In this video, we are going to write
out the electron configuration and
draw the orbital block diagrams for
the first 18 elements.
And we are gonna be drawing the ground
state electron configurations and
remember that for
an atom in its ground state,
the number of protons is gonna
equal the number of electrons.
So I have listed here,
the atomic numbers and the elements for
the first 18 listed in
the periodic table and
the electron configuration and
the orbital block diagram
have to contain the number of
electrons in each atom which,
like I said, for
an atom will equal its atomic number.
So when these configurations
are put together,
we have to get the lowest
energy configuration possible.
So for hydrogen, which has 1 electron,
it's gonna have an electron configuration
of 1s1 and we need to put 1 electron
in that orbital diagram and
by convention we typically represent
the first electron as spin up.
When we look at helium now, there are
gonna be 2 electrons, so they are gonna
go in the 1s orbital because remember
each orbital can hold 2 electrons, okay?
So the first electron is gonna
go spin up in the 1s orbital and
to minimize propulsion the second
one is gonna go in spin down.
When we go to lithium we're gonna
completely fill up the 1s orbital with 2
electrons and
then next in energy is the 2s orbital,
and we're gonna put 1
electron in that orbital.
So when we draw the orbital block diagram,
in addition to filling up the 1s orbital,
we also put an electron in the 2s orbital.
For beryllium,
our electron configuration is
gonna be 1s22s2 for
a total of 4 electrons.
So the orbital diagram then would have
two electrons in each of the 1s and
the 2s orbitals.
And one's gonna be spin up and one's gonna
be spin down in each of those orbitals.
For boron we need to fit
5 electrons in there, so
we will fill up the 1s2 and
the 2s2 orbitals and
in addition, we have to put
an electron in the 2p orbital.
So we have to fill in we go one,
two three,
four, five electrons in
this orbital diagram.
For element number 6 which is carbon,
we need to use 6 electron,
so that's gonna be 1s2,
2s2, 2p2, for a total of 6 electrons.
The first two orbitals, the 1s and
the 2s, are gonna be filled just like
they were for the other elements, but now
we have to make sure we follow Hund's Rule
which says that we put one electron
spin up in one of the two P orbitals,
and another electron spin in
that second P orbital, okay?
So the electrons are not gonna
pair together unless they have to,
we'll get to that example in a second.
So now for
nitrogen which has 7 electrons we do 1s2,
2s2, 2p3, so
we fill in the 1s and the 2s
orbitals just like we did before and
then we need three electrons in the p
orbitals which are all gonna go
spin up and
that again follows Hund's Rule.
For oxygen, we'll do 1s2 2s2 2p4, for
a total of 8 electrons, so we fill
in the 1s and the 2s just as before.
Then we have to put four electrons in this
p orbital, so we go one, two, three, four.
So now we fill up all
the electrons spin up, and
we have to put one electron spinning down,
in that p orbital for oxygen.
For fluorine, our electron configuration
has to contain 9 electrons,
so it's gonna be 1s2, 2s2, 2p5.
So, we go, one two three, four,
five, six, seven, eight, nine, for
the nine electrons here in the fluorine.
For neon, which is our noble gas,
we go 10 electrons,
or 1s2, 2s2, 2p6, so we have to
fill up the 1s and the 2s orbital.
And now we need six electrons
in this p block, so
we go one, two, three, four, five, six.
And notice when we fill up that p orbital,
each of the individual p orbitals,
the Px, the Py, and the Pz,
each contain two electrons for
a total of six in that P orbital, okay?
And once we fill up those orbital's
every time we add an extra electron it
will go in to the orbital
of the next highest energy.
So for sodium, we have 1s2, 2s2, 2p6,
which is the same electron
configuration for neon but
then we need to put one
more electron in there.
And that's gonna go in the three s orbital
and it's gonna be indicated by 3s1 so
we'll fill in completely fill the 1s and
the 2s and
we'll also completely fill up the 2p and
we have one electron in the 3s.
For magnesium, we need to add one more
electron to the sodium to give us 12 so
that's gonna be a 1s2 2s2, 2p6, 3s2.
So, we completely filled the 1s and
the 2s,
completely fill the 2p and
now we're gonna completely fill the 3s.
In aluminium,
we now need to add one more electron and
the next highest orbital
is gonna be i the 3p,
so now we have 1s2, 2s2, 2p6, 3s2, 3p1.
So we'll completely fill the 1s,
the 2s and
the 2p, we'll completely fill the 3s and
we'll put one electron in the 3p.
And as you can see when I'm filling
in In these orbital diagrams,
we're gonna start to see a trend, okay?
And that trend is that when I
go from aluminum, to silicon,
to phosphorous, to sulfur, to chlorine,
we're just gonna add one more
electron here in the p block.
So you're gonna start to see
a trend until we get up to argon,
which we need to put 18 electrons in.
It's gonna be 1s2, 2s2, 2p6, 3s2, 3p6, so
we're gonna completely fill the 1s,
2s, 2p, 3s, and 3p orbitals for argon.
So, we'll go ahead and fill those up here,
make sure we follow our appropriate rules.
And this is how you would write the block
diagrams for the first 18 elements.
And in the next video,
I will go through and
write out the electron configuration and
block diagrams for elements 19 through 30.
