| A | B |
|---|
| nucleus | a 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 |
| neutron | a neutral subatomic particle that is found in the nucleus of an atom |
| atomic number | equals the number of protons in an atom of that element |
| mass number | the sum of the protons and neutrons in the nucleus of that atom |
| isotopes | atoms of the same 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 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 | when all the electrons in an atom have the lowest possible energies |
