After today, you will be able to…
• Explain what ionization energy is
• Describe the ionization energy
trend from the Periodic Table
• Explain why it requires more
energy to remove each subsequent
electron after the first
Unit 4: The Periodic
Trends
Trends with Ionization
Energy (I.E.)
Ionization Energy (I.E.)
• The amount of energy required to
remove an electron from a gaseous atom.
Example: Li  Li+1 + 1e• Depends on:
1.Distance between electron and nucleus
2.Nuclear charge (# of protons)
Group trend: I.E. decreases as you go down
a group due to a greater # of energy levels
Example: Ionization energy for elements in
the same group:
Lithium
vs.
Cesium
e-
More difficult to
remove e- = e- closer to
nucleus = higher I.E.
e-
Easier to remove e- = efurther away from nucleus
= lower I.E.
Period trend: I.E. increases as you
move across a period due to an
increased nuclear charge
Electrons are held more tightly
because of more protons therefore
more I.E. is required to remove an
electron
1st Ionization Energies for
Elements in the First 6 Periods
It always requires more energy to
remove a 2nd or 3rd electron
because they are more attracted
to a positive ion than to a neutral
atom.
1st I.E. - Energy required to remove the
1st electron.
2nd I.E. - Energy required to remove the
2nd electron.
3rd I.E. - Energy required to remove the
3rd electron.
st
1
I.E. <
nd
2
I.E. <
rd
3
I.E.
1st Ionization
Energy
2nd Ionization
Energy
495.9 kJ
4,560 kJ
Magnesium 738.1 kJ
1,450 kJ
Sodium
3rd Ionization
Energy
7,730 kJ
There is a very large increase of
ionization energy whenever an electron
is removed from an atom/ion that is
isoelectronic with a noble gas.
Summary: Ionization Energy
Easy way to remember: THE UPSIDE-DOWN SNOWMAN
Increases
Do now: Complete and
Turn in “Exit Ticket”
Then: Begin WS 3 (Homework)