Properties of matter

(a) MOLECULAR PROPERTIES OF MATTER

Molecular properties of matter are based on the behavior of the molecules.

These are observed in the following;

(i) Diffusion

(ii) Molecular forces

(iii) Capillarity

(iv) Surface tension

(v) Elasticity

Molecular forces:

Intermolecular forces are forces of attraction or repulsion between molecules of matter.

The molecules may be of the same substance or of different substance. Types of molecular forces

Cohesion (or Cohesive) force
Cohesion is the force of attraction between molecules of the same kind or same substance.

E.g Forces between water molecules themselves, forces between mercury molecules themselves e.t.c.

Adhesion (or Adhesive) force
Adhesion is the force of attraction between molecules of different kinds or different substances. E.g Forces between water molecules and glass molecules, forces between mercury molecules and glass molecules, forces between water molecules and mercury molecules, e.t.c.

NOTE: The magnitude of the cohesion and adhesion forces determines the:
Shape of liquid meniscus in contact with a solid
Ability of the liquid to wet a substance
Rise or fall in a capillary tube.

When cohesion is greater than adhesion forces, e.g mercury and glass, then the liquid;
(i) Does not wet glass
(ii) Forms spherical balls when spilled on a glass surface
(iii) Depresses in a capillary tube
(iv) Meniscus curves downwards.

image 188

When adhesion is greater than cohesion forces, e.g water and glass, then the liquid;
(i) Wets glass
(ii) Spreads when spilled on a glass surface
(iii) Rises in a capillary tube
(iv) Meniscus curves upwards

image 189

Water spreads on the glass surface due to greater adhesion forces between glass and water molecules than the cohesion forces between water molecules themselves hence wetting the glass.