✔ 最佳答案
Why we cannot use the effective nuclear charge to explain that ionization enthalpy?
It is because we are unable to compare the effect of nuclear charge of two elments which are in different periods (O in 2nd period, S in 3rd period). Therefore,we can only use effective nuclear charge to explain those in the same period. For instance, O and C are in the 2rd period, so the significant factor affecting their ionization enthalpies is the effective nuclear charge and shielding effect(you should know the charge effect is significant than that of sheilding).
Yes, you are right. We know that the more protons, the greater the effective nuclear charge(greater attraction). But we also know that longer distance between the outermost shell electrons and the nuclus, the weaker the attraction among them. Across the period and the group, we cannot predict whether the increase in charge or the decrease in attraction has greater effect on the ionization enthalpy.
No, you are wrong. The effective nuclear charge is extremely related to the atomic radius. Across the period, the increasing in effective nuclear charge causes greater attraction to the outermost shell electrons, so the atomic radius decrease in a given period.Across a group, the outermost shell electrons are further away from the nuclus, so weaker attraction, so the atomic radius increase down a group.
As what I have mentioned above, the increase in atomic radius reduse the attraction of outermost shell electrons from nuclus, so the ionization enthalpy of the atom with larger atomic radius will become lower.
2008-11-03 18:48:20 補充：
1.We can predict the IE in term of effective nuclear charge arcoss a period!
2008-11-03 18:48:26 補充：
2.The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. The term effective is used because the shielding effect of negative electrons prevents higher orbital electrons from experiencing the full nuclear charge.
