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2.2 How Bonding and Structure are Related to the Properties of Substances …
2.2 How Bonding and Structure are Related to the Properties of Substances
Properties of ionic compounds
High melting and boiling points
Strong electrostatic forces between ions
Lots of energy needed to break forces
Conduct electricity when molten or aqueous
Ions are free to move to carry charge
Properties of covalent compounds
Polymers
Relatively strong intermolecular forces
Solids at room temperature
Small molecules
Do not conduct electricity
No charged particles
Weak intermolecular forces
Low melting and boiling points
Intermolecular forces get stronger as the molecule gets bigger
Giant covalent structures
Solids at room temperature
E.g. diamond, graphite, silicon dioxide
Very high melting points
Strong covalent bonds between atoms
Bonds must be broken to melt the solid
Properties of metals and alloys
Conductors of electricity
Delocalised electrons carry charge
Strong metallic bonding
High melting and boiling points
Atoms arranged in regular layers
Malleable as the layers slide over each other
Pure metals often too soft
Alloys
Distortion of layers
Makes alloys harder
States of matter
Particle theory
Solid: strong forces and fixed positions
Liquid: no fixed shape, weak forces and free to move
Gas: no fixed shape, very weak forces and particles spaced far apart
State symbols
(s), (l), (g), (aq)
Limitations of simple model
Particles represented as solid spheres with no forces between them
Melting, boiling, condensing, freezing
Energy required to change state
Amount depends on strength of forces between particles