Metallic Bonding

Metallic bonding is the electromagnetic interaction between loosely held, delocalized, valence electrons, gathered in an "electron sea", and the metallic nuclei within metals. This type of bonding is seen as the sharing of "free" electrons among a lattice of positively- charged ions (cations).

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Metals have characteristic properties such as: • High thermal and electrical conductivity. • Luster and high reflectivity. • Malleability (They can be beaten or shaped without fracture) • Ductility (They can be drawn and stretched into wire without fracture) • Variability of mechanical strengths (ranging from very soft alkali metals to Tungsten, which is very hard). • Metals generally have low ionization energies. The valence electrons of metal atoms are not strongly held by the nucleus. Thus, metals have free mobile electrons. • Metals have a number of valence orbitals that remain empty as the number of valence electrons in metals is generally less than the number of valence orbitals.

All the characteristic metallic properties can be explained on the basis of the electron.

Metallic Luster: When light falls on the surface of the metal, the loosely held electrons absorb photons of light. They get promoted to higher energy levels (excited state), oscillating at a frequency equal to that of the incoming light. These oscillating electrons readily return from the higher to the lower levels of energy by releasing energy. Light appears to be reflected from metal surface and the surface acquires a shining appearance, which is known as metallic luster.

Electrical conductivity: The presence of mobile electrons causes electrical conductivity of a metal. When a potential difference is applied across a metal, the free mobile electrons in the metallic crystal move toward the positive electrode. The electrons coming from the negative electrode simultaneously replace these electrons. Thus, the metal maintains the flow of electrons from negative electrode to positive electrode. This constitutes electrical conductivity.

Thermal conductivity: When a part of the metal is heated, the kinetic energy of the electrons in that region increases. Since the electrons are free and mobile, these energetic electrons move rapidly to the cooler parts and transfer their kinetic energy by means of collisions with other electrons. Therefore, the heat travels from the hotter to cooler parts of the metal.

Malleability and ductility: Metals can be beaten into sheets (malleability) and drawn into wires (ductility). Metallic bonds are non-directional in nature. Whenever any stress is applied on metals, the position of adjacent layers of metal atoms are altered without destroying the crystal and the metallic lattice gets deformed.