Trends in Physical Properties

Concept First: Why Size, Energy, and Attraction Matter

The periodic table is not just a list of elements; it is a map of how atoms behave. The physical properties of elements — their size, the energy needed to remove an electron, the energy released when an electron is added, and their ability to attract electrons in a bond — all change in a regular, predictable way as you move across a period or down a group. These trends are not random. They are the direct consequence of two competing forces: the pull of the nucleus on the electrons, and the shielding effect of inner electrons that weakens that pull. …