Atomic Bonding in Solids Atomic bonding in solids is the net sum of the

distance-dependent forces or energies: attractive (FA) and repulsive (FR) forces attractive (EA) and repulsive (ER) energies which are.

The net force (FN) or net energy (EN) between two atoms is the sum of both forces or energies; ie. FN = FA + FR EN = EA + ER

The dependence of repulsive, attractive, and net forces /potential energies on interatomic separation for two isolated atoms. ro = Equilibrium Spacing; Eo = Bonding Energy.

When there is no net force (FN = 0) or minimum net energy, a state of equilibrium exists and the centres of the two atoms will remain separated by the equilibrium spacing (r0).

The bonding energy (E0) between two atoms corresponds to the energy at r0, and represents the energy required to separate them.

Many properties of materials depend on E0, curve shape bonding type

In general, Materials with large E0 have high melting point. Solids are formed for large E0, liquids for medium E0

and gases for small E0. Stiffness or elastic modulus of a material is dependent

on the shape of its force vs interatomic separation curve.

The thermal expansion coefficient of a material is related to the shape of its E0 vs r0 curve

Force versus interatomic separation for weakly and strongly bonded atoms.

(a) Plot of potential energy vs interatomic distance, demonstrating the increase in interatomicseparation with rising temperature. With heating, the interatomic separation increases from r0 to r1 to r3 and so on. (b) For a symmetric potential energy versus interatomic distance curve, there is no increase in interatomic separation with rising temperature (ie. r1=r2=r3).

Atomic Bonding in Solids