| A | B |
|---|
| nucleus | small, dense positively charged center of an atom |
| subatomic particles | protons, neutrons, and electrons |
| proton | subatomic particle that has a positive charge and is found in the nucleus of an atom |
| atomic mass unit | unit used to measure the mass of subatomic particles |
| neutron | subatomic particle with no electric charge that is found in the nucleus of an atom |
| atomic number | number of protons in the nucleus of an atom |
| isotope | atom of an element that has the same number of protons but a different number of neutrons |
| mass number | sum of the protons and neutron in the nucleus of an atom |
| atomic mass | average of teh masses of the existing isotopes of an element |
| electron | negatively charged subatomic particle found outside the nucleus |
| electron could | space in which electrons are likely to be found |
| energy level | most likely location in an electron cloud in which an electron can be found |
| quark | particle that makes up all other know particles in the nucleus of an atom |
| Democritus | named the smallest piece of matter the atom |
