In this video I'm going to go over how
to find the charge of an ion and so it's
basically using the principles of the
octet rule and so let's just start by
looking at nitrogen and so nitrogen is
atomic number seven so the first fact we
have to know to find the charge of an
ion is that a neutral atom has the same
number of electrons as it does protons
which is same as the atomic number so
now we can figure out a nitrogen if it's
neutral we'll have seven electrons so
let's go ahead and draw in the electrons
around a nitrogen nucleus so here's our
nitrogen nucleus
and then we're going to have our first
orbital and so now we have to learn a
second factoid which is that our first
shell can hold up to two electrons
I'll draw those in now and then our
second shell can hold up to eight
electrons so for nitrogen we've filled
up this first shell with our two and so
now we're going to have to start
expanding into the second shell so I
ended up with five in the second shell
because we want a total of seven ok and
now let's define another important part
of these problems which is valence
electrons and so to do that let's define
the valence shell and the valence shell
is the last shell with electrons in it
and then the valence electrons are just
the electrons in that valence shell so
for this problem we've used two shells
in total and so it means that our second
one is our valence shell okay so right
now nitrogen has five valence electrons
because it has five electrons in that
last shell and so now we have to learn
the most important part of these
problems and that is that every atom
actually has a secret lifelong dream and
every atom on the periodic table has the
same exact lifelong dream and that dream
is to have a completely full valence
shell and so every atom all of its moves
that it does is just to get this dream
to happen it'll try to trade electrons
will try to get electrons it just wants
to do anything it can
to get a completely full valence shell
so it doesn't want any empty spots left
over in its valence shell and so if we
go back to our rules of how many
electrons each shell can have we can see
that our second shell can hold up to
eight electrons and our nitrogen only
has five in its second shell right now
so nitrogen views itself like this when
nitrogen is thinking about itself it
says alright I've got five electrons in
my second shell but what I really want
is three more because then that would
fill up my second shell and that would
mean that I achieved my lifelong dream
so for right now let's just say that
that nitrogen does end up fulfilling its
lifelong dream so let's say that somehow
it ends up getting three more electrons
okay so if this nitrogen gains three
more electrons then it will be
completely full so it'll still have its
two in its first orbital and then now it
will have a total of eight in its second
orbital completely filling it so before
when nitrogen just had its regular seven
electrons we'd say it was kind of
unhappy
but now that it's got its three more
electrons and its valence shell is full
we'd say this is happy its fulfill its
life form goal okay so now let's get
into the charges of these nitrogen atoms
before and after they got a full valence
shell so the way that we determine the
overall charge which is the same thing
as the ion charge of an atom is to add
up the charge of the protons plus the
charge of electrons and that just is the
overall charge so before the nitrogen
got its change before it got its three
extra electrons the charge of the
protons was plus seven and that's just
because that's the atomic number that's
always how many positive charges
nitrogen will have and so we'll add this
to the charge of electrons this is all
before the change and so this is when
nitrogen just had seven electrons and so
when that was the case it had a charge
of negative seven coming from the
electrons and that's why we said we had
a neutral atom because positive seven
plus negative seven is just zero so it's
a neutral atom and so now let's look at
it after the change and so the charge of
the protons is still exactly the same
right it still has positive seven
nitrogen will always always always have
positive seven because the protons the
number of protons never changes that's
just the same as the atomic number all
the time so now it doesn't have seven
electrons anymore
it has ten electrons because it had
seven and then it got three because it
got its life point because it achieved
its lifetime goal so now the negative
charge this nitrogen has is negative ten
so when you add those two together
positive seven plus negative 10 you get
an overall charge of negative three and
this is our ion charge and so the way we
would write that is to have our atomic
symbol N and then we'll just do a three
minus and so this is how we indicate to
people that we have a nitrogen ion that
has a charge of negative three and so
just another vocabulary word if you have
a negative ion that means that you have
an anion all right so now that we've
done that example let's do another
element so now I want to look
at sodium and sodium is atomic number 11
and so let's go ahead and draw out our
electrons for sodium just like we did
with nitrogen so we'll use our first
rule to know that a neutral atom has the
same number of electrons as it does
protons same as the atomic number so
we're going to draw an 11 electrons for
sodium so we fill up our first orbital
with two we aren't done we have to show
11 electrons so we go to our next one
and we fill in it this one actually gets
completely full because it can only fit
eight which means now we're at a total
of 10 and we still have that one more
electron we have to indicate because we
have to get to 11 so that means that
we're going to go into our third orbital
and so we have one more and by the way
