How to Find the Number of Protons Neutrons and Electrons!

How to Find the Number of Protons Neutrons and Electrons!


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

14 thoughts on “How to Find the Number of Protons Neutrons and Electrons!”

  1. I just graduated with my BS in chemistry and now studying for my MCAT and I forgot how to do the simple little thing ….

  2. Thank you so much i have a big chemistry exam tomorrow and I wasnt ready but this video truly got me caught up ❣

  3. Im teaching myself chemistry with a whole bunch of online tutorials which are amazing…but one thing i can not seem to figure out is… if we can't physically see atoms or subatomic particles… how exactly do we know how many protons, neutrons and electrons are in these atoms? And also is it possible to boil down to just one atom? have we ever measured just for say one hydrogen atom? Or are we just doing all these measurements and then scaling down to figure out the number of protons neutrons and electrons inside an atom?

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