You sure that solid is a state?

[Thrilla]

I'm pretty confused with what I learned in school lol:

1. molecules in a solid state are tightly packed; molecules in a liquid state are not as tightly packed as liquids; then gas are moving pretty much freely.
2. When water freezes, it expands, same with gallium. (What happened to even more packed molecules?)
3. You can take a gas, compress it, cool it, and it'll condense into a liquid, but you can't compress a liquid into a solid.

:confused: I'm just wondering lol, someone give me an explanation.

[DTU_XaVier]

I'm no expert, and it's quite a few years since I've had those lessons, but here goes:
Water is simply an exception to the rule... I can't remember the exact explanation..
The best example I can give, is metal... You can't compress metal into a solid state either, you have to cool it... The most important thing to remember is, with materials which are liquid at normal room-temp, pressure isn't that much of a factor when trying to turn it into a solid... Temperatures do the trick...

(This is just me rambling, I really can't remember that much on the subject)

Best Regards :toast:

[eddieate]

I'm pretty confused with what I learned in school lol:

1. molecules in a solid state are tightly packed; molecules in a liquid state are not as tightly packed as liquids; then gas are moving pretty much freely.
2. When water freezes, it expands, same with gallium. (What happened to even more packed molecules?)
3. You can take a gas, compress it, cool it, and it'll condense into a liquid, but you can't compress a liquid into a solid.

:confused: I'm just wondering lol, someone give me an explanation.

Well as I understood its to do with the structure, you know how carbon can have lots of different forms? I.E. diamond, graphite etc. so when water freezes its takes on a solid state but the molecules are further apart because they are actually in a structure, rather than just milling around.

It looks like you can get things like solid hydrogen, I thought it was just believed to exist in the centre of gas giants like Jupiter, but according to wiki (http://en.wikipedia.org/wiki/Metallic_hydrogen#References) somebody's actually done it.
hope that helps, I may well be wrong, dont shout at me physics buffs :sofa:
Ed.

[DeltZ]

at a guess it's probably not all down to just how close molecules are together, but how they're binded. Then there's the repulsion force as your get atoms and things close and closer together...raises far steeper than exponentially. Maybe cooling make very important changes. Also there is probably a difference between atomic structure and molecular structure which affects the states and their classification.

Again, all just guessing.

[Brettbeck]

So how do you actually change liquid in to solid? Presumably it would need to be compressed somehow?

[Knight]

I'm pretty confused with what I learned in school lol:

1. molecules in a solid state are tightly packed; molecules in a liquid state are not as tightly packed as SOLIDS; then gas are moving pretty much freely.
2. When water freezes, it expands, same with gallium. (What happened to even more packed molecules?)
3. You can take a gas, compress it, cool it, and it'll condense into a liquid, but you can't compress a liquid into a solid.

:confused: I'm just wondering lol, someone give me an explanation.

Number one is true. ^^

Water will expand when it freezes because it is a bent molecule. A bent molecule is polar (strong attraction forces). Water also has two hydrogen atoms connected to a oxygen atom. This connection is called a H-FON bond. The oxygen atom will force a stronger pull on all the electrons in the molecule. This will also make it more polar. When the temperature lowers, the intermolecular forces become more dominant. This will let the positive hydrogen to create a weak bond to a negative oxygen. This creates a organized structure where as water in the liquid phase has an unorganized (tighter packs form) state.

Number three.
A solid is just a mass of molecules that have strong intermolecular forces. A gas does not have any forces because it has a very strong kinetic energy, so it is able to move freely in random lines throughout its container. So lets just focus on when a liquid becomes a solid. Pressure is only one part of the many factors that determine the ability of substances to change phases. Temperature is also very important. The lowering of the temperature will decrease the kinetic energy, and as a result the intermolecular forces will increase. A phase change will most likely happen with the changing of temperature.

[Praxis1452]

Ice is highly ordered which causes the molecules to stop from becoming too close together.

The oxygen has two lone pairs and covalently bonded to two H atoms. The two lone pairs also form a hydrogen bond to other water molecules making the h20 molecule tetrahedrally bonded to 4 hydrogens.

the lattice structure takes up a lot of empty space. I have a pic in my chem book right now that shows it heh.

[Thrilla]

#1 and #3 makes sense now, but how about gallium? It's just metal, one type of atom, that's it. And it expands quite a bit when it turns from a liquid into a solid. I can understand how molecules can affect each other with all those forces, but Ga being the same atom but not molecule, it expands :eek:

[Avman]

Gallium expands when it solidifies because it goes from an amorphous (non-structured or ordered) liquid to an ordered granular solid. The grains tend to form in an orthorhombic structure which takes up more space than the liquid form.

[serialk11r]

I'm not sure, but I think it has to do with the crystalline structure that different substances take when they turn to a solid. For example ice has a hexagonally shaped crystal. Iron has crystals in a cube I guess you could call it. Water has less volume than ice because in the liquid state the molecules can "bunch together" and fill up some of the empty space made by the hexagonal lattice structure of the ice. Gallium probably forms some type of crystal that does that. Again, I'm not sure but this is what I would imagine it to be.

[Avman]

The wiki entry on Gallium appears pretty accurate and describes and has links to diagrams of the solid crystal structure

[Praxis1452]

I'm not sure, but I think it has to do with the crystalline structure that different substances take when they turn to a solid. For example ice has a hexagonally shaped crystal. Iron has crystals in a cube I guess you could call it. Water has less volume than ice because in the liquid state the molecules can "bunch together" and fill up some of the empty space made by the hexagonal lattice structure of the ice. Gallium probably forms some type of crystal that does that. Again, I'm not sure but this is what I would imagine it to be.
density increases as temperature rises in water up to 4C. It is because you can have both phases and as you warm up the ice there are liquid molecules stuck between inside the lattice structure of the solid thereby increasing density. After 4C density again decreases.

[Vizion]

I guess the structure or the way atom arrange themselves in different states in different elements, compounds, or molecules is what make them unique from one to another. We don't know "why" it behaves this way, only know how it works, thus we call them "properties". :D

[pissboy]

I'm pretty confused with what I learned in school lol:

1. molecules in a solid state are tightly packed; molecules in a liquid state are not as tightly packed as liquids; then gas are moving pretty much freely.
2. When water freezes, it expands, same with gallium. (What happened to even more packed molecules?)
3. You can take a gas, compress it, cool it, and it'll condense into a liquid, but you can't compress a liquid into a solid.

:confused: I'm just wondering lol, someone give me an explanation.

3 isn't always correct.

Matter doesn't always have to go from gas to liquid to solid. Take carbon dioxide. Under normal circumstances, CO2 goes from solid, directly to gas in a process called sublimation. Deposition is the opposite of this. Also, don't forget the forth state of matter - plasma.