Periodic Trends 1 Sizes of Atoms Increase from top to bottom on the periodic table Why? There are higher energy levels, and electrons are farther from the nucleus. Atomic Radii Sizes of Atoms Decrease from left to right on the periodic table Why? There are more protons in the nucleus attracting more electrons (electrostatic attraction). Atomic Radii Atomic Radii 4 p. 113 of Chemistry textbook (BJU Press) Question Why do atoms get larger as you go down the periodic table? They are heavier. They are less dense. Electrons are further from the nucleus. Electrons are bigger. 5 (Comparing the size of an atom to that of its ion, not going across or up the table) Sizes of Atoms Ionic Radii Sizes of Atoms Atoms that lose outer electrons have smaller positive ions (metals).