Periodic Trends Explorer — Atomic Radius, Ionization Energy & Electronegativity

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Radius shrinks left→right across a period (rising effective nuclear charge) and grows top→bottom down a group (added electron shells).

How it works

Each bar is one element, Z = 1–36 (period 1 through the first transition-metal row). Bar position: column = periodic-table group (1–18), row (depth) = period (1–4). Bar height and color both encode the selected property, normalized 0–1 across the whole set.

All three trends trace back to one idea — the effective nuclear charge Z_eff felt by the outermost electron, approximated by Slater's rules:

Z_eff = Z − S       (S = shielding from inner electrons)
Coulomb pull ∝ Z_eff / r²   (roughly, for the valence electron)

Atomic radius — across a period, each new electron enters the same shell while Z rises faster than shielding, so Z_eff climbs and the shell is pulled in tighter → radius falls. Down a group, a whole new shell (n+1) is added, which outweighs the extra shielding → radius grows.
First ionization energy — the energy to remove the outermost electron scales with how tightly Z_eff holds it, so IE rises across a period (harder to remove, small tight atom) and falls down a group (electron is farther out, more shielded) — almost a mirror image of the radius trend.
Electronegativity (Pauling scale) — the atom's pull on shared bonding electrons; it tracks Z_eff/r the same way, rising across a period and falling down a group. Noble gases (group 18) are left blank — they form essentially no bonds, so the scale doesn't apply to them here.

Highlight period slider dims every bar outside the chosen period so you can read one row's left-to-right trend in isolation; the readout box then averages just that row.

This is the same periodic law Mendeleev spotted in 1869 from chemical behavior alone, decades before anyone knew what an electron shell was — quantum mechanics later explained why the pattern repeats every 2, 8, 8, 18 elements.

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