| A | B |
|---|
| Nucleus | a dense, positively charged mass located in the center of the atom |
| Proton | positively charged subatomic particle that is found in the nucleus of an atom |
| Electron | a negatively charged subatomic particle that is found in the space outside the nucleus |
| Neutron | a neutral subatomic particle that is found in the nucleus of an atom |
| Atomic Number | a unique number for each element that equals the number of protons in an atom of that element |
| Mass Number | the sum of the number of protons and neutrons in the nucleus of an atom |
| Isotopes | atoms of a given element that have different numbers of neutrons and different mass numbers |
| Energy Levels | the possible energies that electrons in an atom can have |
| Electron Cloud | a visual model of the most likely locations for the electrons in an atom |
| Orbital | a region of space around the nucleus where an electron is likely to be found |
| Electron Configuration | the arrangement of electrons in the orbitals of an atom |
| Ground State | a state in which all the electrons in an atom have the lowest possible energies |
