Every atom has proton, neutron and electron. Proton has positive charge, electron has negative charge and neutrons have no charge. In every stable atoms, number of electrons and protons are same. So every stable atoms have zero electrical charge.
Lets take an example of sodium atom which has 11 protons and 11 electrons so it is electrically stable means there is no charge on sodium atom. But know that sodium has 1 free electron in its outer layer and if we remove this electron than sodium atom will have positive charge.