Types of lattices

Most solids are built up with a lattice, with one of a couple of different particles in it. The forces that bind the particles (attraction) can be very different, and determine some properties of that substance.

Metalic lattice
Most metals have strong attraction between the positive metal ions and the negative free electrons in the lattice (see module 3)
Those free electrons can be considered as a kind of glue that holds the ions in there positions in the lattice.
The lattice is in fact the regular arrangement of the metal atoms. In it strong charge forces do rule the result.
Some properties of metals are: metal shine, conductibility for electricity, they are solid (exept Mercury) and often have rather high melting points (not always).

Ionic lattice
In salts are strong attraction forces between positive and negative ions (see module 3).
Those inter ionic forces determine the strength of the lattice and so the melting point. Most important here are the charges of the ions and the distances between them (i.e., they are determined by ionic rays). A strong lattice has small ions with high charges.

Thus, for example MgO has a stronger ionic lattice than NaCl, because the Magnesium and the Oxygen ions are smaller and have more charge than the Sodium and Chloride ions.
Un such an ionic lattice, the positive and the negarive ions are nicely arranged. Inside always the dominat charge forces.
Properties: cristals, high melting points, in molten state they do conduct. the cristals do not conduct electricity!

Molecular lattice
In most liquids and solids the particles are hold toghether by inter molecular attraction forces: In solids, the particles will stay in a molecular lattice. Molecular lattices are stonger when the molecules have more dipole character (a bigger dipole moment), and if they have more mass (are bigger).

In general the attraction forces in molecular lattices are not as strong as in metalic or ionic lattices. So molecular lattices will have lower melting points. In the case of real low attraction forces, they have no lattice at all at normal temperatures, but will be liquid or gas.
Substances with molecular lattice will have covalent bondings between the particles, so mostly built up of non metals.
Exceptions are solids without any lattice structure (amorph) and substances with an atomic lattice, like diamant.

Apart from amorph Carbon, there are two well known lattice structures:
  • diamant with cubic cristals and a density of 3,5
  • graphite with hexagonal cristals and a density of 2.2
Technically it is possible to change graphite into diamant under high pressure. The density can become higher this way.
You can get artificial diamant from graphite.

The molecular lattices are no good conductors; may half conductors.