| A | B |
|---|
| Electromagnetic force | Force of attraction or repulsion between particles of an atom. |
| Energy level | Most likely location in an electron cloud in which an electron may be found. |
| Nucleus | Small, dense positively charged center of an atom. |
| Mass Number | Sum of the protons and the neutrons in the atom. |
| Atomic Mass | Average of the masses of the existing isotopes of an element. |
| Proton, neutron, or an electron | Subatomic particle |
| Neutron | Subatomic particle with no charge located in the nucleus of an atom. |
| Atomic Mass Unit | Unit used to measure the mass of subatomic particles. |
| Strong force | Force that binds protons and neutrons in the nucleus. |
| Gravity | The weakest force, depends upon the mass of the two objects and the distance between them. |
| Electron Cloud | Space in which electrons are likely to be found. |
| Weak force | Force that is the key to the power of the sun; responsible for the process of radioactive decay. |
| Quark | Particle that makes up all the other known particles in the nucleus of the atom. |
| Proton | Positively charged subatomic particle located in the nucleus of the atom. |
| Isotope | Atom that has the same number of protons as another atom (of the same element), but a different number of neutrons. |
| Atomic Number | Number of protons in the nucleus of an atom. |
| Electron | Negatively charged subatomic particle found in an area outside the nucleus of an atom. |