I'm only showing the first second and
she'll here today that's all we'll do in
this tutorial but with a lot of other
shells that come after that that have
their own rules okay so now we have our
sodium and so to predict how sodium is
going to react we actually have to learn
two more little addendums to the
lifelong dream of every atom and so the
first one is that atoms don't care how
many orbitals they have so if the sodium
has one two or three or more it's happy
as long as that last one is full and the
second addendum is that it's the same
amount of work to gain or lose an
electron so sodium right now it has its
three orbitals and we know that it wants
that last one to be full that's ass life
long dream so its last one its third
shell can hold up to eight electrons
which means that it only has one right
now so it could have seven more so
sodium could be happy by adding seven
more electrons but that's a lot of work
it's a lot of work to get seven
electrons it's way easier to just lose
that one electron because it's a same
amount of work to gain or lose an
electron so sodium is just going to say
I'm not going to even bother trying to
collect any electrons I have to get
seven that's way too many what I'm going
to do is just get rid of this one and so
let's again just save right now that the
sodium gets its lifetime goal and
it's able to just lose one electron then
it would look like this we'd have our
sodium nucleus it have its - we'd have
to go to our second orbital and now when
we got to our third orbital we wouldn't
have anything to put in it because
remember it only had one to begin with
and then in this case sodium got rid of
that one so in this case now sodium
would no longer be using its third
orbital so the second one will become
the valence shell or the valence orbital
so now this is using the first addendum
to that rule because sodium is
completely happy now it doesn't care
that it used to have three orbitals and
now it just has two it's like I'm super
happy just because I'm totally full at
this second one so that's what I always
wanted
okay so now let's do the same thing we
did before we calculate the charge
before and after our change so before
the change we had plus 11 coming from
the protons that'll always be how many
we have from the protons because sodium
can never change number of protons it's
just going to be the atomic number and
now the charge of the electrons before
the change it had 11 electrons so a
charge of negative 11 so it's overall
charge used to be zero that's when it
was a neutral atom and so now let's look
at it after the change and so charge of
protons again we can never change this
number that's just going to be 11 and
now plus so it used to have 11 and it
lost 1 to get full down to 10 so now it
only has a charge of negative 10 because
it only has 10 electrons so now when we
add positive 11 plus negative 10 we get
an answer of 1 and because it's
chemistry we always say plus 1 we never
just say 1 because we won't really want
to tell people is it positive or
negative
we don't want to leave a blank anymore
and so we can write this ion like this
sodium plus 1 or because the charge is
dust just 1 you can just say na and then
plus you don't have to say a number if
the number is 1
okay and because we have a positive ion
that's called a cation and I like to
remember that because the tea looks like
a plus sign so positive all right so
these are our rules and so now let's get
into some overall trends and learn how
to do these problems a little bit faster
all right now that we've seen how I ons
are formed let's make some overall
trends so if we look at the periodic
table we can actually break down the
shape of the periodic table by number of
valence electrons and so everything in
this first column on the Left has one
valence electron and everything on this
second column has two valence electrons
and now we get to all these transition
metals and you cannot predict how many
valence electrons these are going to
have it's not possible with this rule so
don't worry about any of these elements
and now we're over here starting at
boron this is our third column and
everything in this third column has
three valence electrons and the trend
continues for the rest of the periodic
table all right so going all the way
until we get to the noble gases the very
last column on the right-hand side that
all have eight valence electrons except
for helium which has two okay so now
let's learn the trends of what elements
with different numbers of valence
electrons do when they're forming ions
so the first is that anything on the
left-hand side the first to the third
column if you have one to three valence
electrons you want to lose electrons
until they're at zero because remember
these are the ones like sodium where
it's easier just to lose all electrons
rather than try to gain a bunch okay and
then so next I want to talk about things
like nitrogen and so if anything has
five to seven valence electrons they
want to gain electrons until they're at
eight because these are the ones that
are really close to having eight
electrons and so it's easier for them
just to pick up a couple more electrons
then try to ditch all the ones they
already own okay so now just two more
columns you can see we haven't said
what's going to happen to anything that
has four valence or eight family
so let's start with 8 valence now these
are the ones that are completely happy
already they've already achieved their
lifelong goal they have a completely
full octet so they're not going to do
anything there's no motivation for them
to do anything if they lose an electron
to become unhappy if they gain an
electron they become unhappy and right
now they're completely happy as so these
are our neutral elements and then our
last one is 4 electrons and these are
right on the edge so it's just as much
