Periodic Trends and Table Structure

Atomic radius changes predictably across the periodic table, and once you get the pattern, it's dead easy to remember. As you move across a period (left to right), atoms get smaller because there are more protons pulling the electrons closer to the nucleus. Moving down a group makes atoms bigger since you're adding more electron shells.

Ionisation energy follows the opposite trend to atomic radius. It increases across a period because those extra protons make it harder to remove an electron. Going down a group, ionisation energy decreases since the outer electrons are further from the nucleus and easier to remove.

The periodic table is cleverly divided into blocks based on electron configuration. The s-block $groups 1-2$ has valence electrons in s orbitals, whilst the p-block $groups 13-18$ has partially filled p sub-shells. Transition metals form the d-block with partially filled d sub-shells, and the bottom rows contain the f-block elements - the lanthanides and actinides.

Quick tip: Remember that trends in atomic radius and ionisation energy are opposites - when one increases, the other decreases!