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  • - [Instructor] What we have depicted here

  • in these four images are matter

  • in different states.

  • And we're using what's known as a particulate model.

  • And these are two dimensional particulate models

  • which are simple ways of imagining

  • what is going on at a molecular scale

  • inside of matter.

  • And so you can imagine each of these circles to,

  • depending on what we're dealing with,

  • it's either an ion,

  • it's a molecule,

  • or it's an atom.

  • But it's telling us how these molecules

  • or ions or atoms are interacting with each other.

  • Which determine what state of matter we are in.

  • So pause this video and think about

  • which of these quadrants represent matter

  • in a solid state,

  • which represent matter in a liquid state,

  • and which represents matter in a gas state.

  • All right, so there's a few that might have been

  • somewhat obvious to you.

  • If you imagine each of these circles to be an ion,

  • you could imagine these to be ionic solids

  • that we've seen.

  • That type of lattice structure.

  • If you imagine each of these circles

  • to be atoms that are forming covalent bonds

  • with neighboring circles,

  • then you could imagine this being

  • a covalent network solid.

  • If you imagine each of these circles are molecules,

  • and due to intermolecular forces,

  • they have arranged in this regular way

  • to the other molecules,

  • then you could imagine this is a molecular solid.

  • You could also imagine that each of these

  • are metal atoms and they're all sharing

  • the soup of valance electrons.

  • And so we're dealing with a metallic solid.

  • But no matter which visualization you use

  • or what you're imagining this to be,

  • it's pretty clear that this is a solid.

  • And one of the major giveaways of that

  • is that it's not taking the shape of the container.

  • These molecules, I guess you could say these particles,

  • aren't able to fully slide past each other

  • and take the shape of the container

  • that they're in,

  • which would happen in a liquid.

  • And they're clearly not able to overcome

  • the forces between the particles

  • to then go off and do their own thing,

  • which we would see in a gas

  • and bounce around the entire container.

  • So this is clearly a solid.

  • Now this one on the bottom left,

  • here it does look like the particles

  • are taking the shape of the container.

  • They are able to slide past each other,

  • but there are still intermolecular forces there

  • that keep them from flying apart.

  • So this is clearly a liquid.

  • And in this bottom right quadrant,

  • you could imagine what's going on.

  • These particles, whether they're molecules or ions,

  • they have for the most part

  • been able to overcome the intermolecular forces

  • between them.

  • And so they are just bouncing around,

  • fully taking the form of the container

  • that they are in.

  • And so this is a gas.

  • Now what about this right over here?

  • It looks kind of like a solid

  • in that it's not taking the shape

  • of its container.

  • But it's also irregular,

  • the way that you might expect a liquid to be,

  • at least at a snapshot in time.

  • And this, because it's not taking the shape

  • of its container,

  • and because these molecules or these particles,

  • even though they are irregular,

  • they aren't sliding past each other

  • like you would expect in a liquid.

  • This too is a solid,

  • but we call this an amorphous solid.

  • It does not have this nice crystalline structure

  • like we've seen with the crystalline solids.

  • And there's a lot of examples

  • of amorphous solids.

  • Most of the solids you know in your life

  • that are stretchy,

  • that have an elastic quality to them,

  • are amorphous solids.

  • For example, if you had a little bunch of natural rubber,

  • you could pull on it and it might look

  • something like this when you stretch it.

  • But then when you let go,

  • it will go back to its original state

  • or maybe close to its original state.

  • And the reason why it does that

  • is natural rubber is made up of polymers.

  • And just to imagine what a polymer is,

  • this is a molecular structure

  • of actual natural rubber.

  • It's a chain of carbons that are bonded to hydrogens.

  • And if you imagine it,

  • if you were to zoom out from this,

  • you imagine these chains,

  • these very long chains of carbons

  • with hydrogens.

  • And then in natural rubber,

  • they all get tangled up with each other.

  • And so they're forming this amorphous solid.

  • It doesn't look exactly like this particulate model

  • we just saw,

  • it's more just imagine a bunch of strings

  • that are all tangled up.

  • And so if you were to pull on them,

  • they are able to stretch,

  • but then you let go,

  • they get back to close to where they were before.

  • Now rubber isn't the only polymer.

  • For example, the plastics you see all around you

  • are also polymers.

  • And a few are mostly amorphous.

  • And then a few are mostly crystalline.

  • And a lot are what we would call semi-crystalline.

  • Which means they have both amorphous

  • and crystalline regions.

- [Instructor] What we have depicted here

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B1 中級

固體、液體和氣體的顆粒模型。 (Particulate models for solids, liquids and gases)

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    林宜悉 發佈於 2021 年 01 月 14 日
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