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· Nuclear charge the more protons (+ charge) in the nucleus, the more strongly the electrons(
charge) are attracted to it
· Electron shielding the more inner shells there are, the weaker the attraction to the nucleus
Across periods 2 and 3
Generally IE increases due to more protons, greater nuclear charge.
Group 2 and 3 (B and Be, Mg and Al too but in 3s and 3p)
B outer electron is in a 2p orbital instead of an 2s orbital (which Be's is in). Electrons in a 2p
orbital are found further from the nucleus. Increased distance results in reduced attraction. B also
has more electron shielding.
Group 5 and 6 (N and O, P and S)
Same shielding, electron removed from same orbital. O and S have a 2px2 pair of electrons where N
and P only have one electron in the 2pxorbital. The repulsion between the two electrons in O
and S makes an electrons easier to remove.
Down a group
IE decreases. The effect of the extra protons is compensated for by the effect of the extra