Periodic Properties Variation Simulator — Trends Across Groups & Periods

Periodic trends explain why elements behave the way they do based purely on their position in the periodic table, and being able to predict — not just memorize — a trend's direction is one of the highest-leverage skills for AP Chemistry Unit 1 and 3, USNCO, and IChO.

Atomic radius decreases across a period (left to right) because each added proton increases effective nuclear charge on a roughly constant number of shielding inner-shell electrons, pulling the outer electrons in tighter. Atomic radius increases down a group because each successive element adds an entirely new principal energy level, and the increase in shell number outweighs the increase in nuclear charge.

First ionization energy — the energy required to remove the outermost electron from a gaseous atom — generally increases across a period for the same effective-nuclear-charge reason that shrinks radius, and decreases down a group as the outermost electron sits farther from the nucleus and is more shielded. Two systematic exceptions are frequently tested: ionization energy dips slightly from Group 2 to Group 13 (removing an electron from a filled s subshell to a half-empty p subshell is easier than the trend predicts) and from Group 15 to Group 16 (removing an electron from a half-filled p subshell, which has extra stability, to a paired p subshell is easier than expected).

Successive ionization energies within the same atom always increase, but jump dramatically once you cross from valence electrons into core electrons — the enormous jump between an element's nth and (n+1)th ionization energy directly reveals how many valence electrons it has, a classic identification technique.

Electronegativity and electron affinity trends largely parallel ionization energy, both increasing up and to the right toward fluorine, though electron affinity has more numerous and chemically-meaningful exceptions among individual elements.

This periodic properties simulator lets you plot any single trend as a continuous curve across a chosen period or down a chosen group, directly visualizing the increases, decreases, and exceptions that define periodic law — a focused complement to full element-by-element lookup tools.