Calcium ion and bromide ion would form Calcium bromide. Potassium ion and sulfide ion would form Potassium sulfide. Aluminum ion and selenide ion would form Aluminum selenide. Metallic bonds form between metal cations through a "sea of electrons" shared between all the metal atoms. Metals are ductile and good conductors of electricity due to the free movement of delocalized valence electrons between metal cations. Alloys can have superior properties to their component elements.