Electron affinity is our
next periodic trend.
And we can define electron
affinity as the amount
of energy
associated with
The gain of an electron
by a gaseous atom.
So, this is kind of the reverse
of ionization energy.
Where ionization energy, it's the amount
of energy required to remove the electron,
here it's, I take a particular atom
such as fluorine, and
I'm gonna give it an electron.
Does the fluorine want the electron?
Or does the fluorine
not want the electron?
In this case fluorine has
seven valence electrons.
So, it would really,
really like to have another electron.
The electron affinity associated
with this or the energy associated
with this is negative 328
kilo joules per mole.
And remember that the more negative
the energy the more stable,
so if we have a very
negative electron affinity.
That means that this is
a really good situation.
It's gonna be very, very stable.
So, the higher the negative value,
The higher, The Electron affinity.
And our general trend for
electron affinity, it's gonna decrease
as we go down a group in
the periodic table, and
it's gonna increase as
move across the period.
And again,
I put a little star next to the increase,
because this is not A linear trend.
So, we can analyze this trend again for
the elements in the second
period of the periodic table.
So if we look at our electron affinity,
Versus group number,
We given electron to
lithium it will take one.
Right.
Barillium doesn't want an electron
as much.
So, it's going to drop off.
Boron will continue to increase and
go up with carbon.
With nitrogen it has
a half filled P orbital.
So, we're going to see a dip.
In the stability, when we give
an electron to nitrogen, then oxygen and
fluorine are gonna be pretty high
because they really want an electron.
And remember, each of these
species is trying to achieve an so
it would like to get eight
electrons Since to get eight electrons
we need to take at least one.
So, another thing with
the noble gases here,
is that the noble gases
don't want electrons at all.
So when we typically represent these
they're going to be off the charts in
the opposite direction then they were for
ionization energy.
So, for
electron affinity you need to think of
I have a particular atom,
I'm gonna give it an electron,
will this want to be stabilized or
will it want to be destabilized,
and the higher the negative value,
the higher the electron affinity.
For example, this would be negative
328 kilo joules per mole on the scale.
But we represent that as
the largest affinity, okay?
For neon, the electron affinity is
gonna be much greater than zero.
Because when we give an electron to neon,
it does not want it and
it's gonna become more unstable,
and not become stabilized.
So, these are the general trends that you
need to look at when we discuss electron
affinity.
