The metallic bonding originates from the sharing of variable number of electrons by a variable number of atoms. Elements of groups I, II and III of periodic table, which have small number of loosely held valence electrons can form metallic bonds. The metallic bonding occurs when each of the atoms of the metal contributes its valence electrons to the formation of an electron cloud which pervades the solid metal.
The electron cloud or also known as electron gas formed by the release of loosely held
electrons, spreads throughout the space occupied by the atoms of the elements. In this electron cloud, valence electrons are not bonded directly to an individual atom or a pair of atoms, but they are free to move in the sphere of influence of other atoms and are bound to different atoms at different times and that also only for a short duration of time.