Solid state:Typical properties, Types of Solids, melting and freezing point and Sublimation

Solid state:Typical properties

Unlike liquids the particles in solids are not free to move in solid particles are closely the packed together and have fixed position. They can only vibrate about their mean positions. solids are therefor incompressible and do not flow.

Melting and freezing point

The temperature at which solid turns into liquid is known ad melting point.

The temperature at which liquid changes into solid is called freezing point.

Explanation

When solid is heated, the particles of solid vibrate about their mean positions more rapidly.. At certain temperature, vibration of particles become so effective that particles start leaving their fixed positions. The arrangement of particles In solid breaks down and solid starts melting.

On the other hand, on cooling, movement of liquid molecules becomes slowly and slowly. At certain temperature, liquid sart freezing. Thus, freezing is reverse of melting of solids.

Sublimation

The process in which, a soloid is directly converted into vapours on heating sand vapours are directly converted into solid on cooling without passing through liquid state is called sublimation.

For example, substances like, iodine, benzoic acid, ammonium chloride etc show sublimation.

Types of Solids

There are two main types of Solids depending upon their macroscopic appearance. The appearance is based on the arrangement of particles In solid.

I. Crystalline solid: A crystall solid is a solid that is composed of orderly repeting three dimensional arrangement of particle. This means a crystalline solid has;

I. Well defined shape due to orderly arrangement of particles

Ii. Sharp melting point

Amorphous solid

An amorphous solid is the solid that lacks ordered arrangement of particles. This means amorphous solids:

I. don't have well defined shape due to lack of orderly arrangement of particles.

II. don't have shape melting point but gradually soften on heating.

Allotrops

The different forms of an element in the same physical state and phase are called allotropic form are allotropes.

Example 1

There are three allotropic forms of carbon: diamond, graphite and bucky ball.

In these allotropic forms, arrangement of carbon atoms are different. For example, in diamond, each carbon atom is nbonded to four carbon atoms in three dimensional array. This compact arrangement makes diamond hardest substance.

In graphite, each carbon atom is bonded to three carbon atoms in layer of hexagonal array. Weak bonds exist between the layers which can allow to slide these layers one on another. This makes graphite soft

In bucky ball 60 carbon atoms form a hollow sphere.

Example 2

Another example is a non metal Phosphorus. It is found in two allotropic forms:white Phosphorus and red Phosphorus.

White phosphorus consists of tetra atomic molecules (P4). These molecules are not bonded to each other.

Red phosphorus consists of P4 molecules bonded to one an other in long chains.

Example 3

Sulphur consists of molecules of eight S atoms, S8. Sulphur also exists in several crystalline and amorphous forms. Rhombus and monoclinic forms are its important crystalline allotropes. Plastic Sulphur is the amorphous form

Comparison of physical state of matter.

Question: How can we depreciate between different states of matter?

We can differentiate three States of matter with regards to intermarcular forces private between their particle.

For a gas, there are no attractive forces between the molecules. So gas molecules move freely in all directions. A gas has no definit shape and volume.

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