Periodic Table Trends
Every periodic trend comes from two ideas: effective nuclear charge pulling electrons in, and added shells pushing them out. Learn the reason and you never have to guess the direction.
Key Facts to Memorize
Atomic radius
Decreases across a period, increases down a group.
Ionization energy
Increases across a period, decreases down a group.
Electronegativity
Increases across a period, decreases down a group. F is highest (4.0).
Electron affinity
Generally becomes more negative (more favorable) toward the upper right.
Metallic character
Opposite of electronegativity: increases down and to the left.
Ionic radius
Cations are smaller than their atoms; anions are larger.
Effective nuclear charge
Increases across a period, which is the engine behind most trends.
Al says…
Fluorine is the champion of almost everything — highest electronegativity, small radius, huge ionization energy. When in doubt, point toward the upper right.
Practice This Topic
External Tools
- Blooket review game
Mrs. Cauthron's periodic-table-trends Blooket set — play it here.
- Ptable interactive periodic table
Toggle the trend overlays to see radius and electronegativity gradients.