All matter is made up by particles that can be protons, neutrons, electrons, atoms, ions ( charged atoms ) and molecules.
These particles are attached to others very tightly ( solids ), not that much ( liquids ) and far appart ( gases ).
ACCORDING TO THE STATE
SOLID
Nota:
Particles in solids are tightly packed. SOLIDS then have DEFINITE volume and shape
LIQUID
Nota:
Particles in liquids are farther appart if compared to SOLIDS, because of this liquids flow and tend to occupy the SHAPE of their container, but keep their volume.
GAS
Nota:
The particles in a gas are far away, they are not attracted among them and move freely.
GASES tend to occupy all available space and this makes them have VARIABLE volume and shape.
ACCORDING TO PROPERTIES
PURE SUBSTANCES
Elements
Nota:
Made up by the SAME kind of atoms.
Compounds
Nota:
Made up by two or more atoms of DIFFERENT elements combined at FIXED ( DEFINITE ) proportions.