| A | B |
|---|
| Nucleus | The center of an atom; made up of protons and neutrons |
| Proton | A positively charged subatomic particle in the nucleus of an atom |
| Neutron | A neutral subatomic particle in the nucleus of an atom |
| Electron | A tiny negatively charged subatomic particle moving around outside the nucleus of an atom |
| Energy level | Any of the possible energies an electron may have in an atom |
| Orbital | A region in an atom where there is a high probability of finding electrons |
| Valence electron | An electron in the outermost energy level of an atom |
| Atomic number | the number of protons in the nucleus of an atom |
| Isotopes | atoms of the same element with different number of neutrons |
| Atomic mass | number of protons AND neutrons in the nucleus of an atom |
| Metals | elements that are good conductors of heat and electricity |
| Nonmetals | elements that are NOT good conductors of heat and electricity |
| Metalloids | elements that have properties of metals and nonmetals |
| Alkali metals | highly reactive metallic elements of Group 1 |
| Alkaline earth metals | reactive metallic elements of Group 2 |
| Transition metals | metallic elements found in Groups 3-12 |
| Halogens | highly reactive elements located in Group 17 |
| Noble gases | unreactive gases found in Group 18 |
| Ion | atom that has lost or gained an e-, has a net charge |
| Anion | ion with a negative charge |
| Cation | ion with a positive charge |
| Period | horizontal row of elements in the periodic table; shows # of energy levels |
| Group/Family | vertical column of elements in periodic table; shows # of valence electrons |
