Periodic Table
Periodic Trends
Three of the four trends point the same way (toward the top right); atomic radius and metallic character are the opposite.
EN and IE increase; atomic radius and metallic character decrease.
Atomic radius and metallic character increase; EN and IE decrease.
Atomic Radius
Across a row, protons increase while electrons fill the same shell, so the stronger nuclear pull draws the electron cloud inward. Down a group, each new period adds a shell, so electrons sit farther from the nucleus.
You will rarely calculate a radius. Instead you rank or compare atoms and ions. Remember cations are smaller than their neutral atom (lost a shell / less repulsion) and anions are larger (added electrons / more repulsion).
Metallic Character
Metallic character tracks how easily an atom gives up electrons. It follows atomic radius: larger, looser atoms (bottom left) lose electrons easily and are the most metallic, while small, tightly held nonmetals (top right) are the least.
Used to predict reactivity of metals and whether an element forms cations. Francium/cesium region is most metallic, fluorine region is least. Metalloids sit along the staircase.
Electronegativity (EN)
EN is an atom's pull on shared bonding electrons. A smaller atom with high nuclear charge (top right, excluding noble gases) holds bonded electrons more tightly, so EN rises toward fluorine, the most electronegative element.
Drives bond polarity and dipoles. Compare EN differences to decide if a bond is nonpolar, polar covalent, or ionic, and to find the partial-negative end of a bond or the most acidic proton.
Ionization Energy (IE)
IE is the energy to remove an electron. Smaller atoms with a strong nuclear pull (top right) hold electrons tightly, so more energy is needed. Larger atoms down a group release their outer electron easily.
Expect large jumps in successive IE once you break into a full (noble-gas) shell, which reveals valence count. Noble gases have the highest IE; alkali metals the lowest.