What are some common mistakes students make with periodic trends?
One of the most common mistakes made by students is the periodic trend of atomic size.
As you go across a period, the atoms actually become smaller. You might think that because you add protons, electrons, and neutrons, the atom would get bigger. Not so!! The increased number of protons (increased effective nuclear charge) pulls even more on the oppositely charge negative electrons surrounding the nucleus. Thus within a period, the atoms become smaller as you go from left to right within the same period.