Sodium transfers its one outer electron to chlorine.
- Sodium becomes Na+ (2,8); chlorine becomes Cl– (2,8,8).
- Oppositely charged ions attract strongly (ionic bond).
- Many ions arrange into a giant lattice of alternating Na+ and Cl–.
Section 3 of 8Compare
| Group | Electrons lost/gained | Ion charge | Example |
|---|---|---|---|
| I | Lose 1 | +1 | Na+, K+ |
| II | Lose 2 | +2 | Mg2+, Ca2+ |
| III | Lose 3 | +3 | Al3+ |
| V | Gain 3 | –3 | N3– |
| VI | Gain 2 | –2 | O2–, S2– |
| VII | Gain 1 | –1 | F–, Cl– |
| Property | Explanation |
|---|---|
| High melting/boiling point | Strong electrostatic attraction between oppositely charged ions in a giant lattice needs lots of energy to overcome |
| Conduct when molten or aqueous | Ions are free to move and carry charge |
| Do not conduct when solid | Ions are in fixed positions in the lattice and cannot move |
| Often soluble in water | Water molecules attract and separate the ions |
| Feature | What to draw |
|---|---|
| Electron symbols | Dots for one atom, crosses for the other |
| Shells shown | Only the outer-shell electrons |
| Brackets | Square brackets around each ion |
| Charge | Written at the top right, outside the bracket |
| Overall charge | The total positive charge equals the total negative charge, so the compound has no overall charge |
Section 4 of 8Worked examples
Worked examples
Deduce the formula of the ionic compound formed between aluminium and chlorine.
- Al is in Group III → Al3+; Cl in Group VII → Cl–. Charges must balance: 1 × (+3) = 3 × (–1). Formula: AlCl3.
Describe, in terms of electrons, the formation of calcium oxide.
- Ca (2,8,8,2) loses its 2 outer electrons → Ca2+ (2,8,8).
- O (2,6) gains these 2 electrons → O2– (2,8).
- The oppositely charged ions are held by strong electrostatic attraction: CaO.
6 electrons
(Supplement) Deduce the formula of magnesium nitride and state the total number of electrons transferred per formula unit.
- Mg2+ and N3–.
- Lowest common multiple of 2 and 3 = 6: 3 Mg2+ (+6) and 2 N3– (–6).
- Formula Mg3N2;
- 3 × 2 = 6 electrons transferred.
Section 5 of 8Keep going
Ions & Ionic Bonds IGCSE Chemistry 0620: what to do next
These Ions & Ionic Bonds IGCSE Chemistry 0620 notes covered the key ideas, worked examples and exam technique for this topic. Check your Ions & Ionic Bonds IGCSE Chemistry 0620 understanding with the practice questions below, then reread any Ions & Ionic Bonds IGCSE Chemistry 0620 point you were unsure about before moving on.
Ions & Ionic Bonds IGCSE Chemistry 0620: revision checklist
- Revise the main Ions & Ionic Bonds IGCSE Chemistry 0620 definitions until you can write them from memory.
- Practise Ions & Ionic Bonds IGCSE Chemistry 0620 exam questions under timed conditions.
- Link each Ions & Ionic Bonds IGCSE Chemistry 0620 idea to a diagram or a worked example.
- List the common Ions & Ionic Bonds IGCSE Chemistry 0620 mistakes and how to avoid them.
- Explain one Ions & Ionic Bonds IGCSE Chemistry 0620 idea out loud as if teaching a friend.
- Practice: Ions & Ionic Bonds IGCSE Chemistry 0620 practice questions
- Previous lesson: 2.3 Isotopes — 0620 Notes
- Next lesson: 2.5 Simple Molecules & Covalent Bonds — 0620 Notes
- Course: Cambridge IGCSE Chemistry 0620 — all units
- Official syllabus: Cambridge IGCSE Chemistry 0620 syllabus
Section 6 of 8Key terms
Section 7 of 8Command terms
Command terms
State / Name
Give a short answer only; no explanation is needed (1 mark = 1 fact).
Define
Give the precise meaning. Learn the syllabus definitions word-for-word: every keyword in the definition is a marking point.
Describe
Say what happens / what the data show, with key features and figures. Do not give reasons.
Explain
Give reasonswhat happens AND why/how, linked with “because”, “so”, “therefore”.
Suggest
Apply knowledge to an unfamiliar situation; any sensible, scientifically-based answer can score.
Compare
Give similarities AND differences, each as a direct comparison (“X is … whereas Y is …”).
Outline
Set out the main points briefly.
Calculate
Work out from given facts; show working, give the unit and the requested significant figures.
Identify
Name/select from given information.
Predict
Give an expected result without a full justification.
Evaluate
Judge the importance or quality of the evidence/method, with reasons.
Section 8 of 8Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Ion · Cation · Anion · Ionic bond · Ionic compound · Giant ionic lattice · Electron transfer · Noble gas configuration · Dot-and-cross diagram · Electrical conductivity (ionic) · Melting point (ionic) · Solubility (ionic)
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
1
Use the exact scientific term and learn syllabus definitions word-for-word.
2
Write “rate of … increases”, not “… increases”.
3
Say “concentration gradient”, never just “gradient”; name particles precisely (atoms, molecules, ions) — never “it”.
4
Give units with every numerical answer and use the significant figures asked for; show all working.
5
Compare = a similarity AND a difference; describe = what happens; explain = why it happens.
6
Repeats let you identify anomalies and calculate a mean — they do not make an experiment “valid”.
Words to avoid
1
sodium chloride moleculessodium chloride has a giant ionic lattice (no molecules).
2
ionic compounds conduct because electrons movethey conduct when molten/aqueous because ions are free to move and carry charge.
3
the atoms share electrons in NaClan electron is transferred from sodium to chlorine.
4
ionic bonds are weak intermolecular forcesionic bonds are strong electrostatic attractions between oppositely charged ions.
5
chlorine gains an electron to become Cl+chlorine gains an electron to become the chloride ion Cl–.