States and Properties of Matter

Anything that has mass and occupies space is called matter.

According to physical state, matter is commonly classified into three types

Solid

Liquid

Gas

📚 These different physical states arise mainly because of differences in particle motion, intermolecular attraction and the spaces between particles.

👉 Solid: Under ordinary conditions of temperature and pressure, a substance that has a definite shape and a definite volume is called a solid.

Examples: gold, silver, copper, stone, wood, sand, salt, etc.

📚 In a solid:

⭐ The particles have relatively low kinetic energy.

⭐ The intermolecular force of attraction is comparatively strong.

⭐ The intermolecular spaces are very small.

Properties of Solids:

⭐ At a given temperature and pressure, a solid generally has a definite shape and a definite volume.

⭐ Under ordinary conditions, its shape and volume do not change appreciably unless an external force is applied.

⭐ Even under high pressure, the volume of a solid decreases only very slightly. Therefore, solids are almost incompressible.

⭐ At ordinary temperature, solids do not spread out like gases and do not flow like liquids.

Exception: Some solids such as iodine, camphor and naphthalene can change directly into vapour on heating or even gradually under suitable conditions. This process is called sublimation.

⭐ Many solids are crystalline and have an ordered structure; for example: ice, copper sulphate crystals, common salt and alum.

Some solids are amorphous or do not have a regular crystalline shape under ordinary conditions; for example: glass and pitch.

👉 Liquid: Under ordinary conditions, a substance that has a definite volume but no definite shape is called a liquid.

Examples: water, milk, mercury, alcohol, etc.

📚 In a liquid:

⭐ The kinetic energy of particles is generally greater than in solids but lower than in gases.

⭐ The intermolecular force of attraction is weaker than in solids but stronger than in gases.

⭐ The intermolecular spaces are greater than in solids but smaller than in gases.

Properties of Liquids:

⭐ At a given temperature and pressure, a liquid has a definite volume but no definite shape. It takes the shape of the container into which it is poured.

⭐ The volume of a liquid decreases only slightly even when high pressure is applied, so liquids are only slightly compressible.

⭐ Most liquids expand when heated.

⭐ Evaporation can take place continuously from the surface of a liquid at ordinary temperatures.

⭐ When a liquid is at rest in a container, its free surface is generally horizontal.

⭐ Liquids can flow from one place to another and can be poured.

👉 Gas: Under ordinary conditions, a substance that has neither a definite shape nor a definite volume is called a gas.

Examples: air, oxygen, nitrogen, hydrogen, etc.

📚 In a gas:

⭐ The particles generally have the highest kinetic energy among the three common states.

⭐ The intermolecular force of attraction is very weak.

⭐ The intermolecular spaces are very large.

Properties of Gases:

⭐ A gas has neither a definite shape nor a definite volume. Many gases are colourless and therefore cannot be seen directly.

⭐ Even a small quantity of gas spreads out to occupy the available space in its container.

⭐ A gas must be kept in a closed container; otherwise, it spreads into the surrounding space.

⭐ Different gases can mix with one another in any proportion if they do not react chemically.

⭐ The density of a gas depends strongly on its temperature and pressure.

⭐ At the same temperature and pressure, equal volumes of gases contain equal numbers of molecules. This is known as Avogadro's law.

Similarities among Solids, Liquids and Gases:

🔹 Matter in all three states generally expands when heated and contracts when cooled, although the amount of expansion is different for each state.

🔹 If no matter is added or removed, the mass of a substance remains the same when its physical state changes.

🔹 The density of most substances changes with temperature.

🔹 Matter in all three states occupies space.