The periodic table is not just a list of elements -- it reveals powerful patterns in atomic properties. These trends are driven by changes in atomic structure as you move across periods and down groups.
Atomic radius increases going down a group because each row adds a new electron shell, making the atom larger. It decreases going across a period (left to right) because more protons pull the electron cloud inward.
Ionization energy is the energy required to remove an electron from a neutral atom. It increases across a period (electrons are held more tightly) and decreases down a group (outer electrons are farther from the nucleus and easier to remove).
Electronegativity measures an atom's ability to attract bonding electrons. It follows the same trend as ionization energy: increases across a period and decreases down a group. Fluorine is the most electronegative element.
Electron affinity is the energy change when an atom gains an electron. Halogens (Group 17) have the most negative electron affinities because they are one electron short of a full shell.
All periodic trends can be explained by Coulomb's law, which describes the force between charged particles:
As the nuclear charge (\(q_1\)) increases across a period, the attractive force on electrons grows stronger. As the distance (\(r\)) increases down a group, the force weakens. This single equation explains every major periodic trend.