Hi. It's Mr. Andersen and this is chemistry essentials video 23. It's on ionic solids.
Over the next four videos we're going to talk about four types of solids. And what those
solids are depend on where their atoms are coming from. So on the periodic table, if
we were to draw a line like this. On the left side we're going to have the metals. And on
the right side, including hydrogen we're going to have the non-metals. And so if that solid
is made up of just atoms from the metals we call it a metallic solid. If it's only nonmetals,
but they're relatively small, we call those molecular solids. If they have large structures
of covalently bonded atoms, we're going to call that a covalent network solid. And in
this video we're going to talk about ionic solids which are a combination of metal and
non-metals. And so ionic solids remember are going to be made up of, or their structure
is made up of ions. Which are atoms that have either gained or lost electrons. They're
either cations or anions. And so they're put together based on these almost static
charges. And so how big those static charges are going to be based on Coulomb's law. And
so if they have large charges, it's going to have a better structure, or lattice energy
we call that. And if they're smaller it's going to have greater structure. And that's
because they're closer together, those charges are. And so what are some of the properties
that we observe in ionic solids? Well, they have a high melting point. They have low vapor
pressure. They're going to be very brittle. Break readily. And also they're going to be
poor conductors of electricity in a solid form. However if we were to melt them, they
can actually conduct electricity. And if we were to dissolve them in water and create
a solution they're going to conduct electricity as well. And actually making solutions of
ionic solids is relatively easy if we use something that's polar, like water. And so
what does an ionic solid look like? It looks like this. And so it's going to be this nice
lattice. And it's alternating ions. And so we're going to have anions like chlorine ion.
And then cations, like sodium ion. And what's happened is remember, you've transferred an
electron from one to another. And then they're held together by almost a static charge. And
this is an incredibly hard charge. And the reason why is that these are highly charged,
these different ions, and also they're really close together. And based on Coulomb's Law,
opposites are going to attract. And as we decrease that radius between them, we're going
to increase the charge between them. And so that's the structure. It's simply this nice
lattice of ions. And so then you should understand the different properties. And so what's one
big one? High melting point. Since these are attracted together at the really hard bionic
bond, we're going to have a high melting point. So this is salt right here. It's melting point
is 801 degrees celsius. If we look at sugar, which looks the same but it's actually held
together with covalent bonds, it's going to have a much lower melting point. They also
have a really low vapor pressure. What is vapor pressure? Remember if we put a liquid
in a container, the amount of atoms that jump off and form a gas is going to be the vapor
pressure, as they exert vapor pressure. And so remember the greater the forces are in
that liquid, or in that solid, the lower the vapor pressure is going to be. And that's
based on again these high attractions in the ionic bonds. It's also going to be incredibly
brittle. What does that mean? If we were to take, attach a ionic solid and just pull it
from the sides, it will break right in half. If we were to do that to a metal, it would
stretch. It's ductal. Why is it brittle? Well all of these ions don't like being next to
other ions. You can see that all of the chlorine ions are as far away from chlorine as they
can get. And as we start to force them towards them, they push back. And so that's why they're
going to be incredibly brittle. They can't conduct electricity because we don't have
a lot of free electrons around. It's simply locked into this lattice. However if we were
to melt it, and so this is a lithium fluoride, beryllium fluoride melted salt, it actually
starts to conduct electricity. And if we add it to water, it's going to quickly break apart.
And it's going to be an electrolyte. It's going to allow electrons to flow through it
as well. Why is it that we can breakdown ionic solids using something like water? Remember
water is polar. It's going to have partial negative charges on the oxygen side. And partial
positive charges on the hydrogen side. And so you can see that all the negative sides
of the water are going to be attracted to the sodium. And so they can kind of usher
it away from the ionic solid. Likewise on the chlorine ion what we're going to have
are the positive hydrogen parts are going to be attached to it. And that's going to
usher it away as well. Once we remove those water molecules, it goes right back to that
ionic solid again. And so did you learn two things? Did you learn to show a representation
of what an ionic solid looks like? And remember it's just going to be ions that are locked
together in a lattice. And did you learn the properties? The properties are simply built
on the structure. And I hope that was helpful.