Protons- determine the identity of an element, they have a positive charge, located in the nucleus, cannot change the amount in an element without changing the element. Atomic Number- the number of protons in the nucleus of an element. The number of electrons in neutral element. Neutron- they do not have a charge, they are located in the nucleus, can change the amount. Isotopes- atoms that have the same number of proton but a different number of neutrons Atomic Mass- protons plus neutrons Average atomic mass- the weighted average of the atomic mass. Electron- negatively charged particle, orbits nucleus, responsible for how the atom bonds Ions- when an atom has more or less electrons than neutral state leaving the atom with a positive or negative charge. Nucleus- central core of an atom containing protons and neutrons.