For elements that are solid at standard temperature and pressure the table gives the crystalline structure of the most thermodynamically stable form(s) in those conditions. In all other cases the structure given is for the element at its melting point. Data is presented only for the first 112 elements (hydrogen through copernicium; it is not available for any further ones), and predictions are given for elements that have never been produced in bulk (astatine, francium, and elements 100–112).
Contents
Close packed metal structures
Many metals adopt close packed structures i.e. hexagonal close packed and face centred cubic structures (cubic close packed). A simple model for both of these is to assume that the metal atoms are spherical and are packed together in the most efficient way (close packing or closest packing). In closest packing every atom has 12 equidistant nearest neighbours, and therefore a coordination number of 12. If the close packed structures are considered as being built of layers of spheres then the difference between hexagonal close packing and face centred cubic is how each layer is positioned relative to others. Whilst there are many ways that can be envisaged for a regular buildup of layers:
Hexagonal close packed
In the ideal hcp structure the unit cell axial ratio is
Face centered cubic (cubic close packed)
More content relating to number of planes within structure and implications for glide/slide e.g. ductility.
Double hexagonal close packed
Similar to the ideal hcp structure, the perfect dhcp structure should have a lattice parameter ratio of
Body centred cubic
This is not a close packed structure. In this each metal atom is at the centre of a cube with 8 nearest neighbors, however the 6 atoms at the centres of the adjacent cubes are only approximately 15% further away so the coordination number can therefore be considered to be 14 when these are included. Note that if the body centered cubic unit cell is compressed along one 4 fold axis the structure becomes face centred cubic (cubic close packed).