Metallic elements

A high proportion of metallic elements contain one of the three structures bcc, ccp or hcp just explained. The issues that determine the structure are subtle. In some examples the thermodynamically stable structure relies on pressure and/or temperature, depicting  that the energy variations among them are very small. However, several regularities are observed in the periodic table that suggests that stability depends in a systematic way on the number of valence electrons. The common most stable structures according to group number are

1: bcc               2: varied                      3, 4: hcp

5, 6: bcc           7, 8: hcp                      9-11: fcc

Though, there are irregularities. In the transition metal groups 7, 8 and 9 the 3d series elements Mn, Co and Fe are exceptions. Several elements also have more complex structures, particularly in the p block. An understanding of the issues controlling metallic structures needs the band theory of delocalized electrons.