The first thing we need to do to find electron
configurations is to find the number of electrons
for the element. So we can find this the periodic
table. And we're going to look at the number
above the element symbol, which is called
the Atomic Number. That will tell us the number
of protons, but it will also tell us the number
of electrons. And we can use that number as
we try to find the electron configuration
for whatever element we're interested in.
So we'll try an example with Boron. You can
see we have this chart here, and this is the
general format you'll see them in. We have
Boron, we know we have five electrons. So
we'll follow the chart and we'll go down,
with the 1s, so we write 1s. And we know that
1s holds up to two valence electrons. Then
we have the 2s, following the arrow down there,
that holds two electrons as well since it's
a s orbital. We've used 4 electrons. Remember
we have five for Boron.
Then we go down this row here with the 2p
and the 3s. We only need one more electron
to get five. We know that the p holds up to
6, but we only need one. So that's our configuration
for Boron. 1s2 2s2 2p1. Notice that the numbers
add up to five, just like the number of electrons
for the element.
Let's try another one - Chlorine. So for Chlorine
we have an atomic number of 17. 17 protons,
but importantly for us, 17 electrons. So we'll
go down, we have the 1s, and that holds two,
we then have the two s, that holds two since
it's an s orbital, and then we'll go down,
2p, which holds up to six, and we'll put six
in there. If you add those number up we've
used ten electrons so far, we have 17. And
after the 2p in that row we have 3s which
holds two, we've used 12 electrons now. And
then we'll go down this row here where we
have the 3p and p holds up to six but since
we have 12 we only need five more to get 17.
That's the electron configuration for Chlorine.
Let's do one more. Vanadium has 23 electrons.
Again, we have the 1s which has two, we have
the 2s which holds two, then we go to the
2p with six, we've used ten, then we have
the 3s, which holds two, and then we go down
the 3p and 4s, and then we've used 20 electrons,
so we need three more and we have the 3d so
we'll just put those last three in the 3d
orbital. That's the electron configuration
for Vanadium. Really important though, we
have 4s2 and then we go down to 3d, and that's
something that you should be aware of, it
is supposed to do that, that's not an error.
Remember that when were doing electron configurations
we're just putting electrons around the nucleus
in the pattern that we find them in nature.
That's all. We can use this information to
predict how atoms form chemical bonds and
how they behave. So it's very useful to help
us understand chemical bonding.
So these are some electron configurations,
the way to get really good at this is practice.
Try a problem, then check your answer, then
try another, and do that until you can get
them right without any problem.
This is Dr. B with how to do electron configurations
and thanks for watching.
