Attraction & repulsion of atom:
It can be observed, that if two negatively charged bodies are brought together, there is a force of repulsion between them. Similarly if two positively charged bodies are brought together there is a force of repulsion. However, if a positively charged body is brought close to a negatively charged body, they attract each other. Hence:
Like Charges Repel, Unlike Charges Attract.
The force of attraction or repulsion is governed by an inverse square law
UNIT OF CHARGE
The charge on an electron is very small, therefore a more practical unit of charge called a Coulomb, has been chosen:
One Coulomb = 6.29 x 1018 electrons