| Angular momentum quantum number | (also known as the azimuthal quantum number.) The quantum number that distinguishes orbitals of given n having different shapes; it can have any integer value from 0 to n - 1. |
| Atomic number (Z) | the number of protons in the nucleus. |
| Atomic orbital | a wave function for an electron in an atom; pictured qualitatively by describing the region of space where there is a high probability of finding the electron. |
| Electron | a very light particle that carries a unit negative charge and exists in the region around the positively charge nucleus. |
| Electron affinity | the energy change for the process of adding an electron to a neutral atom in the gaseous state to form a negative ion |
| Electron configuration | the particular distribution of electrons among available subshells |
| Group (of the periodic table) | the elements in any one column of the periodic table |
| Ionization energy | the energy needed to remove an electron from an atom (or molecule) |
| Magnetic quantum number (ml) | the quantum number that distinguishes orbitals of given n and 1-that is, of given energy and shape-but having a different orientation in space; the allowed values are the integers from -1 to +1 |
| Metal | a substance or mixture that has a characteristic luster, or shine, is generally a good conductor of heat and electricity, and is malleable and ductile. |
| Nonmetal | an element that does not exhibit the characteristics of a metal |
| Period (of the periodic table) | the elements in any one horizontal row of the periodic table |
| Periodic law | a law stating that when the elements are arranged by atomic number, their physical and chemical properties vary periodically |
| Periodic table | a tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements |
| Principal quantum number (n) | the quantum number on which the energy of an electron in an atom principally depends; it can have any positive value: 1, 2, 3, etc. |
| Spin quantum number (m,) | the quantum number that refers to the two possible orientations of the spin axis of an electron; possible values are +1/2 and -1/2 |