atomic radii and ionization

[malcolm]

what is the effect of ionization on atomic radii? i assume that an anion has a larger radius than a neutral atom and that a cation has a smaller radius. this would mean that the attractive force between the protons and electrons would increase when there are less electrons and decrease when their are more.

or does changing the balance in either way mean that the attraction is greater, regardless of whether there is increase in positive or negative charge, and thus that either type of ionization decreases atomic radius?

[silkworm]

Ionization (in terms of making an anion) is more difficult as atomic size decreases. Study effective nuclear charge (symbolized Zeff) for more clarity.

[jowrose]

Zeff can be crudely designated as the number of electrons in an atom minus the number of "core" electrons (aka all electrons except the valence ones). When using this calculation, it can be seen that Zeff (written as Z subscript "eff") increases along a period (not taking into acount transition metals). This means that atomic radius decreases along a period, and also makes the ionization energy (and electronegativity) a lot higher. However, there are some exceptions. Take O and N, for example. The I.E. of O is smaller than that of N because with N you are removing an electron from a half-filled p subshell, which is somewhat stable.