This mini-lesson walks you through CCEA Unit 1, sections 1.2 (Bonding) and 1.3 (Structures): the three types of bond (ionic, covalent, metallic), how to draw dot-and-cross diagrams, the four types of structure (giant ionic lattice, covalent molecular, giant covalent, metallic), and how each structure explains a substance's properties.
Make a guess: what changes inside salt when it melts?
Mission 1Why does molten salt light the bulb?
Mission 2How can carbon be both hard and slippery?
Work through each screen, answer the questions as you go (some are wordy, some classify or calculate) and collect ⭐ stars. Press Start when you're ready.
Bond 1 · ionic bonding
Ionic bonding = transfer of electrons
An ionic bond forms between a metal and a non-metal. The metal atom transfers its outer electron(s) to the non-metal. Both atoms end up with a full outer shell, but they are now charged ions:
The metal loses electrons → a positive ion (cation), e.g. Na → Na+.
The non-metal gains electrons → a negative ion (anion), e.g. Cl → Cl−.
Sodium (✕) transfers its one outer electron to chlorine (•). Na becomes Na⁺ (2,8); Cl gains it to become Cl⁻ (2,8,8) with 8 outer electrons.
Watch out: in ionic bonding electrons are transferred, never shared. The "dot-and-cross" just tracks where each electron came from — there is still only one kind of electron.
Quick check
Which ion forms?
?Magnesium is in Group 2 of the periodic table. When magnesium reacts to form an ionic compound, which ion does a magnesium atom become?
Structure 1 · giant ionic lattice
Ions build a giant lattice
Huge numbers of oppositely-charged ions pack together in a regular 3-D giant ionic lattice, held by strong electrostatic attraction in every direction. In sodium chloride each Na⁺ is surrounded by 6 Cl⁻, and each Cl⁻ by 6 Na⁺.
A giant ionic lattice of NaCl. CCEA: you should recognise this structure (drawing it is not required).
Properties explained by the lattice:
High melting & boiling points — lots of energy is needed to break the many strong ionic bonds.
Conducts when molten or dissolved, but NOT when solid — the ions only become free to move (and carry charge) once the lattice breaks down.
Most ionic compounds are soluble in water.
Watch out: a solid ionic compound does not conduct — the ions are locked in place. It only conducts when molten or dissolved, when the ions are free to move.
Identify it
Name the structure from its clues
Read the properties, then tap the structure they describe.
Bond 2 · covalent bonding
Covalent bonding = sharing electrons
A covalent bond forms between two non-metals. Instead of transferring electrons, the atoms share a pair of electrons — one from each atom. A shared pair = one covalent bond.
Water: oxygen (•) shares one pair with each hydrogen (✕) where the shells overlap. Each shared pair is a single covalent bond; oxygen also keeps two lone pairs.
Watch out: covalent = sharing, ionic = transfer. No ions form in a covalent bond, so a single covalent molecule has no overall charge.
Predict it
Predict the bonding
?Methane, CH₄, is made from carbon and hydrogen — both non-metals. What type of bonding holds a methane molecule together?
Structure 2 · covalent molecular
Simple molecular substances
Many covalent substances exist as small, separate molecules — e.g. carbon dioxide (CO₂) and iodine (I₂). The bonds inside each molecule are strong, but the forces between molecules are only weak van der Waals' forces.
Strong covalent bonds (C=O double bonds) hold each CO₂ molecule together; only weak forces act between the molecules.
Properties:
Low melting & boiling points — only the weak van der Waals' forces between molecules need to be broken (so many are gases/liquids at room temperature).
Do not conduct electricity — there are no free charged particles (the molecules are neutral).
Many are insoluble in water.
Mission 1 check
Why does molten salt light the bulb?
?Potassium iodide is an ionic compound. A student puts a solid lump of it in a circuit: the bulb stays off. She melts it and tests again: the bulb lights. What changed?
Mission 2 of 2
How can carbon be both hard and slippery?
Make a guess: how can the same carbon atoms be hard or slippery?
Structure 3 · giant covalent
Giant covalent: diamond & graphite
Some covalent substances are not small molecules — they are giant lattices of a huge number of atoms joined by strong covalent bonds. Carbon forms allotropes (different structures of the same element): diamond and graphite (and graphene). Carbon can form four covalent bonds.
