Across a period (left to right)
- Atomic radius decreases — increasing nuclear charge pulls electrons closer
- Ionization energy increases — harder to remove an electron
- Electronegativity increases — greater pull on shared electrons
- Metallic character decreases
Down a group (top to bottom)
- Atomic radius increases — additional electron shells
- Ionization energy decreases — outer electrons are farther from the nucleus
- Electronegativity decreases
- Metallic character increases
Memory hook
Think of ionization energy and electronegativity as moving together, and atomic radius as moving opposite to both. If you remember the radius trend and one other trend, you can derive the rest.
Common exam trap
Noble gases are often left out of electronegativity comparisons since they don't typically form bonds — don't include them when asked to "rank the electronegativity of these elements" unless the question specifically includes one.