Name: Representing ionic solids using particulate models | AP Chemistry | Khan Academy
Uploaded: 2020-03-27T17:40:43.000Z
Duration: 5 min 43 s
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- [Instructor] In this video, we're gonna think about

Reflexive pronouns

let's say that we have a bunch of this white cation,

and we have a bunch of this green, or this blue-green anion.

So let's say they're in a one-to-one ratio.

How will the solid look, if you were to take

We're just imagining a two-dimensional slice of the solid,

and we're just drawing these ions as particles.

where maybe the positive ion is all on one side,

and then the negative ion is on the other side,

is on the bottom if we were to take a slice?

and then you have some negatives right over there.

And then, maybe you have a positive and a positive,

And then maybe you have some negatives right over there.

Would this be a reasonable configuration,

Well, when we think about Coulomb forces,

we know that like charges repel each other

and unlike charges, or opposite charges, attract each other.

or even in this way, because they're gonna form

in a way that maximizes the attractive forces

and minimizes the repulsive, the repelling forces.

And so what would be an arrangement that does that?

are gonna try to get as close as possible

to the negative charges and as far as possible

And the same thing is going to be true of negative charges.

and as close to other positive charges as possible.

So the arrangement that you are likely to see

is going to look something more like a checkerboard pattern.

I'm not drawing it perfectly, they'd be the same size.

And when you do these two-dimensional representations,

'cause we're gonna think about that in a second.

And then the negative charges would be in between.

every negative is surrounded by positives,

and every positive is surrounded by negatives.

and it's minimizing the repulsive forces.

And if you were to think about it in three dimensions,

Now another interesting thing to think about

is the size of the ions that form that ionic solid.

Let's say we wanted to deal with rubidium bromide.

What would this look like if I were to draw it

in a two-dimensional particulate model like this,

and I wanted to make the size roughly comparable

to what we would see between the rubidium and the bromide?

and I'll give you a little bit of a hint.

All right, if we were to separate this out into its ions,

it is a rubidium cation, and a bromide anion.

Now a rubidium cation, it has lost an electron.

its electron configuration now looks like that of krypton.

Now, the bromide anion, even though it only has 35 protons,

it's going to gain an electron to become a bromide anion,

and it also has an electron configuration of krypton.

So both of these have the same number of electrons,

but rubidium has two more protons than bromide does.

more than the bromide nucleus is going to.

And so if I were to draw one of these diagrams,

So I have a bromide anion, I have another bromide anion,