Solid Lattices

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Metallic lattices

Metallic Lattices: Composed of a regular arrangement of positive metal ions surrounded by delocalised electrons

Typical properties:

High melting temperature

High boiling temperature

Good electrical conductivity

Good thermal conductivity

Malleability

Ductility

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Giant Ionic Lattices

Ionic lattice: Composed of a regular arrangement of positive and negative ions

Typical properties:

Fairly high melting temperature

Brittle

Poor electrical conductivity when solid but good when molten

Often soluble in water

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Giant Covalent Lattices

Giant covalent lattice: Giant network of atoms liked to each other by covalent bonds

Four most common giant covalent lattices:

Diamond

Graphite

Graphene

Silicon (IV) oxide

Diamond

Giant three dimension tetrahedral arrangement of carbon

Each carbon atom forms four sigma bonds to four other carbon atoms

All bond angles are 109.5°

Extremely hard and high melting temperature e to eat number of strong C-C bonds.

Graphite

Each carbon atom is bonded to three others by sigma bonds

These form interlocking hexagonal rings

Fourth electron on each carbon is in a p orbital

P orbitals overlap with one another to produce a cloud of delocalised electrons above and below the plane of the rings

High melting temperature due to large number of strong C-C bonds

Graphite as a lubricant

Graphite can be used as a solid lubricant as the layers slide easily over each other

Weak London forces between layers

Lubricating properties are also as a result of adsorbed gases on the surface of the carbon atoms

For this reason, graphite will not act as a lubricate in a vacuum and therefore, cannot be used in spacecraft

Graphite as an electrical conductor

Acts as a good electrical conductor as the delocalised electrons between the layers are free to move under the influence of an applied potential difference

Only conducts electrical parallel to its layers as the delocalised electrons are not free to move from one layer to the next

Graphene

One atom thick layer of graphite

Pure carbon in the form of a very thin sheet

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Molecular Lattices

Molecular lattice: A crystal lattice made of molecules bonded together by intermolecular forces.

Examples: Iodine (\(I_2\)), Sulfur (\(S_8\)), White phosphorus (\(P_4\)) (Shown below)

Typical properties:

Low melting and boiling points

Only intermolecular forces need to be overcome, not intramolecular bond

Macromolecular solids have higher melting temperatures than their monomers

London forces tend to increase with increasing chain length and number of electrons

Example: Boiling point of polyethene will be much higher than ethene