work to gain 4 electrons as it is to
lose 4 electrons so just depending on
the reaction or depending on what the
circumstance is it will either gain or
lose 4 so you won't be asked to predict
it if you just said carbon will gain or
lose you know one would ask you to do
that they have to give you some other
piece of information that then would
tell you what carbon or silicon or any
of these ones would do so going along
looking at the parentheses that I have
if you have one two three valence
electrons you want to lose and you
become a positive ion because remember
any time you're losing electrons you
become positive so then four valence
electrons you'll become negative or
positive depending on if you lose or
gain five to seven you become a negative
ion because you're getting something
that's that's negative you're getting
more electrons now then you have protons
so you're going to be overall negatively
charged and then eight valence electrons
they're not doing anything so they
remain neutral they always have a charge
of zero okay so now that I've gone over
these trends let's just do a couple of
more practice problems so let's predict
the ions for calcium and arsenic and so
what will the ion beam starting with and
these are I'm doing these problems with
the most steps so you can do these
problems a lot shorter if you know how
but I just want to explain it for people
that are completely confused this is how
you always always always can get it
right and you understand why you got it
right so calcium how many electrons does
this atom have when it's neutral so step
one find it on the periodic table it's
right here and so that means it's going
to be the same as the number of protons
so it means that when it's neutral this
has 20
electrons so now how many valence
electrons does Adam have when it's
neutral so we can just see it's in our
second column which means it has two
valence electrons so two so now how many
electrons does this element want to gain
or lose and this is where we look down
here to our 1 2 3 valence electrons
rules and so this is in the category of
having 2 so it's going to lose until
it's at 0 and so this wants to lose two
electrons that's what it really wants
and remember even though I say it loses
2 until it's down to 0 what I really
mean is that it loses it until that
shell happens to be gone and then the
shell under it is completely full so
it's not like calcium by losing two
electrons will now have no electrons
left over it'll still have 18 when it
loses so now let's just solve out these
ions again just showing it with every
step to show you where the charge really
comes from so what will the ion be for
these atoms charge of charge of protons
plus charge of electrons equals the
overall charge so the protons always
going to be a charge of plus 20 and now
the charge of the electrons when it's
neutral before the change it has a
charge of negative 20 it's the same as
the protons and so the overall charge
when it's neutral is 0 which will always
be the point of this is just to see
where the overall charge is coming from
and so now after the change we still
have the same number of protons and so
our calcium wanted to lose two electrons
so now it only has 18 electrons so when
you add positive 20 plus negative 18 you
get positive 2 and so this is the ion
charge for calcium so if we write it up
here it will be calcium 2 plus and then
this will be a cation and then one more
practice problem we have arsenic so
starting by just finding it on the
periodic table it's right here number 33
so this electron 1 has 33 electron this
element has
33 electrons when it's neutral so how
many valence electrons does it have when
it's neutral when it starts off and we
look in the column we just look up it
has five valence electrons so what does
it want to do we can go down to this
rule because it's in the category of
having five to seven it wants to gain
electrons until it's at eight so it
wants to gain and it takes three to get
from five to eight so now calculating
the ion charges so before the change
we're going to have a charge of plus 33
from the protons plus negative 33 from
the electrons and so we start off as
zero and then after the change we're
going to have always the same number for
protons plus 33 and then it's going to
be plus and now it's gained three more
so instead of having 33 it'll have 36
electrons so now positive 33 plus
negative 36 is negative three so this
will be our ion charge for arsenic
arsenic three minus and this will be an
anion and so now we've done a couple of
these practice problems the long you
know way where we show everything we can
actually make some more general trends
about the periodic table because
everything in this first column back
over to one valence electron will create
an ion with a charge of plus one
everything in the second column will
create a charge of plus two because it
loses two electrons everything in this
third column will create a charge of
plus three everything in the fourth
column will create a charge of plus four
or minus four depending on if it loses
their gains
everything with five valence electrons
this is where it flips because this is
where it starts to gain this will create
charges of negative three six valence
electrons
this creates charges of negative two
seven creates charges of negative one
and then eight valence electrons they
don't want to do anything so they just
remain neutral they have a charge of
zero all right I hope this extensive
showing every step way
what anion and how to do valence
electrons and total electrons helped you
guys please try remember this it's
something that a lot of people struggle
with but once you understand it it's
really not that bad and so many other
types of chemistry problems start to get
unlocked for you alright
happy studying okay
