1. Ionic Radius
Cations are smaller than the atom they originated from because the same number of protons in the nucleus pulls on less electrons
Anions are larger than the atom they originated from because the same number of protons in the nucleus pulls on more electrons

2. Radius of ions increases down a group and decreases across a period
Metals usually become cations
Nonmetals usually form anions

4. Electronegativity
Electronegativity (EN or χ) is the attraction of an atom in a compound for an electron
The scale was developed by Linus Pauling.
EN can be used to determine the type of bond that will form between two atoms.
EN decreases down a group and increases across a period. Group 18 is an exception.