Protons are found in the nucleus of an atom
Neutrons are found in the nucleus of an atom
Electrons are found outside the nucleus in electron shells or orbitals
To get the number of protons, use the atomic number
To get the number of neutrons, subtract the atomic number from the mass number
To get the number of electrons in a neutral atom, use the same number as the atomic number
To get the number of electrons in an ion, adjust for the charge
Positive charge means fewer electrons than protons
Negative charge means more electrons than protons