Core
Periodicity: Ionization Energy & Electron Affinity
Slide 12 of 28
Explanation for the
general trend
The difference in
ionization energy therefore must be due to a difference in the
force of attraction experienced by valence electrons in atoms of different
elements.
Going across, notice three
things:
–one of the charges (the charge
in the nucleus) is increasing
–the number of electrons in the
valence shell is increasing as well, while
–charge
on an electron and the location of the electron being added (the number
of shells) is the same
In other words, both factors
that contribute to and reduce electrostatic force of
attraction changes.
However, since ionization
energy increases, there must be a net increase in force
of attraction going across the period.
In general, between
chemical species (atoms or ions) that contain different numbers
of protons but the same number of shells, the one with the higher
number of protons will have a higher ionization energy.