In this video I'm going to talk about
how to find the number of protons
neutrons and electrons in both neutral
atoms and in ions which are atoms that
have a charge okay so if we start with
nitrogen on our grid the first thing we
do with all of these is to find that
element on the periodic table so if we
look at this we can find nitrogen
towards the top right right here and if
we were to zoom in on just the square of
nitrogen on the periodic table we'd see
something like this and so we usually
have these four pieces of information
and our number on top that's our atomic
number and the atomic number is equal to
the number of protons so this answers
our first question nitrogen has seven
protons and nitrogen will always have
seven protons this is the one number
that never changes
it always is going to be until the end
of time that every nitrogen has seven
protons that's the definition of
nitrogen so it's like kind of like the
social security number of an element is
the atomic number all right so next
we're asked how many neutrons does
nitrogen have and for this we're
actually going to have to put a question
mark because we aren't given enough
information in this problem to know what
this particular nitrogen atom has and
not every single nitrogen atom has the
same number of neutrons so that's based
on something called the mass number that
we'll get to a little bit based on the
periodic table the only information
about the mass of this nitrogen is just
the general atomic mass which is our
number on the bottom it's a decimal
point and the atomic mass is just the
average mass of that element so it
doesn't really help us tell how heavy
this particular nitrogen atom is so we
can't figure out how many neutrons it
exactly has all right so next we have
the number of total electrons and so for
this we'll have to learn this piece of
information which is that a neutral atom
has the same number of electrons as it
does protons which is the same as the
atomic number so if you aren't told
anything about an atoms charge you can
assume it's neutral and so in this case
it means that our nitrogen is just going
to have
seven electrons because it's the same
number as our atomic number all right
and so then lastly we have to do the
number of valence electrons which is
just the number of electrons on that
last orbital that has any electrons in
it and so for this we're going to use
our overall trend and so the trend is
that starting on the left-hand column of
the periodic table everything in this
column has one valence electron and then
the second column has two valence
electrons so everything in the second
column has two valence electrons and
then getting to these transition metals
these you cannot predict with these
trends nothing in here you can just look
at and know exactly how many valence
electrons you have and then by the time
we get over to this third column this
has three valence electrons and we just
fill this in until we get to the end
all right so now we can just using our
trends see that nitrogen is in the fifth
column so it's going to have five
valence electrons and so everything in
this column would also have five valence
electrons
all right let's now go to an element
that's written a little bit differently
so we have sodium and then a dash and
then the number twenty okay so first of
all we can always find the number of
protons just by identifying this element
on the periodic table so we look for a
sodium that's abbreviated a we find it
right here on the left hand side and so
sodium is number eleven so atomic number
that's always your number of protons so
sodium will always have eleven protons
and now we can actually find the number
of neutrons so if we bring this problem
over to our bottom right here we can
identify this number so when elements
are written like this the full element
name - then a number that's actually
talking about the mass number and so the
mass number is the number of neutrons
plus the number of protons because those
are the two particles that make up the
huge huge huge majority of a mass of any
atom okay so if we want to find the
number of neutrons then all we have to
do is to subtract the mass number minus
the atomic number which is the number of
protons and that will give us our number
of neutrons okay so to plug this into
this formula
remembering that whenever we see
something with that - that means the
mass number so now this is also talking
about just this sodium atom not sodium
atoms in general so for just this sodium
atom it has a mass number of 20 and then
we're going to subtract the atomic
number so 11 and so we're going to get
nine and so this particular sodium atom
has nine neutrons okay so now let's find
the number of total electrons so again
we weren't given any information about
the charge so we're going to assume it's
neutral so that means that it has the
same number of electrons as it does
protons so eleven and now to find the
number of valence electrons
so sodium's in our first column right
here and so everything in that column
only has one valence electron all right
so now going to our next example does
have a lot of stuff going on it's
written a little bit differently than
our other example so let's do bring it
down to the bottom right and define it
so when you have anything written like
this the number to the top left that's
just the mass number once again and the
number on the bottom left that's just
the atomic number which we can double
check by looking up selenium on the
periodic table and it's right here
number 34 and then we have our atomic
symbol s e and then our number to the
top right that's our charge and so
charge is just the number of protons
minus the number of electrons all right
so with all that information let's start
going through and seeing how many
particles we have of each one so number
of protons that's the easiest it's just
going to be that atomic number 34 number
of neutrons again we have to subtract
from the mass number so we're going to
have seventy minus 34 so we get a total
of 36 total number of electrons now this
is the first one when we do have
information about the charge so our
charge is negative two which means you
have two more electrons than you do
protons so we have 34 protons and so
each electron is negative so if we have
two negative we have two more electrons
and we do protons so this is going to
mean that we have 36 electrons and now
to find the number of valence electrons
well we can find how many valence
electrons a neutral selenium has just by
looking at the periodic table and we see
this in that sixth column over here so
that means that normally it has six
valence electrons but remember our
selenium has a charge of negative two
which means it has an additional two
electrons so this guy has a number of
eight valence electrons all right let's
go and do an example similar to that so
we have
our next symbol and so once again number
of protons that's the easiest this is
just going to be our bottom-left number
eight also on the periodic table
oxygen number eight so eight protons and
so number of neutrons 17 the mass number
for this particular oxygen atom minus 8
equals 9 this particular oxygen has nine
neutrons so now the total number of
electrons there is no charge indicated
which means we're going to assume it's
neutral and so we just look to the
periodic table and it has eight protons
which means if it's neutral it's going
to have eight electrons and so now the
number of valence electrons we can again
just look the periodic table and we see
the oxygen just like selenium was is in
that sixth column so it's going to have
six valence electrons all right a few
different wordings now we have carbon -
13 and we're just told this has a charge
of negative 3 so first of all look up
carbon on the periodic table it's right
here number 6 so it has six protons
number of neutrons 13 minus 6 so that's
a total of 7 neutrons and then we have 4
total number of electrons we know that
normally if it was neutral it would have
6 electrons to cancel out all those
protons and we know that this has a
charge of negative 3 so it must have an
additional 3 electrons so this guy has 9
total electrons all right and the number
of valence electrons so normally carbon
is in that 4th column so normally it has
4 valence and we know that this has an
extra 3 electrons so we have 4 plus 3 so
this carbon has 7 valence electrons all
right so now we have silver - 87 so
looking up silver it's down here number
47 so it has 47 protons and then for a
number of neutrons we do have our - and
the number and remember that equals our
mass number so we have 87 - 47 so we
have a total of 40 neutrons and so now
to get our number of total electrons
we are just going to assume it's neutral
because we're not told anything about
the charge so that means that it has the
same number of protons and electrons so
47 and now for a number of valence
electrons we're going to have to put a
question mark because remember this is
in our area where we cannot predict how
many valence
how many are going to be in any of these
elements it can really vary that's why
you can't predict dead ok so now our
last example we have number of protons
going to be 8
that's our atomic number number of
neutrons 16 minus 8 and now we're just
told this has three valence electrons so
let's look to where oxygen is now it's
over here at eight and so filling in
three valence electrons now how we're
going to get our number of total
electrons all right well we know that
oxygen usually has eight electrons and
we know it only has three valence
electrons the question is how many
valence electrons does it normally have
and then what's the difference and so
it's in that sixth column so normally it
has six electrons electrons so if it
only has three it basically has three
less electrons than it normally does so
then overall it has eight electrons
normally so minus three overall now it
just has five electrons and only three
year valence all right I hope you guys
learned how to find some particles and
different strategies I hope some are
useful and have a good studying
