In the metallic bond, most metals crystallize in close- packet structures. There is a strong electron interaction among 8 to 12 nearest neighbour atoms.Also called as coordination number.This develops the ability in metals to conduct electricity and heat.
How Metallic Bond Form
Bonding in metals results from electrical attraction among positive charge metal ions and mobile, delocalized electrons belonging to crystal as a whole.
Explanation of Metallic Bond
We can explain metallic bond with the help of two models.
2.Electron Sea model
The interaction of two atomic orbitals, say 3s- orbitals of two sodium atoms, produces two molecular orbitals, one bonding orbitals and one antibonding orbital. If N atomic orbitals interact, N molecular orbitals are formed. Atoms interact more strongly with nearby atoms than those of farther away. The energy that separates bonding and antibonding molecular decreases the interaction (overlap) between the atomic orbital decreases.
When we consider all the possible interactions among one mole of Na atoms.There is a formation of series of very close spaced molecular orbitals(3σ s and 3σ*s (sigma star)). This consists of a nearly continuous band of orbitals belonging to crystal as a whole. One mole of Na atoms contributes one mole(6.022×10 23 )of Valence Electrons. Thus,6.022×10 23 orbitals in the band are half filled.
The empty 3p atomic orbitals of sodium atoms also interact to form a wide band of 3* 6.0710 23 orbitals.The 3s and 3p atomic orbitals are quite close in energy. So, these bands of a molecular orbital overlap. The two overlapping band contains 4 *6.0710 23 orbitals because each orbital can hold two electrons. The resulting combination of full bands is only one-eighth full.
According to the band theory, the highest energy electrons of metallic crystals occupy either full band or partially band that overlap an empty band. A band within which(or into which) electrons must move to allow electrical conduction we call as conduction band. The electrical conductivity of metal decreases as temperature increases. The increase in temperature causes thermal agitation of metal ions.This impends the flow of electrons when an electric field is applied.
Crystalline nonmetals, such as diamond and phosphorus are insulators. They do not conduct electricity.It is due to the fact that there is highest energy electrons occupy filled bands of molecular orbitals that are separated from the lowest empty band (conduction band) by the energy difference called the band gap.In insulators, this band is in energy different that is too large for him to jump to get the conduction band.
Elements that are semiconductors have filled bands that are only slightly below.They do not overlap with the empty band.They do not allow electricity to pass at low temperature.A small increase in temperature sufficient to excite some of the electrons.The electrons jump into the highest energy band conduction band.
Electron Sea model
Metals have the ability to conduct electricity and heat.Also formation into sheet drawn, into wires and lustrous appearance. One over a simplified model that can account for some of the properties is electron sea model. The metals picture as a network of positive ions immersed in a “sea of electrons”. In Lithium, the ions would be Li+ and one electron per atom would be contribute to sea. These free electrons account for the characteristic metal properties. If metals ends are connect to the external source of electric current.Free electrons from one end cross through metal.Then,leave the other end at the same rate in thermal conductivity in an electron.
By hammering the internal structure remain unchanged as a sea of electrons rapidly adjust to the new situation.
This is about the metallic bond.