- Matter is anything that has mass and occupies space. It can be classified on the basis of its (i) physical state as solid, liquid or gas, and (ii) chemical composition/constitution as element, compound or mixture.

- An element is basic form of matter that cannot be broken down into simpler substances even by chemical reaction. A compound is a substance composed of two or more different types of elements chemically combined in a definite proportion by mass. A mixture contains more than one substance (element or compound) mixed in any proportion.

- A solution is a homogeneous mixture of two or more than two substances. Major component of the solution is called solvent.

- According to law of constant proportions, a sample of a pure substance always consists of the same elements combined in the same proportions by mass.

- When an element combines with another element and forms more than one compound, then different masses of one element that combine with a fix mass of another element are in ratio of simple whole number or integer. This is the law of Multiple proportions.

-John Dalton introduced the idea of an atom as an indivisible particle of matter. An atom is the smallest particle of an element which can exist and retains all the chemical properties of that element.

-A molecule is the smallest particle of an element or of a compound which can exist freely under ordinary conditions and shows all properties of that substance.