Ionic transfer, covalent sharing, metallic seas — understand WHY substances behave the way they do! ⚛️
Ionic bonding occurs between a metal and a non-metal. The metal atom loses electrons to form a positive ion (cation); the non-metal atom gains those electrons to form a negative ion (anion). Oppositely charged ions attract each other strongly.
| Compound | Ions Formed | Electron Transfer | Formula |
|---|---|---|---|
| Sodium chloride | Na⁺ + Cl⁻ | Na loses 1 e⁻ to Cl | NaCl |
| Magnesium oxide | Mg²⁺ + O²⁻ | Mg loses 2 e⁻ to O | MgO |
| Calcium chloride | Ca²⁺ + 2Cl⁻ | Ca loses 2 e⁻; 1 to each Cl | CaCl₂ |
Covalent bonding occurs between two non-metals. Atoms share pairs of electrons so that each atom achieves a full outer shell. Each shared pair is one covalent bond.
| Molecule | Bond Type | Shared Pairs | Outer Shell Electrons Each Atom Achieves |
|---|---|---|---|
| H₂ | Single bond (H−H) | 1 | 2 (like He) |
| HCl | Single bond | 1 | H=2, Cl=8 |
| H₂O | 2 single bonds | 2 | O=8, H=2 |
| NH₃ | 3 single bonds | 3 | N=8, H=2 |
| CH₄ | 4 single bonds | 4 | C=8, H=2 |
| Cl₂ | Single bond (Cl−Cl) | 1 | 8 |
| CO₂ | 2 double bonds (C=O) | 2 per bond | C=8, O=8 |
| N₂ | Triple bond (N≡N) | 3 | 8 |
Some covalent substances form huge networks of atoms all bonded together — these are giant covalent (macromolecular) structures. They have very high melting points because you must break many strong covalent bonds.
| Property | Diamond | Graphite |
|---|---|---|
| Element | Carbon | Carbon |
| Structure | Each C bonded to 4 others in a rigid 3D lattice | Layers of hexagonal rings; each C bonded to 3 others |
| Bonds per C | 4 (all used in bonding) | 3 (1 delocalised electron per C) |
| Melting point | Very high (~3550°C) | Very high (~3600°C) |
| Hardness | Hardest natural substance | Soft and slippery |
| Electrical conductivity | Does NOT conduct | Conducts (delocalised electrons) |
| Why hardness? | Rigid 3D network — no layers to slip | Layers can slide — weak forces between layers |
| Uses | Cutting tools, jewellery | Pencils, electrodes, lubricant |
In metals, atoms release their valence electrons into a "sea" of delocalised electrons that are free to move throughout the metal. The positive metal ions (cations) are held together by their attraction to this electron sea.
| Property | Explanation |
|---|---|
| Good electrical conductor | Delocalised electrons carry charge and move freely |
| Good thermal conductor | Free electrons transfer kinetic energy quickly |
| High melting/boiling point | Strong attraction between cations and electron sea |
| Malleable (can be hammered flat) | Layers of ions can slide without breaking the bond (electron sea adjusts) |
| Ductile (can be drawn into wire) | Same reason — layers slide, electron sea maintains bonding |
| Shiny/lustrous | Delocalised electrons absorb and re-emit light |
| Property | Ionic | Simple Covalent | Giant Covalent | Metallic |
|---|---|---|---|---|
| Particles | Positive & negative ions | Molecules | Atoms (network) | Cations + electron sea |
| Force holding together | Electrostatic attraction | Shared electrons (+ weak intermolecular) | Shared electrons (covalent bonds) | Attraction to e⁻ sea |
| Melting point | High | Low | Very high | High |
| Conducts electricity? | Molten/dissolved only | No | No (diamond) / Yes (graphite) | Yes (solid & liquid) |
| Solubility in water | Often soluble | Variable | Insoluble | Insoluble |
| Examples | NaCl, MgO, CaCl₂ | H₂O, CO₂, NH₃, CH₄ | Diamond, graphite, SiO₂ | Na, Fe, Al, Cu |
Select a molecule to see its dot-and-cross diagram drawn on the canvas. Dots (●) = electrons from one atom; Crosses (×) = electrons from the other atom.
