The nucleus contains postitively charged protons and neutral neutrons . Here's periodic table of the elements. Nuclei with the same number of protons but different numbers of neutrons are called isotopes. Many elements have several common isotopes. The charge of the proton is equal and opposite to the charge of the electron.
Neutral atoms have equal numbers of electrons and protons, and thus have no net electrical charge.
This is the form of matter most familar to us. But when heated or exposed to radiation, atoms can lose electrons and become ions, which are atoms with an imbalance between electrons and protons, i.e. they are electrically charged. The process by which an atom loses electrons is called ionization . The number of electrons stripped off is called the state of ionization . In astronomy, we use a special terminology to indicate various states of ionization.