Intermolecular Forces

Structures of Solids

Structures of Solids

Crystalline solids

Amorphous solids

Unit Cells

The ordered arrangement of atoms, molecules or ions in a crystalline solid means that we can describe a crystal as being constructed by the repetition of a simple stuctural unit.

The crystal structure of sodium chloride

The unit cell of sodium chloride is cubic, and this is reflected in the shape of NaCl crystals

The unit cell can be drawn with either the Na+ ions at the corners, or with the Cl- ions at the corners.

Within the unit cell there must be an equal number of Na+ and Cl- ions.

For example, for the unit cell with the Cl- ions at the center of the faces

Close packing of spheres

Many ions are spherical and many small molecules pack in a crystal lattice as essentially spherical entities.

Spheres can pack in three-dimensions in two general arrangements:

The coordination number is the number of particles surrounding a particle in the crystal structure.

1996 Michael Blaber