Chemistry

Metallic Bonding
The bonding which holds the metal atoms firmly together on account of force of attraction between metal ions and the mobile electron is called metallic bonding.

X-rays analysis of metal crystal has revealed that each atom in metal crystal is surrounded by 8 or 12 other metal atoms. In metal atoms, the valency electrons are few (1, 2, and 3) and thus, it is not possible for a metal atom to form 8 to 12 covalent bonds with neighbouring atoms. Thus, it was assumed that the atoms in metal crystal are bonded with each other with a special type of bonding known as metallic bonding.
Drude in 1900 proposed the theory of metallic bonding which was later on modified by Lorentz. According to these authors, metals having 1, 2 or 3 electrons in outermost shells, being electropositive lose their electron readily because of low IE values to form free electrons and remainder portion of atom with a Kernel (core of stable nature) carrying positive charge. The free electrons are mobile in nature and move from the one Kernel to another which are closely packed in regular fashion throughout the crystal lattice. thus, the metal crystal is represented by an arrangement of positively charged Kernels in a sea of mobile electrons (Figure) shared by each Kernal to give metallic bonds. Ad the shared electrons are delocalized, the metallic bonds have neither direction nor saturation. There are two essential conditions for metallic bonding :
1. The metal atoms should have low ionization energy.
2. There should be sufficient number of vacant orbitals.
The strength of metallic bonds increases with increase in :
(i) Number of valence electrons
(ii) Charge on the nucleus.
It is therefore, explained that alkali metals are soft and have low melting point, boiling point in comparison to transition metals which are hard and have high m.p., b.p. since, transition metals possess higher number of valence electrons as well as the higher charge on nucleus.
It is metallic bonding which explains the electrical and thermal conductance, metallic luster, malleability, ductility m.pt., b.pt., hardness in metals.