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

beautiful video

Good video! Helped me so much! 😄

utem ko eshi kitora

The answer is -5

How to find atomic mass ?

Thanks so much for this!!!!!!! I have a chem exam tomorrow and i feel more prepared!! Thank you!

i thought # of protons and electrons were the same?

Thanks soo much i was gona fail 🤩

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

What is the avagadro number…

Really helped me thx a lot Robin😄

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

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?

Thanks