atomic radius: Within a period, there is a regular decrease in atomic radius with increasing atomic number. Within a group, there is a regular increase in atomic radius with increasing atomic number.

electron affinity: the energy evolved when an atom or ion that gains an electron. Electron affinity increases up and to the right of the periodic table (chlorine has the highest electron affinity).

electronegativity: a ranking of the tendency of an atom to gain an electron. Electronegativity increases up and to the right of the periodic table (fluorine is defined to have the highest electronegativity value: 3.97).

ionization energy: the quantity of energy required to remove a specific electron from an atom, ion, or molecule. Ionization energy decreases within a family (1) with increasing atomic size, (2) with increasing distance between the electron to be removed and the nucleus, (3) with a decrease in number of electrons in the outer shell, (4) with the introduction of a new sublevel, (5) with the addition of an electron to a half-filled sublevel, and (6) with the addition of inner shell electrons that increase repulsion of outer shell electrons.