States of matter
States of matter follow-up More on Plasma and Hydrogen bonds.
States of matter follow-up
- In the last video we touched on the three states of matter
- that are really most familiar to our everyday experience.
- The solid, the liquid, and the gas.
- And I kind of hinted that there is a fourth state, which
- I don't cover, because it's usually not the domain of an
- introductory chemistry course.
- But a little bit of a discussion ensued on the
- message board for that video.
- So I thought I would at least touch on that fourth stage.
- And that's plasma.
- I'll do it in a suitably bright color.
- And people consider it a fourth state because it has
- some properties of gases.
- In some ways it's almost a subset of gases.
- But it also has properties of conductivity that you normally
- wouldn't associate with a gas.
- And just so you know, when you first hear it you think, oh
- that's a fairly exotic thing, plasma.
- And in the first video, I said it's only something that
- occurs at high temperatures, which isn't
- exactly 100% right.
- It doesn't have to be at high temperatures.
- I really should have said that under extenuating
- circumstances where you have a very strong
- electromagnetic field.
- Or something has to happen to essentially bump the the
- electrons, or move the electrons off of gases that
- would've otherwise have kept their electrons.
- So it's kind of analogous to what happens in metal.
- When we talk about metal bonds, we talk about this
- notion of a sea of electrons.
- Let's say if we talked about iron.
- What happens with most metals is that they have so many
- electrons, and they are so willing to give them, that the
- electrons just kind of float outside of the atoms
- themselves and create this kind of big sea of electrons.
- And then the atoms themselves become
- positively charged ions.
- Because they essentially donated some
- electrons to the sea.
- So they're attracted to the sea and that's what makes them
- malleable and even more importantly what allows them
- to conduct electricity.
- But they're all really packed closely together and it's a
- very dense structure.
- Plasma is a situation where if you take gases, and remember,
- in gases things are pretty far apart.
- So you take a bunch of gases and they have
- high kinetic energy.
- Although, they don't have to be, that could be under very
- low pressure.
- But they're moving around and bumping into each other.
- But they're not close to each other.
- They don't have a fixed structure with each other.
- Or they're not rubbing against each other like in
- the case of a liquid.
- But what happens in a plasma, or one situation is, that you
- apply such a strong electromagnetic field that the
- electrons want to disassociate.
- So let's say these electrons start
- bumping off of the plasma.
- And so a solid has its own shape.
- A plasma will take the shape of its container like a gas.
- And sometimes it is described as an ionized gas.
- And it's described as ionized because
- electrons are bumped off.
- And when the electrons are bumped off, the otherwise
- neutral atoms now have positive charges.
- And what this allows is, essentially a conduction of
- Because now these electrons are free to move.
- You might say that sounds like a bizarre state of matter,
- where does it exist?
- Well, probably closest to home, it exists in lightning.
- And that's worthy of an entire video.
- But the idea is that you start having a huge potential
- difference between the clouds and the ground.
- And then because you have this huge voltage difference
- between the two, you have electrons that are essentially
- wanting to go into the ground.
- You have a build-up of electrons up here that want to
- go into the ground.
- They can't because air is normally
- a fairly bad conductor.
- It's an insulator.
- But what happens is because there's so much
- electropotential here, the electrons that are close in
- the molecules up here, at least how I visualize it,
- their electrons want to escape from these clouds.
- So their electrons start to want to move
- away in the air molecules.
- Whether you're talking about the air is a mixture of
- oxygen, and nitrogen, and carbon dioxide.
- They start wanting to get away from the clouds.
- So they start disassociating and start forming
- this ionized air.
- And eventually, at some point, this happens to such a degree
- that you can actually get conduction from the cloud to
- the ground.
- And that conduction is when the air is in a plasma state.
- The conduction allows extremely high temperatures
- and the electrons to flow all the way to the ground.
- The other common example, you might see something like this,
- well actually not like this, but at least a plasma state,
- is in stars.
- And that's because you have extremely strong
- electromagnetic fields, extremely high pressure, and
- in that type of environment, once again, I'm super over
- simplifying it, you can get to a state where the electrons
- can get disassociated from things that otherwise wouldn't
- want to give up their electrons.
- I thought I would touch on that because it's an
- interesting subject.
- And it exists in the universe.
- On the universal level, because stars are pretty much
- all plasma, it is actually the most common state of matter in
- the universe.
- Although in our everyday life, we probably encounter solids,
- liquids and gases a lot more.
- And one other thing I want to maybe clarify from the last
- video is, I talk about the bonding
- between water molecules.
- And let's say we're talking in the solid state.
- So I have an oxygen, a hydrogen, a hydrogen.
- And I have some electrons here, some electrons here.
- Let's say there's another hydrogen here, an oxygen, and
- a hydrogen.
- Maybe there's an oxygen here.
- That has hydrogen.
- And then this has a hydrogen.
- And it has two electrons, two electron pairs.
- So I talked about the notion, and we talked about it many
- times before.
- That oxygen is so much more electronegative that it hogs
- the electrons.
- And so the oxygen side starts to have a
- partial negative charge.
- While the hydrogen side starts to have a
- partial positive side.
- Because with the hydrogen, essentially all of its
- electrons are hanging out close to the oxygen, hydrogen
- ends up just becoming like this proton that's
- floating out there.
- Because we said it doesn't even have
- neutrons in most cases.
- So this has a slightly positive charge.
- This one has a positive charge.
- And the positive polar end of the water molecule is
- attracted to the negative polar end.
- And I called it polar bonds, and it shows you my memory
- from high school chemistry is not ideal, I really should
- have called it hydrogen bonds.
- So this is a hydrogen bond, and this is a hydrogen bond.
- It's just a matter of the name I used.
- I just want to clarify that because that is what's
- typically used in your chemistry class.
- I don't want to confuse you.
- And that is just the bond that exists from a partially
- positive hydrogen atom.
- Because its electrons are hanging out near the oxygen.
- And a partially negative oxygen atom
- in the water molecule.
- Because it has stolen all of these
- electrons from the hydrogen.
- You draw it like that, it's called a hydrogen bond.
- And hydrogen bonds tend to form between hydrogen or
- really only a handful of super electronegative atoms. And
- that's nitrogen, fluorine, and oxygen.
- And these are actually the three most electronegative
- atoms. So the nitrogen, NH3, when it bonds with hydrogen,
- is essentially so electronegative that you have
- the same situation.
- All the electrons hang out here, so you have a partial
- negative charge, partial positive on the hydrogen ends.
- Same thing with hydrogen fluorine.
- You get the same HF.
- You get the same type of hydrogen bonds.
- And so in this case, these guys would be attracted to the
- nitrogen part of other molecules and would form
- hydrogen bonds.
- I just want to get that out of the way.
- And with that done, I think we can return to some of the
- ideas of the last video and actually do some problems.
- Let's take the case with water.
- Actually, let me just state the problem first. So let's
- say that we have a
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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When naming a variable, it is okay to use most letters, but some are reserved, like 'e', which represents the value 2.7831...
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This is great, I finally understand quadratic functions!
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At 2:33, Sal said "single bonds" but meant "covalent bonds."
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