Here's an atom.
What is the atomic number, the mass number and the net charge to this atom?
So the atomic number is the number of protons.
In this diagram, these little red circles are representing protons here in the nucleus
so we’ve got 1, 2, 3, 4, 5 which means my atomic number is 5.
That was easy enough.
Mass number is the number of protons plus the number of neutrons which are these things
in blue so mass number is 1, 2.
3, 4, 5, 6, 7, 8 protons plus neutrons.
So mass number is 8.
Sometimes people think you have to have the same number of protons and neutrons in the
nucleus of an atom, definitely not true, they can differ quite a bit.
The net charge is how protons and electrons balance each other out.
So, electrons are represented by these things here flying around the outside the atom, 1,
2, 3, 4 electrons, e- is a way that we can abbreviate electrons, and 1, 2, 3, 4, 5 p+,
protons.
So, the protons and the electrons don't quite balance out.
There is one more proton than electrons so that one extra proton is going to give me
a net charge of 1+ because each proton has a positive charge have one extra proton.
Net charge of 1+.
This is kind of a basic problem, now we’ll move on to something that's a little trickier.
So here, we’ve got and atom with this atomic number, this mass number, and net charge.
From this information, we need to figure out the protons, neutrons, and electrons that
are in this atom.
Protons, that is going to be easy because protons… the number of protons is going
to be the same thing as atomic number.
So it's going to be 7.
Now what about neutrons?
Mass number is protons plus neutrons so this 15 here is protons and neutrons together.
I already know how many protons there are so I can do protons plus neutrons, the mass
number, minus the number of protons equals 8, the number of neutrons.
The net charge here is 2+.
If I have a positive net charge with a certain number, that's telling me how many more protons
I have than electrons.
So in this case, net charge of 2+, there are 2 more protons than elections.
Since I have 7 protons that means that I have to have 5 electrons for me to get a 2+ charge.
Here's a table with various characteristics of a certain atom.
We need to fill in the things that are empty.
Okay, we don't know how many protons, we don't know how many neutrons, where can we start?
Okay, we know the electrons and we know the net charge so based on the number of electrons
and the net charge this atom has, we can figure out how many protons there are, okay?
Since this is a net charge of -3 that means that there are 3 more electrons than protons
because electrons have a negative charge.
So I have 7 electrons that means I'm going to have…
I'm sorry if I had 10 electrons that means that I'm going to have 7 protons, 3 more electrons
will give me -3.
Okay, now I know that my atomic number is the same as my number of protons so that is
also going to be 7.
The mass number here is the number of protons plus the number of neutrons.
So to get just the number of neutrons I take a mass number, protons plus neutrons, minus
the number of protons, 7, and that is going to give me 9 neutrons.
Sometimes these table problems can be the hardest so we’ll do one more example.
Here, we want to find the electrons, protons, and the atomic number.
We know the neutrons, the mass number, and the net charge.
Okay, let’s start with protons.
We know the mass number, protons plus neutrons, and we know the number of neutrons.
So that means we can take 25, which is protons plus neutrons, and subtract the number of
neutrons, 25 minus 11 is going to give us 14, and that is the number of protons alone.
Atomic number is just another word for the protons, so these both are going to be 14.
Now that we know the number of protons in the nucleus, we can use the net charge to
figure out the number of electrons.
So it’s a net charge of 1+ which means that there should be one more proton because it
has a positive charge… one more proton than electron.
So 14 protons that means that total I'm going to have 13 electrons.
So now that you know how to solve problems like this, you're ready to go on to videos
about isotopes.