| A | B |
|---|
| mass number | the number of neutrons and protons in the nucleus of an atom |
| atomic mass | the total mass of the neutrons and protons in an atom, measured in atomic mass units |
| atomic number | number of protons in the nucleus of an atom |
| atom | smallest part of an element |
| neutron | neutral particle in the nucleus of an atom |
| energy level | place where an electron is most likely to be found |
| proton | positively charged particle in an atom |
| electron | negatively charged particle in an atom |
| isotope | atom of an element with the same number of protons but a different number of neutrons |
| nucleus | small, dense core of an atom |
