1.3 Structure

• conducts electricity when molten, doesn’t conduct electricity when solid (the ions are held in fixed positions in the lattice so cannot move to carry a charge when solid, however when molten the ions are free to move and carry a charge) • high melting and boiling points (large amount of energy is required to break the strong ionic bonds between the ions in the lattice) • soluble in water • is a compound

• low melting and boiling points (a small amount of energy is needed to break the weak van der Waals forces between the molecules • insoluble in water • does not conduct electricity (the molecules are neutral so there are no ions or delocalised electrons to carry a charge)

• high melting point (a large amount of energy is required to break the strong metallic bonds between the positive ions and delocalised electrons) • conducts electricity (delocalised electrons can move and carry a charge) • ductile and malleable (layers can slide over each other without disrupting the bonding)

Diamond, graphene and graphite

GIANT COVALENT STRUCTURE (each carbon is covalently bonded to four other carbon atoms in a tetrahedral 3D structure • high melting and boiling points (a large amount of energy is needed to break the strong covalent bond between the carbon atoms) • doesn’t conduct electricity (diamond has no ions or delocalised electrons that can carry charge) • very hard (strong covalent bonds arranged in a rigid tetrahedral structure) • used for drilling through hard materials like rock and glass

• conducts electricity (has free electrons to carry a charge) • used in batteries and solar cells • a single atom thick layer of graphite (arranged in hexagons) • 100x stronger than steel (due to rigid structure of hexagons and strong covalent bonds) • low density (single layer of atoms)

GIANT COVALENT STRUCTURE (each carbon atom forms three covalent bonds with other carbon atoms, arranged in hexagons, weak forces of attraction between layers caused by delocalised electrons) • conducts electricity (carbon atoms have a free electron which can carry a charge) • high melting and boiling points (a large amount of energy is required to break the strong covalent bonds between carbon atoms) • soft (weak forces between the layers so they can easily slide over each other) • used in pencils and as a lubricant

Different forms of the same element in the same physical state (eg carbon —> graphite, graphene, diamond)

Can be drawn into wires

Can be hammered into shape

A mixture of two or more elements, at least one of which is a metal and the resulting mixture has metallic properties

Too soft

A gold alloy containing silver, copper or zinc

Carats

24

No. Of carats/ 24 x 100

18

The different sizes of atoms in an alloy distort the layers in metallic structure, making it more difficult for them to slide over each other. This means alloys are harder than pure metals

4