Ranges of mp and bp

[|ll|lll|]

Water is a polar, covalent molecule that has a melting point and boiling point of 0 degrees and 100 C.
This is considered relatively high in comparison to other polar molecules which have hydrogen bonding between them, like NH3 and HF.
However, water has the highest bp and mp due to the tetrahedral (?) structure it has when it is in solid, and these kind of structures require the most amount of energy to break apart.

I was just wondering, why does water have one of the largest range of mp and bp (besides comparing to carbon compound)?
Has this got to do with the structure they are arranged in or the type of intermolecular forces?

Cheers

[Keo]

Water has a high boiling point which is due to its extensive hydrogen bonding between it's molecules. So it's more like the intermolecular forces between the water, someone correct if I am wrong though.

I see you have a question mark next to tetrahedral so ill explain. It has a tetrahedral structure which looks like this http://www.chembase.com/gallery/962/3D_model_hydrogen_bonds_in_water.jpg
red being the oxygen and white being the hydrogen, hence where it gets its name H2O.

Tetrahedral basically means triangular pyramid, which you can see from the picture how water is basically structured.

Hope I helped

[REBORN]

AFAIK Water is angular/bent/V-shape. Tetrahedral is something like Methane.

[b^3]

Its the tetrahedral arrangement of the molecules not of the molecule itself. In liquid form each moleculen forms on aveage 2 hydrogen bonds (not 100%) but these are constanlty changing between different molecules. In solid form, i.e. ice, each molecule forms 4 hydrogen bonds and has the tetrahedral structure above.

[|ll|lll|]

Yeah, I recently found out that it wasn't exactly tetrahedral, but hexagonal.
Which of the two terms are more accurate?

Also, I think the range of the mp and bp of water has a relationship with the amount of energy it needs to change from one state to another. For example, a certain amount of energy is needed for water to change from solid --> liquid, and even more energy is required from liquid --> gas.
I don't understand why however.

Has this got anything to do with surface energy too? (Highly doubt so, but might still make sense somehow...)

[Mao]

Yeah, I recently found out that it wasn't exactly tetrahedral, but hexagonal.
Which of the two terms are more accurate?

Also, I think the range of the mp and bp of water has a relationship with the amount of energy it needs to change from one state to another. For example, a certain amount of energy is needed for water to change from solid --> liquid, and even more energy is required from liquid --> gas.
I don't understand why however.

Has this got anything to do with surface energy too? (Highly doubt so, but might still make sense somehow...)

OH bonds form a six-membered hexagonal ring in ice. But as far as each atom is concerned, you'll find they're all connected to other atoms in a tetrahedral arrangement. (E.g. an O atom is bonded to two H atoms, and H-bonds to two other H atoms).

When ice melts to water,  molecules in ice (rigid structure) become disordered, thus some bonds are broken (therefore requires energy).

Surface energy is a different application of the concept of intermolecular bonding.

[b^3]

So I'm guessing that we are putting down the wide range over the mp and bp down to the fact that the hydrogen bonds between molecules arrange themselves in specific ways and structure depending on the state that it is in?

[Mao]

What are we talking about here?
The fact that water has a high MP and BP compared to other compounds.
Or the fact that the MP to BP range for water is higher than other compounds?

[b^3]

I read it as the large diff between mp and bp but |ll|lll| did ask the question so.

[Mao]

that's largely got to do with the nature of hydrogen bonding.

The theory is quite complex, but it basically comes down to hydrogen bonding being very strong in water.

[|ll|lll|]

^ Can you explain, Mao?

Is hydrogen bonding the strongest in water?

[Mao]

Water has two hydrogen (positive sites) and two lone pairs (negative sites). This means hydrogen bonding in water can form very complex networks, thus promising raising the internal energy of liquid.

Ammonia has three hydrogen and one lone pair, whilst it can h-bond, it cannot form a large network. Hydrogen fluoride is similar.

a lot of current research is going into the nature of hydrogen bonding. We don't actually know why it is so strong yet.

[Mao]

Water has two hydrogen (positive sites) and two lone pairs (negative sites). This means hydrogen bonding in water can form very complex networks, thus promising raising the internal energy of liquid.

And hence high specific heat capacity for water?

Heat capacity is a fairly advanced thermodynamics quantity, a proper interpretation involves a property that is not taught in VCE (i.e. entropy).

For the sake of VCE, you can think of hydrogen-bonds as bonds between molecules, which may absorb energy. Thus a liquid with more H-bonds will be able to absorb more energy.

[stonecold]

Can I say that the areas under these curves are all equal?

Yes.

[Mao]

The area under the graph in fact are all equal to 1.