Atomic size decreases across a period due to an increase in the effective nuclear charge, zeff.

a. True

b. False

The answer is true. As you move across the periodic table, the elements have a higher atomic charge due to an increase in the number of protons and neutrons. Since the neutrons have no charge, the protons (that have a positive charge) attract the electrons clouds that are negative in charge (unlike poles attract). The more the protons in an atom, the more the attraction on the electron orbits so they get closer to the nucleus of the atoms. This is the reason the atomic diameter reduces across the periodic table.