Diamond: each carbon bonded to 4 others in a tetrahedron. Graphite: layers of hexagons, each carbon bonded to 3, with one delocalised electron per atom and weak forces between layers.
Both have very high melting/boiling points (many strong covalent bonds), but they differ:
Diamond — very hard; does not conduct (no free electrons). Used in cutting tools.
Graphite — soft & slippery (layers slide); conducts electricity. Used as a lubricant and in pencils.
Watch out: graphite conducts because each carbon has one delocalised electron (it forms only 3 bonds, using 3 of its 4 outer electrons), free to move and carry charge. Diamond uses all four outer electrons in bonds, so it has no free electrons and cannot conduct.
Explain it
Why does graphite conduct?
?Graphite conducts electricity but diamond does not, even though both are giant covalent forms of carbon. What is the reason?
Allotrope · graphene
Graphene — a single layer
Graphene is a single layer of graphite — one atom thick — with each carbon covalently bonded to three others in hexagons. It is:
Very strong and light (strong covalent bonds, only one atom thick).
A good electrical conductor (one delocalised electron per carbon, as in graphite).
Because it is strong, light and conducts, graphene has many uses — for example in batteries and solar cells. The term allotrope means a different structural form of the same element: diamond, graphite and graphene are all allotropes of carbon.
Link: graphene shares graphite's conducting trick (delocalised electrons) but, as a single sheet held only by strong covalent bonds (no weak forces between layers to slide), it is very strong.
Bond 3 · metallic bonding
Metallic bonding = sea of electrons
In a metal, the atoms lose their outer electrons to become a giant lattice of positive ions sitting in a sea of delocalised electrons. The strong electrostatic attraction between the positive ions and the negative delocalised electrons is the metallic bond.
A giant metallic lattice: a regular arrangement of positive metal ions, with delocalised electrons free to move throughout.
Properties explained by this model:
Good electrical conductors — the delocalised electrons are free to move and carry charge.
Malleable & ductile — layers of ions can slide over each other while the sea of electrons holds them together, so the metal can be hammered into shape or drawn into wire.
High melting & boiling points — much energy is needed to break the strong metallic bonds.
Sort it
Predict the bonding type
Drag each substance into the bonding type its elements give. Tap a chip, then tap a box.
Ionic
Covalent
Metallic
Metals · alloys
Alloys — harder than pure metals
An alloy is a mixture of two or more elements, at least one a metal, and the mixture has metallic properties. The different-sized atoms distort the layers, so the layers can no longer slide over each other easily — making alloys harder than the pure metal.
A bigger (or smaller) atom in the lattice stops the layers sliding cleanly, so the alloy resists deforming.
CCEA example: jewellery gold is an alloy with silver, copper and zinc. Purity is in carats — 24 carat = pure gold; 18 carat = 75% gold (18 ÷ 24 × 100).
Calculate
Your turn — carat gold
1A ring is made of 12 carat gold. What percentage of it is gold? (24 carat = pure gold.)
%
Hint: % gold = (carats ÷ 24) × 100.
Mission 2 check
How can carbon be both hard and slippery?
?A drill bit is tipped with diamond. A stiff lock is eased with graphite powder. Both are pure carbon. Why do they behave so differently?
Linking it up
Structure decides the properties
The whole topic comes down to matching a structure to its properties — especially melting point and electrical conductivity:
Giant ionic lattice — high mp; conducts only when molten/dissolved; usually soluble.
Covalent molecular — low mp; does not conduct; often insoluble.
Giant covalent — very high mp; usually doesn't conduct (graphite/graphene are the exceptions).
Metallic — high mp; conducts (solid or molten); malleable & ductile.
An ionic solid can't conduct; melting or dissolving frees the ions so they can carry charge.Match it
Match structure to property
Tap a structure on the left, then its key property on the right.
Identify it
What structure is it?
?A substance has a high melting point, conducts electricity when molten or dissolved but not when solid, and dissolves in water. What is its structure?
Recap
The points to know
Ionic bond: metal + non-metal — electrons transferred, forming + and − ions.