We do know that matter is made up of particles which are arranged in a certain way. Gases particles are well separated and can freely move about, solids, on the other hand, have particles that are tightly packed, usually with no scope to move around.
Anything which has mass and occupies space is called matter. It may be solid, liquid or gas.
Matter is of 2 types -
1. Pure Matter
2. Impure substances
Pure substances may be defined as material which contains only one kind of atoms or molecules.
Pure substances are of 2 kinds : -
- Elements -
Pure substances which are made up of only one kind of atoms are known as elements. All atoms in an element are identical. Atoms of different elements are different.
2. Compounds -
Pure substances which are made up of only one kind of molecules are known as compounds. Atoms constituting are from two or more different elements. The different elements are combined in fixed proportion in a compound
Impure matters are also called mixture. A mixture is a material which contains two or more different kinds of particles (atoms or molecules) which do not react chemically but are physically mixed together in any proportion.
Mixtures are of 2 types:
- Homogeneous mixtures -
A mixture is said to be homogeneous if all the components of the mixture are uniformly mixed and there are no boundaries of separation between them. For example- Salt in water etc.
2. Heterogeneous mixtures -
A mixture is sad to be heterogeneous if all the components of the mixture are not thoroughly mixed and there are visible boundaries of separation between them. For example- Sand in water etc.
Physical and chemical changes
- A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour or state of the substance change. No new substance is formed.
- Example: Melting of ice, boiling water.
- A substance is said to undergo a chemical change when a new substance with completely new properties (physical and chemical) is formed.
- Example: Burning of wood or paper, souring of milk.
Solutions and their properties
- A solution is a homogeneous mixture of two or more substances.
- Its particles are too tiny and have a diameter less than 1 nm.
- The particles are not visible to naked eyes.
- Particles do not scatter a beam of light passing through it and hence do not show the Tyndall effect.
- The solute particles never settle down on keeping undisturbed.
- The components of a solution cannot be separated using filtration.
Alloys are homogeneous mixtures of metals or a mixture of a metal and another element that cannot be separated into their components by physical methods.
- Steel, a combination of iron (metal) and carbon (non-metal).
- Bronze, a combination of copper (metal) and tin (metal).
- Brass, a mixture of copper (metal) and zinc (metal).