An atom is small particle of  molecule which parts in reaction directly. It contains electron, proton and neutron.it is structural and functional unit of  a matter.as for example that any atom contain 20 proton is  Calcium Ca. A human hair is equal to about a million carbon atom across.

characters of  atom :

1. No create  or  destroy of  atom 

2. unique of  element 

3. basic part  of  element 

4. having proton, electron and neutron around the nucleus.

5. It can be   negative or  positive.

6. Molecule is built with consist of atoms.