Key Notes
Crystals and glasses A crystalline solid is characterized by a unit cell containing an
arrangement of atoms repeated indefinitely; noncrystalline or glassy
solids do not have a unit cell. Short-range order resulting from the
local bonding of atoms may, however, be similar in crystals and glasses.
Looking at unit cells Different representations of unit cells are possible. It is important to
understand how to use them to determine the stoichiometry of the
compound and the coordination of each atom.
Nonstoichiometry Some solids, especially natural minerals and transition metal
compounds, are nonstoichiometric with variable composition.
Chemical classification The classification of solids into molecular, metallic, covalent
(polymeric) and ionic types is useful provided it is recognized that
there are no hard boundaries between them.
Related topics Electronegativity and bond
type (B1)
Methods of characterization
(B7)