Classification of Matter Based on Physical Properties
Matter around us exists in three primary states: solid, liquid, and gas. These states can be identified based on their distinct physical properties. The human body itself showcases matter in all three states — bones and teeth (solids), blood and water (liquids), and air we breathe (gases). Approximately 70% of the human body by weight is water.
While some substances, like wood and stone, only occur as solids, others like camphor, ammonium chloride, and naphthalene can exist in solid and gaseous states. Most substances, such as water and sulfur, can transition between solid, liquid, and gaseous states when conditions like temperature and pressure are altered.
The Solid State
In the solid state:
- Particles are held closely together by strong intermolecular forces.
- The spaces between particles are very small.
- Particles vibrate in fixed positions but do not move from place to place.
General Properties of Solids
Shape and Volume
- Solids have a definite shape and volume.
- Particles in a solid can’t move away from one another, making the shape fixed.
Examples:
- A rubber band returns to its original shape after stretching.
- Salt and sugar have distinct crystal shapes.
- The table you use maintains its shape and occupies a fixed space.
Density
Solids have a high density due to tightly packed particles.
The density of a substance is calculated as:
\[
\text{Density} = \frac{\text{Mass}}{\text{Volume}}
\]
Melting and Boiling Point
- Solids generally have high melting and boiling points, making them solid at room temperature.
Compressibility
- Solids are incompressible because particles are packed closely together.
Exceptions:
- Porous solids (e.g., sponge, loaf of bread) can be compressed as air escapes from their pores.
Flow
- Solids do not flow. Their particles are too rigidly held together to slip past one another.
Expansion or Contraction
- Solids expand very little when heated because particle vibrations only increase slightly.
- Similarly, they contract very little when cooled.
Sublimation
- Certain solids can sublime, or convert directly into vapour when heated, skipping the liquid state.
- Upon cooling, these vapours can revert directly to solid form.
Examples of Sublimation:
- Iodine
- Ammonium chloride
- Camphor
- Naphthalene
- Dry ice (solid CO₂)