| A | B |
|---|
| nucleus | the dense, positively charged mass located in the center of an atom |
| proton | a 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 of an atom |
| 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 from the electrons in an atom |
| orbital | a region of space around a 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 |
