The existence of negative and positive charges on these materials can be explained on the basis of the structure of the atom. Almost all the mass of an atom resides in a central nucleus which contains a number of tightly packed protons and neutrons. As the protons are positively charged particles, the nucleus has a positive charge. Around the nucleus orbit the same number of electrons having negative charge. These electrons orbit round the nucleus in specific orbits at different distances from the nucleus. As the number of protons and electrons in an atom is the same, the atom as a whole is electrically neutral.
