Periodic Table Trends
How atomic properties change across periods and down groups. Electronegativity, atomic radius, ionization energy, and electron affinity follow predictable patterns that explain chemical reactivity.
Electronegativity
Low
High
Electronegativity
Low
High
This diagram incorrectly shows electronegativity increasing downward. Larger atoms have their valence electrons farther from the nucleus, reducing the effective nuclear charge felt by bonding electrons and lowering electronegativity.
Electronegativity increases from left to right across a period (increasing nuclear charge) and from bottom to top within a group (smaller atomic radius). Fluorine in the upper right is the most electronegative element at 3.98 on the Pauling scale.
Atomic Radius
Small
Large
Atomic Radius
Small
Large
This diagram reverses the trend by showing radius increasing upward and to the right. Adding protons without adding new shells pulls electrons inward, so atoms get smaller across a period from left to right.
Atomic radius increases going down a group (more electron shells) and decreases going left to right across a period (increasing nuclear charge pulls electrons closer). Cesium and francium have the largest atomic radii among naturally occurring elements.
Ionization Energy
Low
High
Ionization Energy
Low
High
This diagram incorrectly shows ionization energy increasing downward and to the left. Larger atoms hold their outermost electrons more loosely because of increased shielding and greater distance from the nucleus.
First ionization energy increases from left to right (stronger nuclear attraction) and from bottom to top (valence electrons closer to the nucleus). Noble gases and halogens have the highest ionization energies in each period.
Electron Affinity
Low
High
Electron Affinity
Low
High
This diagram incorrectly shows electron affinity increasing toward the lower left. Elements in the lower left are metals that tend to lose electrons rather than gain them, giving them low or even positive (endothermic) electron affinities.
Electron affinity generally becomes more exothermic (more negative) toward the upper right of the periodic table. Halogens have the highest electron affinities because adding one electron completes their valence shell. Chlorine has the most exothermic electron affinity at -349 kJ/mol.