Matter is anything that has mass and occupies space. Everything we see around us is made up of matter—for example, a tennis ball, an apple, and a water bottle. Matter can be described and identified based on its physical and chemical properties. ^[1-4]

Physical properties can be observed or measured without changing the substance itself. These include color, odor, density, melting point, boiling point, conductivity, and solubility. For example, we can observe that a banana is yellow, a rotten egg smells unpleasant, and sugar dissolves in water without altering the substance’s composition.

Chemical properties, on the other hand, describe how a substance interacts with other substances and can only be observed during a chemical change. These include reactivity, such as when iron reacts with oxygen and moisture in the air to form rust. Flammability is another example — coal burns in oxygen to produce carbon dioxide. Acidity can be seen in substances like vinegar, which contains acetic acid, while basicity is a property of substances like baking soda, which is a base.

Because matter exists in many different forms and can have a wide range of properties, scientists have found it useful to classify matter into categories. It helps us better understand, study, and predict how different types of matter behave.

Classification of Matter According to Physical State

States of Matter

One of the simplest ways to classify matter is by its physical state, which refers to its appearance and behavior. The most common states of matter are solid, liquid, gas, and a fourth state known as plasma.

• Solids, such as ice or rock, have a fixed shape and volume. Their particles are tightly packed and only vibrate in place, which keeps the shape rigid.
• Liquids, like water or milk, have a definite volume but no fixed shape. Their particles can move around each other, allowing liquids to flow and take the shape of their container.
• Gases, such as air in the atmosphere or helium in a balloon, have neither a fixed shape nor volume. Their particles are far apart and move freely, spreading out to fill any available space.
• Plasma, often called the fourth state of matter, is made up of extremely energetic, charged particles. It occurs at very high temperatures and can be found in lightning, the Sun, stars, and even neon signs.

Classification of Matter According to Composition

Scientists classify matter not only by its physical state but also by its composition and how it changes, leading to its classification into pure substances and mixtures. ^[1-7]

1. Pure Substances

A pure substance is a matter composed of only one type of material. It possesses the same intrinsic properties (such as boiling point and density) under the same conditions (e.g., temperature and pressure). Pure substances cannot be separated into distinct parts by physical methods, such as filtering or stirring. There are two main types of pure substances: elements and compounds.

i. Elements

An element is the simplest type of pure substance. It is made up of only one type of atom. Elements cannot be broken down into anything simpler. There are 118 known elements in the Periodic Table.

Examples

Gold (Au), oxygen (O₂), iron (Fe), and hydrogen (H₂) are all different elements. Some elements, like gold and silver, are metals, while others, like oxygen and nitrogen, are gases.

ii. Compounds

A compound is a pure substance formed when two or more elements combine chemically. In a compound, the constituent elements lose their individual properties and form a new substance with distinct chemical and physical properties.

Examples

Water (H₂O) is a compound formed from hydrogen and oxygen, yet it has entirely different properties from either of the gases it is made from. Similarly, table salt (NaCl) results from the combination of sodium, a highly reactive metal, and chlorine, a toxic gas—but together they form a stable, edible compound that is essential for human health.

Pure substances are important in science and everyday life. Elements like oxygen help us breathe, and compounds like water are essential for survival.

2. Mixtures

A mixture consists of two or more substances that are combined but not chemically bonded. It indicates that each substance in the mixture retains its properties, allowing the components to be separated physically. There are two main types of mixtures: homogeneous mixtures and heterogeneous mixtures.

i. Homogeneous Mixture

A homogeneous mixture is one where the substances are evenly spread out, and you cannot see the different parts. It looks the same all the way through. 

Examples

Saltwater is a homogeneous mixture because the salt dissolves completely in the water. Similarly, vinegar is a uniform solution of acetic acid in water. Air is another example—a homogeneous mixture of different gases.

ii. Heterogeneous Mixture

A heterogeneous mixture is a mixture where the substances are not evenly spread out, and you can see the different parts.

Examples

A bowl of salad, where you can see the lettuce, tomatoes, and cucumbers separately. When sand and water are mixed, the sand settles at the bottom instead of dissolving. Other examples include trail mix, oil and water, and a bowl of cereal with milk.