Hello my favorite students. This is Ms. Weir
and i'm going to show you how to
get started on WS#4,
determining valence electrons. So, on
question one, I would like for you to
write up the electron configuration for
the following elements, then circle the
valence electrons.
Let's start with hydrogen. So, 1A,
hydrogen. You'll need your periodic table.
Hydrogen has atomic number one, so how
many electrons? One. Atomic number 1, so 1
proton and one electron and that electron
lives in level 1s and it's only one
electron. So 1s^1. Now, we've been
talking about in the 1s level, electrons
need to come in a set of two to be happy,
then we have a full orbital as long as
there's only one electron in our 1s
orbital; that is our valence electron. So,
go ahead and circle that. Now for
nitrogen, atomic number seven. So, we have
seven electrons. We're going to put seven
electrons into our Aufbau chart. So, two
can go on 1s, two more right here
one, two, three, four, five, six, seven, so your electron configuration
notation looks like this: 1s^2 because
two electrons live in the 1s orbital,
2s^2 because we have two in here, and then
in 2p, we have one, two, three. Now, in
class we talked about the 1s^2
level is happy when there are two
electrons in it. So, it's happy.
What are our unhappy valence electrons?
Do we have a set of eight here and the
level 2 we have two in the 2s and three
in the 2p for a total of five. Five is not
eight, so they're not happy, so these five
are our valence electrons.
So, for these problems right here
write out your electron configuration
notation and then go ahead and circle
the valence electrons and you can either
circle them singular or you know by
themselves or just scoop them together.
So, go ahead and do that for all of those
now then in number two, it is up to you
whether you write it out, if you use the
Aufbau chart. All I would like to
know is how many valence electrons these
elements have. In number three, you're
going to copy these or if you print this
out you can do it right on here. You see
the first ring right here is the 1s
level and then that's level 2 and chlorine
has a level three and boron has a level
one, two, three, four, and you are looking for valence
electrons and valence electrons are
those who don't have a set of eight. So, on
fluorine, on the outside level you have
one, two, three, four, five, six, seven. Seven
is not eight, so all of these here are
valence electrons and so do the same
thing for chlorine and bromine. Look at
the outside level and determine if you
have eight electrons on that outside
level. If yes, they're happy and they
should be a noble gas. If they don't have
a set of eight on the very outside energy
level then all of those are valence
electrons. And then in number five here,
this here is the same thing as doing the
Aufbau diagram, except for you don't
have the raised levels, right here we
have the 1s, the 2s, the 2p, right
here they're just side-by-side and so
for carbon, carbon has atomic number six.
You fill up the two electrons in the 1s
and then you put two more in 2s and
then you have two more because you need
six total. One, two, three, four, five, six, and the 2p
and how many valence electrons do you have? Well, in
the 1s, they're all happy if there
are two of them. So these are not valence
electrons. Do we have eight right here?
No, we don't so all of those are valence
electrons. So that's how you have four
valence electrons. So, go ahead and look
at helium, chlorine, lithium, all of these
you can use your Aufbau diagram if you
want to and then just transferred here
or you can place your electrons in these
levels on this sheet right there. And
then tell me how many valence electrons
you have. Alrighty,
any other questions, shoot me an email or
ask me in class and we will tackle this
together.
Thank you.
