1. APPENDIX E
Atomic radii represent the sizes of isolated, electrically-neutral atoms, unaffected
by bonding. The general trend is that atomic sizes increase as one moves down a
group. This is due to additional energy levels produced as electrons are added.
Atomic radii decrease, however, as one moves from left to right, across the
Periodic Table. Although more electrons are being added to atoms, they are at
similar distances to the nucleus; and the increasing nuclear charge "pulls" the
electron clouds inwards, making the atomic radii smaller.
Below is a diagram showing the relative size of atoms. The atoms sizes are in
picometers (pm = 10-12 m). Please notice that the d and f blocks are not present.