All materials are made from atoms. The atom of any element consists of small positively charged particles at the center of which is the nucleus, surrounded by a cloud of negatively charged particles called electrons. The nucleus is composed of positive charge protons and neutral charge neutrons. In the normal atom, the number of protons in the nucleus is equal to the number of electrons.

The charge of a proton is equal to the charge of the electron in magnitude, but it is positive:

q _e = 1.6 x 10 ^-19 Coulomb (C)