Ionization energy, or IE, is defined as the
amount of energy required
to strip an atom of one electron.
And yes, ionization can solve mysteries, too.
Tax evasion, counterfeiting, and insurance
fraud-
many of these cases are cracked
by using what scientists know about ionization
energy
that helps identify not only the compound,
but the age of the compounds relative to each
other.
Martha Stewart's insider trading conviction
relied partly on ink source comparisons.
Ionic differences in the ink samplings
suggested key entries were made on separate
occasions
and not in the sequence claimed by the defense.
The ions and chemical energy told a story
that did not match up with Martha's,
and the judge sided with the chemistry,
sending Martha to jail.
(Source: FBI Forensic Science Communications,
July 2005. Vol 7, #3)
Elements that have a high electronegativity
also tend to have high ionization energy.
A high electronegativity suggests
that an element takes electrons in a chemical
reaction
rather than giving them up.
It follows then that it would take high ionization
energy
to remove an electron from an atom with high
electronegativity.
With this fact in mind, can you determine
a periodic trend
for ionization energy?
As we discussed in Section 3, as you move
across a period,
the electronegativity increases,
which means the ionization energy increases.
For example, moving across Period 2,
lithium's ionization energy is 520.2 kilo
joule per mole,
but fluorine's ionization energy
is significantly higher at 1681 kilo joule
per mole.
This supports the periodic trend that ionization
energy increases
as you move across a period.
There is also a periodic trend
that ionization energy decreases as you move
down a group,
which indicates that there is a relationship
between ionization energy
and the atomic radius.
As atomic radius increases, ionization energy
decreases.
Remember too that as electronegativity decreases,
the atomic radius increases.
This is because valence electrons
become easier to remove
when the distance between them and the nucleus
increases.
For instance, moving down through Group 2,
the ionization energy for beryllium is 899.5
kilo joule per mole,
whereas the ionization energy for radium
is lower at 509.3 kilo joule per mole.
