Classification of matter

Anything that occupies space and has some mass is called as matter. Chemistry is study of matter scientifically, this means that it is a quite wide branch of knowledge .There are 3 states of matter majorly: liquid, gas and solid. A solid is something which has a definite shape and volume. A liquid is something which has a definite volume but takes the shape of its container. 

In order to make sense of tremendous amount of information which we can learn about matter, chemists have developed categories of certain kinds of matter in which to organize the information. If we first examine a thing, and then decide which category it belongs in, we are classifying it. Keep in mind that there are several different systems of categories which are not mutually exclusive. When we classify organisms in biology, we make a decision that a particular animal is male and it is a reptile.

A sample of matter is pure if it has only one identity throughout. A mixture has 2 or more different substances physically blended together so that each retains the identity of its own. Air is a mixture. It contains nitrogen, oxygen, carbon dioxide, and lots of other things, although we can't see them. Virtually everything in the room with you is a mixture. Pepper is a mixture, but salt is a pure state.

An element is a sample of matter which cannot be simplified (note that it is 'simplified' instead of 'purified'). A compound is a sample of matter which can be changed into 2 or more elements. Gold is an element. We can't change gold into anything simpler than gold. Water is a compound. We can change water into hydrogen and oxygen, both of them are simpler forms.