Ionization Energy - across a Period and down a Group TRENDS

Ionization Energy - across a Period and
down a Group
TRENDS FOR IE 1
Group 0 elements (noble gases) have the
highest ionisation energies: helium has the
highest and the value decreases as it goes
down the group. Noble Gases are very stable,
thus electrons are held very tightly and are
harder to remove.
Group 1 elements (excluding hydrogen) have
the lowest ionisation energies for the first
electron removed.
Be is higher than Li in Ionisation 3 than in ionisation 2
The next element in line will be have the highest ionisation energy as it goes down. For
example, in ionisation 1 the highest will be He, then in ionisation 2 will be Li, then Be and
so on.
REASONS
Across the period (horizontal) -> Increasing:
The general trend is for ionisation energies to increase across a period.
In period 2, all outer electrons are in the same level of orbital as the elements all have 2
electron shells. Therefore, electrons are all of the same sort of distances from the
nucleus.
However, the major difference is the increasing number of protons in the nucleus as you
go across the period, from lithium to neon. This causes greater attraction between the
nucleus and the electrons and so the ionisation energies increase.
As the nuclear charge increases (nuclear charge numerically equal to atomic number), the
attraction between the nucleus and the electrons increases and it requires more energy to
remove the outermost electron and that means there is a higher ionisation energy. Down the groups (vertical) -> Decreasing:
Elements down the groups have increasing number of valence shells. Hence, distances of
electrons from the nucleus increase and this account for less pull exerted on the electrons.
As such, IE decreases down the groups. As subsequent electrons are removed:
Trend: Group 2 elements have the lowest IE for the second electron removed
As subsequent electrons are removed the IE increases for each element. When removing
an electron from a new shell (e.g. 2nd electron of element with 1 valence electron), the IE
shows a significant increase.