Does the size of an atom depend on the number of protons it has?
No. The size of an atom does NOT depend on the number of protons it has. It depends on its atomic radius (how big it is). The protons stay in the nucleus, or center of the atom, which takes up about one ten-thousandth of its space. Adding a proton does nothing to increase an atom’s size. For instance, Na (Sodium) is larger than Ar (Argon) even though Argon has more protons. This is because Argon’s positive nucleus is better able to pull in its outer electron shell. There are fewer electrons shielding the outer shell from the effective nuclear charge, so the atom is smaller within a period as the number of protons gets larger.
