Structures of solids

Structures of simple solids

The majority of inorganic compounds exist as solids and are made up of ordered arrays of atoms,ions or molecules. Some of the simplest are metals- the structures can be describes in terms of regular, space filling arrangements of all metal atoms. The Metal centres can interact through metallic bonding.

In ionic bonding ions of different elements are held together in symmetrical arrays as a result of attraction between oposite charges (Cations and anions).

Ionic and metallic bonding are non-directional, so structures where these types of bonding occur, are most easily understood in terms of space-filling models that maximise the number and strength of electrostatic interactions between ions. The regular array of atoms/ions/molecules in solids   that produce these structures are best represented in terms of the repeating units that are produced as a result of the efficient methods of filling space. (Covalent bonding is directional-this happens as one of the atoms is more electronegative than the other and pulls the electrons closer in that direction towards it).

The description of the structures of solids

Arrangements of atoms/ions in siple solid structures can be represented by hard spheres. Spheres used in metallic bonding are neautral atoms and spheres used in ionic solids represent cations and anions.

Crystal of an element/compound can be thought of as constructed from a regular repeating structures-atoms/molecules or ions.

A lattice is a 3-D infinte array of points. 

Unit cell is an imaginary parrallelpiped region from which the entire crystal can be built up. Unit cells can be chosen in a variety of different positions but the smallest cell with greatest symmetry is most preferably chosen.

The relationship between lattice parameters in 3 dimensions as a result of the greatest symmetry of the structure gives rise to 7 different crystal systems:

A primitive cell contains one lattice point. Body centre contains two and Face centred contains 

You can work out lattices point using the following rules:

1)A lattice point fully inside…