>> In this video,
we're going to see how
to write electron
configurations just by looking
at the periodic table.
We're going to be able to
read electron configurations
from the periodic table.
So, in order to do that, we
have to know about blocks.
So this is a breakdown
of the periodic table
and we have the s-block,
the p-block,
the d-block, and the f-block.
So the first two columns in the
periodic table are the s-block.
Every element that is in the
first column of the s-block,
its electron configuration
ends in s1.
Hydrogen is 1s1, lithium ends
in 2s1, sodium ends in 3s1,
potassium in 4s1, and so on.
Every element that's in the
second column ends in s2.
Helium ends in -- well, is
1s2, beryllium ends in 2s2,
magnesium ends in
3s2, calcium in 4s2,
strontium in 5s2, and so on.
Everything in the p-block has
its electron configuration
ending in p-something.
If it's in the first
column, it ends in p1,
second column, p2, p3, p4, p5.
And everything in the sixth
column in the p-block,
if that's that element,
its electron configuration
ends in p6.
So neon ends in 2p6, argon
3p6, krypton 4p6, and so on --
p5 for this column, these
are the halogens here --
p4, p3, p2, and p1.
Now, when we're reading the
periodic table, we read it left
to right, top to bottom.
When we finish a row, we go back
down to the beginning
of the next row.
And what this is this is
the same order that you saw
in the last video with
the energy levels.
So it was 1s -- so
these 2 are 1s.
And then we saw 2s right here.
Then we saw 2p come next.
After 2p was 3s.
And then after 3s, we saw 3p.
And after 3p, remember,
we came down to 4s.
And only after we filled
the 4s, could we put 3d.
Now this is the d-block.
And notice that, for the s-block
and the p-block, the row --
the period number is the same
as the sublevel --
2, 3, 4, and so on.
With the d-block, the
sublevel's 1 less --
3d is in the fourth row, 4d is
in the fifth row, and so on.
Now, remember, the f-block
really fits in right here
between 6s-5d, 7s and 6d
and it really goes in here.
So after the 6s, we
come down to the 4f.
After the 7s, we
come down to the 5f.
And the f-block is 2
less than the row number.
So if this is the sixth row, 6
minus 2 is 4 -- we're in the 4f.
Seventh row, we're in the 5f.
So all you have to do to
look at the periodic table
and read an electronic
configuration
for an element is fill in --
read through the periodic table,
filling in the last
column in each block.
So let's say we're down here --
we're in the third
column in the third row
and we're in the p-block.
So we're past the
s-block so we'd say 1s2
because that's helium,
that's the last one.
And then the next
one would be 2s2
and then we're past the
2p-block so it would be 2p6.
That's this one right here.
And we come back here --
it would be 3s2 because
we're past the 3s-block.
And then we're in the
3p-block so it would be 3p3.
So it would look like this.
1s2 -- that gets
us through helium.
2s2 gets us through
here, which is beryllium.
And then 2p6 gets us to the
end of the p-block over here.
Come back.
We pass the 3s-block
so we say 3s2 --
remember, everything
in this column is s2.
And then, we get to the
block that we're in.
We're in the third column
over in the 3p-block.
So we'd say 3p3.
And it ends up that
that's phosphorous.
Now, we can write
the core notation --
noble gas notation --
for this really easily.
All we have to go is to
the previous noble gas.
So, as we're reading this
periodic table from left
to right, top to bottom, if
this is phosphorous right here,
the previous noble gas would
be here, which is neon.
So we could say also
neon -- square brackets.
And then we just have to
do everything after neon,
which would be 3s2, 3p3
-- see how to do that?
So let's do a couple more.
So here's a regular
periodic table.
And let's say we were writing
the electron configuration
for sodium.
Well, there's sodium right here.
So we'd go through
the blocks -- 1s2 --
on this one, helium's over
here but really, it's here.
So 1s2 because we're past there.
Then we're past the
2s-block so 2s2.
And then we're past
the 2p-block, so 2p6.
And then we're in
the first column
of the 3s-block,
so we'd say 3s1.
Or we could just write
noble gas configuration --
the previous noble gas.
So before sodium, the last noble
gas we went through was neon.
So neon and then
just read this 3s1.
So let's say we wanted
to do vanadium.
So same thing.
We would go -- okay,
first the long way.
We're past the 1s-block,
so we'd go 1s2.
We're past the 2s-block,
so we'd say 2s2.
We're past the 2p-block,
so we'd say 2p6.
And we're past the 3s-block, so
we'd say 3s2 -- so we're here.
And we're past the 3p-block,
argon, so we'd say 3p6.
And then we're past
the 4s-block.
We're past calcium because
we're right here, right?
So we'd say 4s2.
And then we are in
the 1, 2, third column
of the 3d-block,
so we'd say 3d3.
Or using core notation,
the previous noble gas was argon
right here, so we'd say argon.
And then just everything
that comes after that
up to our vanadium, so it
would be 4s2, then 3d3.
Easy as that.
So just remember,
read the end of each
of the blocks all the way
through, left to right,
top to bottom until you get
to the block that you're in
and just count over
how many columns.
And then just write the
electron configuration.
Now there are two exceptions
that I'm going to ask you guys
to memorize and just
memorize these, all right?
And these are chromium
and copper.
So chromium, if you just
follow the order of filling,
like we just did, we would
say argon, 4s2, 3d4, right?
But it's not.
Just memorize this.
Chromium is an exception.
Memorize it.
It's argon 4s1, 3d5.
And copper, likewise.
Okay, instead of being 4s2,
3d9 -- 1, 2, 3, 4, 5, 6, 7, 8,
and 9, it's argon 4s1, 3d10.
Basically, the reason for
these is it's just more stable.
It's easier for them to be
like this than the other way.
But pretty much just
memorize these.
So at this point, you
should be able to read off
of the periodic table the
electron configuration
of the ground state
of any neutral atom.
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