METALLIC BOND

The constituent particles of metals held together by the bonds called metallic bonds. In fact, more than 80 elements in the periodic table are metals. Except mercury and gallium which are liquids, all other metals are solids at ordinary temperature and pressures.

Nature of bonding in metals

The bonding among metal atoms cannot be ionic, covalent or van der Waal’s type, as explained below.

• Taking the example of lithium, having valance electron 1 i.e. it has only one valence electron. Hence the possibility of its forming electron pair covalent bonds with eight other atoms is ruled out.
• Presence of only one kind of atoms in a metal without any electronegativity difference rules out the possibility of ionic bonding.
• The fact that the metals are quite strong rules out the possibility of their being held together by the weak van der Waal’s forces.

Electron sea model or Electron gas model

According to this model, as metals have low ionization energy, their valence electrons are held very loosely i.e., they are almost like free electrons.

All atoms contribute to form a pool of electrons, which is mobile. Leaving the valence electrons, the remainder portion of the metal atom is a positive ion called “kernel”. For example, in lithium each atom contributes are valence electron to the pool leaving behind Li+ ions; in case of Mg, each atom contributes two valence electron to the pool leaving behind Mg2+ ions. These positive ions or kernels are held in the three dimensional space in a definite pattern in the sea of mobile electrons. This model is called electron gas model because the electrons are free to move in all directions like the molecules of a gas.

The simultaneous attraction between the kernels and the mobile electrons which holds the kernels together is called the metallic bond.