Why Everything Around You Is Made of Matter

Matter is anything that occupies space (has volume) and has mass. Every object you see, touch, or use is made of matter, whether it is solid, liquid, or gas. To check if something is matter, see if it takes up space and has weight. For example, a cricket ball, a glass of water, and the air in a balloon all occupy space and have mass, so they are matter. Even invisible air fills a room and can be weighed using a sensitive balance. On the other hand, light and sound are not matter because they do not have mass or occupy space. Many students mistakenly think air is not matter because it cannot be seen, but it meets both conditions of mass and volume.

Molecules are the tiny particles that make up all matter, and they have three main characteristics: they are separated by intermolecular space, are held together by intermolecular force of attraction, and are always moving in a random manner. Intermolecular space is the gap between molecules, which is smallest in solids, larger in liquids, and largest in gases. The intermolecular force is the pull that keeps molecules together; it is strongest in solids and weakest in gases. Molecules are never still—they move continuously and randomly, which is called molecular motion. For example, when you open a bottle of perfume, the scent spreads throughout the room because the molecules move and mix with air. In real life, the sugar you stir into tea dissolves because the sugar molecules move between the water molecules. Some students think molecules in solids do not move at all, but they actually vibrate in place.

Solids, liquids, and gases differ in shape, volume, rigidity, fluidity, and compressibility because of how their molecules are arranged and move. Solids have a definite shape and volume, are rigid, and cannot be compressed easily because their molecules are tightly packed with very little intermolecular space and strong forces of attraction. Liquids have a definite volume but no definite shape; they take the shape of their container, are less rigid, and can flow because their molecules are less tightly packed, with more space and weaker forces than solids. Gases have neither definite shape nor volume, are highly compressible, and flow freely because their molecules are far apart with very weak forces of attraction. For example, ice (solid) keeps its shape, water (liquid) takes the shape of its glass, and steam (gas) fills the whole room. Some students confuse compressibility and fluidity, but only gases are both highly compressible and highly fluid.

A substance changes its state through specific processes, each involving either absorption or release of heat. Melting is when a solid changes to a liquid by absorbing heat, like ice turning into water. Freezing is when a liquid becomes a solid by giving out heat, such as water turning into ice. Vaporisation (boiling) is when a liquid changes to a gas by absorbing heat, like water boiling to become steam. Evaporation is a slower change from liquid to gas at any temperature below boiling, such as wet clothes drying in the sun. Condensation is when a gas turns into a liquid by releasing heat, like water droplets forming on a cold glass. Sublimation is when a solid changes directly to a gas (or vice versa) without becoming liquid, for example, camphor disappearing from a puja plate. A common misconception is that evaporation and boiling are the same, but boiling happens at a fixed temperature while evaporation can happen at any temperature.