Grade 10
Ionic, covalent and metallic bonding
Compare ionic attraction, shared electron pairs and delocalised metallic electrons. Bonding models explain why solids conduct, melt or fracture differently.
IntuitionIntuition: particles and change
Salt crystals shatter, copper conducts electricity, and wax melts at low temperature. Their structures differ because atoms and ions are held together in different ways.
SchoolSchool: models and rules
Definition: Key idea
An ionic solid is held by electrostatic attraction between oppositely charged ions; a covalent bond shares electron density between atoms; a metallic solid has delocalised valence electrons binding positive atomic cores.
Sodium chloride is an ionic lattice, not a set of isolated NaCl molecules. Electron transfer is a useful bookkeeping model: the crystal’s stability comes from attraction throughout the lattice.
| Bond type | How it holds atoms | Typical properties |
|---|---|---|
| Ionic | attraction between opposite ions | brittle; conducts when molten or dissolved |
| Covalent | shared electron pairs | molecular solids soft; networks very hard |
| Metallic | delocalised electrons bind cation lattice | conducts as solid; malleable |
Example: Worked example
Why does solid sodium chloride not conduct but molten sodium chloride does?
Solution
In the solid lattice, ions are fixed and cannot carry charge through the material. In the melt, ions can move and transport charge.
Example: Second example
Which conducts electricity as a solid: copper, NaCl crystal, or dry sugar?
Solution
Only copper: metallic bonding gives mobile electrons that carry charge. NaCl conducts only when melted or dissolved; sugar does not conduct.
Covalent bonds form molecules such as H₂O or extended networks such as diamond. Metals conduct because mobile electrons respond to an electric field; ionic solids conduct when ions are mobile in a melt or solution.
Which model applies depends on the atoms involved and their electronegativities: NaCl is ionic, H₂O covalent, Cu metallic. Real bonding is a continuum between these ideal cases.
UndergraduateDeeper view
At a deeper level, classify observations by the particles involved and by the quantities that remain invariant. Models describe charge, electron density or particle counting; choose the simplest model that accounts for the measured evidence.
Example: Calculation / application example
Rank the bond character of Cl–Cl, C–H, and Na–Cl from least ionic to most ionic.
Solution
Cl–Cl (Δχ = 0, non-polar covalent) < C–H (Δχ ≈ 0.35, weakly polar covalent) < Na–Cl (Δχ ≈ 2.2, predominantly ionic).