Metallic Bonding

We have noticed in covalent bonding, that non-metals have sufficient number of valence electrons to combine and form molecules by sharing of electron pairs with one another. For example two chlorine atoms share an electron pair in Chlorine (Cl2) molecule.

However most of the metal atoms have less than four valence electrons (many metals have only one or two). These electrons are not confined to any particular atom, instead they move freely from one atom to another atom. Hence the atoms should be considered to be positively charged ions; therefore, metal is defined as: A substance consisting of positively charged ions, fixed in a crystal lattice with negatively charge electrons moving freely through the crystal. Therefore free electrons act as cohesive force which hold the atoms together and form a metallic bond.

Metallic bond is defined as the combination of electrostatic attraction between the electrons and the positive nuclei of atoms. X-rays analysis reveals that metal particles are held together in a lattice of closely packed spheres.

A survey of the observed properties of metals indicates that the nature of force, holding the atoms together in a crystal, must be unusual. Metals are ductile (easily converted into thin wires) and malleable (easily bent or hammered into sheets).

They are good conductors of both heat and electricity (in solid or liquid states), they appear shiny and lustrous. Metals Eire solids at room temperature (except mercury (Hg)). They can be mixed with metals or non-metals to yield alloys with variable properties. All of these properties are because of peculiar bonding i.e. metallic bonding.

The strength of metallic bond varies considerably among different metals. Thus it is much stronger in iron than in sodium or potassium.

5.7.1 Metallic Binding in Sodium: (Na)

Sodium (Na) metal has one valence electron per atom. It crystallizes in a body centered cubic structure, in which each sodium is surrounded by eight nearest neighbors’. These valence electrons are not confined to any particular atom, instead, they are free to move throughout the crystal, so the resulting bond is relatively weak, that is, why metals like sodium and potassium are soft and have relatively low melting points.

5.7.2 Metallic Bonding in Iron (Fe) and Copper (Cu):

The metals iron (Fe) and copper (Cu) are hard and have high melting points because; these metals have incomplete valence shells. Therefore, the atoms become covalently bonded to each other through their unfilled orbits. As a result strong covalent bonding between atoms extends throughout the crystals. This accounts for their hardness and high melting points.

5.7.3 Explanation of the Properties of Metals:

Since electrons in metals are free to move from one atom to the next. They are generally good conductors of electricity.

When metal is heated, the mobile electrons absorb heat energy and transfer to neighbouring electrons, this means that metals are good conductors; of heat.

The mobile electrons readily absorb light falling upon them and move to higher energy levels. When they fall back to their original position they emits radiations. This causes the metallic lustre.

 

 
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