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.
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
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
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.