| A | B |
|---|
| atomos | The Greek word for "uncut" |
| thomson | He is responsible for the first evidence of subatomic particles |
| electron | a subatomic particle with the smallest relative mass |
| location | Subatomic particles can be distinguished by mass, charge, and ____. |
| protons | Atoms of different elements have different numbers of _____. |
| isotopes | Atoms of the same element that have different numbers of neutrons. |
| mass number | The sum of protons and neutrons. |
| atomic number | It is equal to the number of protons. |
| energy levels | The possible energies that electrons in an atom can have. |
| energy | An electron in an atom can move from one energy level to another when the atom gains or loses _________. |
| ground state | When all electrons in an atom have the lowest possible energies. |
| electron configuration | The arrangement of electrons in the orbitals of an atom. |
| orbital | The region of space around the nucleus where an electron is likely to be found. |
| electron cloud | A visual model for the likely locations of electrons in an atom. |
| Democritus | The philosopher who first proposed the "atom". |
