Metallic Bond and types|A metallic bond is a bond between

Metallic Bond

Hello friends, welcome to our blog, today we are going to discuss metallic bond. Most metal crystallize in close- packet structures. Strong electron interaction among 8 to 12 nearest neighbour atoms (called as coordination number) develop the ability in metals to conduct electricity and heat.

A metallic bond is a bond between

 Bonding in metals is called as metallic bonding. Bonding in metals result from electrical attraction among  positive charge metal ions and mobile, delocalised electrons belonging to Crystal as a whole.

Two models are considered to explain metallic bonding:

1.Band model
2.Electron Sea model

Band Model.

The interaction of two atomic orbitals, say 3s- orbitals of  two sodium atoms,produces two molecular orbitals, one bonding orbitals and one antibonding orbitals .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 orbitals decreases as 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 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 that 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 fully band or partially band that overlap an empty band. A band within which(or into which) electrons must move to allow electrical conduction is called 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 if it is due to the fact that their 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 insulated ,this band  is in an 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, but do not overlap with empty band.They do not conduct electricity at low temperature but small increase in temperature sufficient to excite some of the electron and jump into the highest energy band conduction band.

Electron Sea model

Metals have ability to conduct electricity, ability to conduct heat, formation into sheet drawn, into wires and lustrous appearance. One over 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 contributed to sea. These free electrons account for the characteristic meal properties. If metals ends are connected to the external source of electric current, one end free electron cross through metal and leave the other end at the same rate in thermal conductivity in electron .

By hammering the internal structure remain unchanged as a sea of electrons rapidly adjust to new situation.

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