These structures will be used to explain bonding and compound properties in later lessons. The nucleus is very small but it has nearly all the weight of the atom. The nucleus contains protons . Each proton carries a single positive electric charge. The atomic number is the number of protons in the nucleus.
Electrons are outside the nucleus .
Each electron has a single negative electric charge. Electricity is the flow of electrons in wires. This gives atoms an overall charge of zero. Electronic Structure Atoms have shells available for electrons. Electrons fill the innermost shells first.