Thread: Why is water bipolar?

It has been awhile since chemistry class, and I am not even sure if they mentioned it at all.

Are either oxygen or hydrogen naturally charged? or does the bonding of them create the charge differentiation?

The bond angle is only 109 degrees (approx). Consequently you have a slightly electronegative end to the molecule and a slightly electropositive end. This is responsible for a host of the peculiar properties of water.

However, I have absolutely no idea as to why the bond angle is not 180 degrees.

Why is water bipolar?

sorry ... shouldn't laugh at water's misfortune ...
perhaps treatment would help?

to avoid this sort of confusion, water is generally called "a polar molecule"
(and, in case it comes up in any discussions, the Earth's magnetic structure is called a "dipole") -
bipolar ... best left for medical crowd ...


Prof Jill Granger provides a simple answer -

Why does the water molecule look bent?

The water molecule maintains a bent shape (bent at 107.5 degrees** actually) because of two considerations. First the tetrahedral arrangment around the oxygen and Second the presence of lone pair electrons on the oxygen.

What are Lone Pair Electrons?

These are the electrons that are not involved in the covalent bonds. The pairs of electrons are left alone. In our picture they are represented by the double dots. These lone pairs are very negative - containing two negative electrons each - and want to stay away from each other as much as possible. These repulsive forces act to push the hydrogens closer together

- Professor Jill Granger, The Chemistry of Water; Structure Means Function / http://witcombe.sbc.edu/water/chemistrystructure.html

**I've noted that 109.5 deg turns up in other literature, so one may be a missed typo? ... I'm not alert enough to do the math ...

Originally Posted by Cold Fusion

Are either oxygen or hydrogen naturally charged? or does the bonding of them create the charge differentiation?

Elements as such do not have a charge.

Hydrogen's* Nucleus is just a proton, Oxygen has a more massive nucleus which attracts the bonding electrons more. In a polar covalent bond, the electrons are shared between H and O. The electrons are closer to the atom with higher electronegativity (more massive nucleus in same period), in this case O. This means O has a negative charge and H has a positive charge in the molecule.

*Discounting isotopes - Deuterium, Tritium.

actually the unbonded pair of electrons on the oxygen repell the eelectrons on the hydrogens causing the bent configuration.

..
H--O--H the Hs should be bent down (have no way to draw it correctly)

Originally Posted by fizzlooney

actually the unbonded pair of electrons on the oxygen repell the eelectrons on the hydrogens causing the bent configuration.

..
H--O--H the Hs should be bent down (have no way to draw it correctly)

Like that?

Interesting....so....physical position of the electrons within the molecule effects charge distribution? For some reason I thought that the electrons added to a central magnetism of the atom or molecule as a whole.

"First the tetrahedral arrangment around the oxygen and Second the presence of lone pair electrons on the oxygen. "

Very interesting about the tetrahedral thing...thanks for bringing that up.

Originally Posted by fizzlooney

actually the unbonded pair of electrons on the oxygen repell the eelectrons on the hydrogens causing the bent configuration.

..
H--O--H the Hs should be bent down (have no way to draw it correctly)

Not really. In a water molecule each hydrogen forms a sigma bond between the hydrogen's 1s orbital and the oxygen's p orbitals. Since the oxygen's p orbitals lay 90 degrees from each other, this would result in a molecule with a bond angle of 90 degrees. But oxygen is too small for the hydrogens to be 90 degrees from each other, because they would bump up against each other, so the bond angle is bent enough to give the hydrogens the room that they need. So if you want to try to boil it down to one single factor, it's repulsion between the hydrogens that causes the bent bond angle, not repulsion between electrons.

I think I used to know that. It occurs to me, in a rather sad, introspective way, that if I could actually remember everything I knew at one time I would be ****ing awesome. 8)

I think I used to know that. It occurs to me, in a rather sad, introspective way, that if I could actually remember everything I knew at one time I would be ****ing awesome.

Lol; make a massive notepad like I did then!!! It is 60 pages and counting!

Originally Posted by Ophiolite

I think I used to know that. It occurs to me, in a rather sad, introspective way, that if I could actually remember everything I knew at one time I would be ****ing awesome. 8)

that's the downside of "forgotten more than most people learn ..."

And I rest my case:::
molecule is an aggregation of atomic nuclei and electrons that is sufficiently stable to possess observable properties— and there are few molecules that are more stable and difficult to decompose than H2O. In water, each hydrogen nucleus is bound to the central oxygen atom by a pair of electrons that are shared between them; chemists call this shared electron pair a covalent chemical bond. In H2O, only two of the six outer-shell electrons of oxygen are used for this purpose, leaving four electrons which are organized into two non-bonding pairs. The four electron pairs surrounding the oxygen tend to arrange themselves as far from each other as possible in order to minimize repulsions between these clouds of negative charge. This would ordinarly result in a tetrahedral geometry in which the angle between electron pairs (and therefore the H-O-H bond angle) is 109.5°. However, because the two non-bonding pairs remain closer to the oxygen atom, these exert a stronger repulsion against the two covalent bonding pairs, effectively pushing the two hydrogen atoms closer together. The result is a distorted tetrahedral arrangement in which the H—O—H angle is 104.5°.

I think you are mistaken scifor, the hydrogen atoms are closer than they would be if 90' from eachother, showing that there is plenty of "room" for them to be 90' from eachother, no?

Originally Posted by fizzlooney

In H2O, only two of the six outer-shell electrons of oxygen are used for this purpose, leaving four electrons which are organized into two non-bonding pairs. The four electron pairs surrounding the oxygen tend to arrange themselves as far from each other as possible in order to minimize repulsions between these clouds of negative charge. This would ordinarly result in a tetrahedral geometry in which the angle between electron pairs (and therefore the H-O-H bond angle) is 109.5°. However, because the two non-bonding pairs remain closer to the oxygen atom, these exert a stronger repulsion against the two covalent bonding pairs, effectively pushing the two hydrogen atoms closer together. The result is a distorted tetrahedral arrangement in which the H—O—H angle is 104.5°.

This is a description of water that's commonly found in low-level chemistry textbooks, but unfortunately it's not really accurate. Sadly, it is indeed what a great many undergrads taking Chem 101 learn though...

Originally Posted by marcusclayman

I think you are mistaken scifor, the hydrogen atoms are closer than they would be if 90' from eachother, showing that there is plenty of "room" for them to be 90' from eachother, no?

No, they would be much closer together if they were 90 degrees apart rather than the 105 or so that they are.

But the good news is there is medication for all the bipolar folks here.

I'll trust you scifor, i guess I don't know my angles very well.