How do metals obey the octet rule?

Group 1 and Group 2 Metals

Metals in Group 1 can lose one #s# electron to achieve an octet of valence electrons, and metals in Group 2 can lose two #s# electrons to achieve an octet.

Transition Metals (Group 3 to Group 11) and Group 12

Transition metals usually have an electron configuration that ends in #ns^2(n-1)d^x#, where #x = 1, 2, … 9#.

They often lose two or three of their valence electrons, but not enough to get back to an #s^2p^6# configuration.

For example, the electron configuration of #"Fe"# is #["Ar"]4s^(2)3d^6#.

#"Fe"# typically loses 2 electrons to form #"Fe"^(2+)#with configuration #["Ar"] 3d^6#, or #"Fe"^(3+)# with configuration #["Ar"] 3d^5#.

Transition metals will often violate the octet rule by using their #d# orbitals for bonding.

They can expand their octet to twelve or more valence electrons.

An example is hexaamminecobalt(III) chloride.

Groups 13 to Group 15 Metals

Aluminium forms compounds such as #"AlCl"_3#, with an incomplete octet.

All the other metals in Groups 12 to 15 can expand their octets.