# Atomic Number, Mass Number, and Net Charge

here's a diagram of an atom it's not perfectly accurate but for what we need right now it's going to do just fine so in this lesson we're going to look at characteristics that we can use to describe atoms like this one you know if somebody asks you to describe a person chances are you use characteristics like the color of their hair color their eyes what their height is and so forth just like that there are characteristics we can use to describe atoms the first of these
characteristics and maybe the most important is the

## number

is often abbreviated by a capital letter Z and what the

is is it's the

## number

of protons in the nucleus of an atom in my diagram here I'm using these red circles to represent protons so I have 1 2 3 protons in this atom so the

## number

is going to be 3 for this atom here

## number

is particularly important because the

## number

of protons in an atom tell us what kind of an atom is and by
that I mean is it a carbon atom is it an oxygen atom is it a sodium atom we're going to talk more about that in the video on isotopes so you don't have to worry about it for right now the next important characteristic that we can use when describing atoms is the

## number

often abbreviated by an uppercase a here

is the

## number

of protons plus the

## number

of neutrons in the nucleus of an atom people always get confused by

here's why

is the

## number

of protons so everybody always wants

to be the

## number

of neutrons but it's not it's a

## number

of protons and neutrons in fact there's not really a name for the

## number

of neutrons just the

## number

of neutrons an atom we just don't use it that often so anyway for

## number

we want to count all of these together 1 2 3 4 5 6 7 the

## number

of our atom here is going to be 7 now finally the third characteristic we're going to talk about here is probably the complex
and that's called net

## charge

I don't have a good way to define that

## charge

I mean I don't have a good definition so what I'm going to say here is it's how protons and electrons balance each other out let's talk a little bit more about this so net

## charge

is about how protons and electrons balance each other out so protons as you know have a positive

## charge

and electrons have a negative

## charge

so that means that if we have the same

## number

of protons and electrons in an atom
like I have right here three protons and three electrons I'm not drawing the neutrons here because we're not worried about here we have the same

## number

of protons and electrons they're going to balance each other out this three minus is going to balance out the three positive so we're going to end up with an atom that has a net

## charge

of zero because these two things balance out and we can call this atom neutral which means that it has no net

## charge

now what would happen in an
atom where we have four protons and three electrons we don't have the same

## number

of electrons and protons anymore so they can't totally balance each other out instead we have more protons than electrons so that we're going to have a net

## charge

that's positive because there's going to be some of this positive

## charge

in the protons it can't be balanced out by the electrons in this case we have one more proton than electron so this is going to give us a net

## charge

of plus
one since our atom has a net

## charge

we give it a special name we call it an ion an ion is any atom that has a net

## charge

neutral is what you call it if you don't have a

## charge

d ion is what you call it if you have any

## charge

okay this is where we have one more proton than electron what about this case here what if we had five protons and three electrons in this case the

## charge

s don't balance out either but now I have two more protons than electrons I've got two more protons that
aren't getting balanced out by these electrons so that means that I'm going to have a net

## charge

of two plus for these two protons and again this is going to be an ion because it's got a

## charge

now the opposite can happen as well here is an example where an atom has four electrons and three protons so now it's got more electrons and protons these three protons can only balance out three of the electrons so have one more electron that's not getting balanced down that means
that this total

## charge

is going to be minus one that's a

## charge

of this one more electron that I have in the proton and if I had a case in which I had five electrons oh I should have said we call this an ion because it has a

## charge

just like this negative

positive

## charge

it doesn't matter if it's got a

## charge

we call it an ion okay so anyway we have a case where we have five electrons and three protons now there are two more electrons and protons so I have two negative

## charge

s
that aren't getting balanced out by the proton which means that I have a net

## charge

of minus two and this also is an ion so that's how you can figure out net

## charge

so what's the net

## charge

for this end well we have one two three four electrons and we have one two three protons since there are different

## number

s the protons and electrons aren't going to be balancing each other out we have one more electron than proton so that means that we have a net negative

## charge

and since
there is one more electron than proton this atom here is going to have a net

## charge

of minus one so now that we've talked about these three characteristics you can use to describe an atom let's look at the practice problem video so you can go over this and a little bit more depth and try a bunch of examples