Week 1: Ions and Determining Charges

>Okay, so this video is gonna tell you
how to determine the charge on an ion

given the number of protons and electrons;

determine the number
of electrons given a charge;

and we'll talk about multiple ways

for us to demonstrate
what is happening with an atom.

What is it's mass? What is its charge?

So remember, the charge of an atom
is the number of protons.

Protons have a plus charge.

And we subtract the number of electrons.
They have a minus charge.

When an atom is charged,

and if it has an uneven number
of protons and electrons,

we call that an ion.

It's an ion.

That's an important definition.

When I have an ion,
it has unequal protons and electrons.

So let's calculate the charge
on the same element.

So I have this element.
It has eight protons.

If you looked it up on the periodic table,
you'd see it's an O; it's oxygen.

It has eight protons and eight electrons,

so I have eight pluses (eight protons)
minus an even number of electrons.

They cancel each other out,
so the charge is 0.

However, if oxygen
(it's eight protons)

has nine electrons,

I'd get a minus 1 [-1].

Now let's do a check. Electrons:
What's the charge on an electron?

It's a minus 1. If I have more negatives

than positives, I have
more negatives than positives,

I'd better have a minus charge.

And yes, I do. Okay, good.
Conceptually, that makes sense.

When an atom has eight protons
and seven electrons, the charge is--

So I have 8 minus 7,
that gives me a plus 1 [+1].

Now, does that make sense?

I have more pluses than minuses,
so I better have a plus charge, and I do.

Okay, yay.

Don't forget to check for mistakes.

Just make sure that the concept
works with the way you calculated it,

because sometimes people flip
the order of those two things.

Okay, so here is one way

for us to show the charge and the mass
and the number of protons of an atom.

Here, we have the atomic symbol nitrogen
('N' is for nitrogen.)

This is a minus 2 [-2].

Sometimes they put
[the negative sign] behind it,

sometimes they put it in front of it,

but that shows us the charge.

This [14] shows me the mass,

and this [7] shows me
the number of protons.

So from this information,

we can determine the number of protons,
neutrons, and electrons very easily,

so let's just show you how.

Nitrogen 14, 7, a minus 2 charge.

So we know, I find the smallest number.

The smallest number here
between the 7 and the 14,

this is the number of protons.

But you could also check
on the periodic table

and you'd know it's the number of protons.

The large number is the mass,

and we have our charge [-2].

So we can calculate the number
of protons, neutrons, and electrons easily.

Actually, we just need to do protons
and electrons by using our formulas.

So we know that the mass equals
protons plus neutrons.

We know the mass is 14,
the number of protons is 7,

and neutrons is what we want to know.

Subtract 7 from both sides,
and you're gonna get 7 neutrons.

Okay, so I can use the mass
to figure out the number of neutrons.

What if I want to know the charge?
So let's do the charge.

What is the formula for charge?

Charge equals the number of protons
minus the number of electrons,

so P before E (like "P.E.").

That charge is minus 2,
the number of pronouns is 7,

the number of electrons
equals a question mark.

So if I want to know this,
I subtract 7 from both sides

and I get the number of electrons
equals a minus 9.

You are allowed to use your calculator

if stuff like this is uncomfortable
for you doing them in your head.

Okay, so let's do a check.
Does this make sense?

If I have 7 protons (so 7 pluses)
and 9 minuses,

I have more electrons;
that would give me a minus 2 charge.

Okay, I'm feeling good about it.

Now you get to practice,
so I'm gonna let you do this on your own.

Okay, so let's just talk about two terms.

Ions: What are ions again?

They are things that are charged.

They have an unequal number
of protons and electrons.

Okay, cation.
I love that it has the 't' in there.

ca, t, ion, [the 't'] actually
looks like a plus [+]

so it's an ion and it has a plus charge,
and I think the 't' kind of looks like a plus,

so cations have plus charges.

And anions (it's the only thing left, right?)
are minus charges.

Minus charges, okay?

So two new terms:

Cations have a plus charge
and ions have a minus charge.

Take a minute to go through these

and ask yourself
these true or false questions.

[no spoken audio]