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of Bonding in Crystal Lattice
exist in two forms, crystalline and amorphous. In the amorphous form,
the solid has definite shape and volume but the arrangement of atoms,
molecules or ions is not regular. In the crystalline form, the solid
has a definite shape and volume and also a regular arrangement of
atoms, molecules or ions in them, thus they have a geometrical shape.
Crystal Structure of Sodium
Sodium crystal is a body-centered cubic crystal. Each sodium ion is
surrounded by eight equidistant sodium ions arranged at the corners of
the cube which is a unit of the crystal. The coordination number of
sodium crystal is eight.
Body-centered cubic structure is less compactly packed, atoms occupy
68% of the total space and as sodium has only one valence electron per
atom, the metallic bond is a weak bond. Thus, sodium is a soft metal.
Crystal of Magnesium
A magnesium crystal is a hexagonal closely
packed crystal with each magnesium ion surrounded by twelve equidistant
magnesium ions. The co-ordination number of magnesium crystal is
Atoms occupy 74% of the total space.
Magnesium has two valence electrons per atom,
hence the metallic bond is stronger than sodium. Thus, it is harder
Crystal of Aluminium
An aluminium crystal is face-centred cubic crystal with each aluminium
ion surrounded by twelve equidistant aluminium
ions. The co-ordination number of aluminium
crystal is twelve.
The open space present in the crystal is 26%.
Aluminium has three valence electrons per
atom. Hence, the metallic bond is stronger than sodium and magnesium.
Thus, aluminium metal is harder than sodium
and magnesium metals.