See how bond type determines melting point. The chart animates when this tab opens.
Click the card to flip!
Problem: Compound X is formed from calcium (Group II) and chlorine (Group VII). (a) Predict the type of bonding. (b) Determine the formula. (c) State whether it conducts electricity as a solid. (d) Predict its melting point (high or low?) and explain why.
Type your answer (or type show to reveal):
Calcium is a metal (Group II). Chlorine is a non-metal (Group VII). What type of bonding forms between a metal and a non-metal? (one word)
Calcium is Group II → forms Ca²⁺. Chlorine is Group VII → forms Cl⁻. How many Cl⁻ ions are needed to balance one Ca²⁺? What is the formula of this compound?
In ionic solids, are the ions free to move? Can electricity flow? Type "yes" or "no".
CaCl₂ is ionic. Think about the force holding the lattice together. Is it strong or weak? Does this mean the melting point will be high or low? Type "high" or "low".
Click a term, then click its matching description. Green = correct!
1 (a) Sodium loses 1 electron; chlorine gains 1 electron. ✓ Oppositely charged ions (Na⁺ and Cl⁻) are formed. ✓ Strong electrostatic attraction between ions holds them in a lattice. ✓
2 (b) A large amount of energy is needed to overcome the strong electrostatic attraction between Na⁺ and Cl⁻ ions in the ionic lattice. ✓
3 (c) When molten (melted) — ions are free to move. ✓ When dissolved in water (aqueous solution) — ions are free to move. ✓
1 (a) H₂O: O in centre with 2 bonding pairs to H and 2 lone pairs. ✓ Each H has 2 electrons in outer shell (including shared pair). ✓ O has 8 electrons (2 lone pairs + 2 bonding pairs). ✓
2 (b) NH₃: N in centre with 3 bonding pairs to H atoms and 1 lone pair. ✓ Each H has 2 electrons. ✓ N has 8 electrons (1 lone pair + 3 bonding pairs). ✓
Award marks for correct structure even if representation style differs. Lone pairs must be shown for full marks.
1 Diamond: each C bonded to 4 others in a rigid 3D tetrahedral lattice ✓; graphite: layers of hexagonal rings, each C bonded to 3 others ✓.
2 (a) Diamond is extremely hard because its rigid 3D network of strong covalent bonds cannot be broken by sliding. ✓ Graphite's layers can slide over each other (only weak forces between layers), so it is soft and not suitable for cutting. ✓
3 (b) In graphite, each C uses only 3 of its 4 valence electrons in bonding — the 4th becomes a delocalised electron free to move through the layers and carry charge. ✓ In diamond, all 4 valence electrons are used in covalent bonds — there are no free electrons available to conduct electricity. ✓
1 Metal atoms release their valence electrons into a "sea" of delocalised electrons. ✓
2 These delocalised electrons are free to move throughout the metal structure. ✓
3 When a voltage is applied, electrons flow from negative to positive terminal — this constitutes an electric current. ✓
4 In both solid and liquid states, the delocalised electrons remain free to move (the metal cations are present in both states), so conduction occurs in both. ✓
1 X is a simple molecular (covalent) substance. ✓
2 Reason 1: Very low melting point (−85°C) indicates only weak intermolecular forces between molecules — typical of simple covalent substances. ✓
3 Reason 2: Does not conduct in any state — no charged particles (no ions and no free electrons). ✓
4 Award 1 additional mark if student correctly distinguishes from giant covalent (which would also be non-conducting but has a very HIGH m.p.) ✓
Metal → loses e⁻ → cation (+)
Non-metal → gains e⁻ → anion (−)
Non-metal + Non-metal → share e⁻
Single=1 pair, Double=2, Triple=3
Ionic: molten/dissolved only
Covalent: never
Metallic: always
Diamond: 4 bonds, rigid, non-conducting
Graphite: 3 bonds, layers, conducts
Cations + delocalised electron sea
Malleable, ductile, conducts
Simple cov. < Ionic ≈ Metallic
< Giant covalent (highest)