Water

[LJP07]

Originally Posted by hallenrm

Electronagetivity, electron pairs, tetrahedrals etc. are all secondary!

So can you give a primary reason except for the above. I believe the above can only be used to describe it in terms of it's structures etc. There is no primary reason from what I know?

[HydrogenBond]

Electronegativity is the fundamental reason for the shape of water. Oxygen is more electronegative than hydrogen. This higher electronegativity is implicit of oxygen receiving more stability by gaining extra electrons. This is due to increased magnetic addition. For example, opposite spin electrons magnetically attract inspite of charge repulsion. In the case of oxide or O-2, with the 2P orbital full, these additive pairs will also magnetically add in 3-D via the x,y,z lobes of the P-orbital. In other words, the EM force is both electrostatic and magnetic, higher electronegativity measures an atoms ability to gain magnetic attraction to compensate for the charge repulsion that will occur by gaining an extra electron. The more magnetic addition the higher the electronegativity.

In H20, the oxygen is trying to place its electrons in such as way as to maximize its magnetic addition. The hydrogen has its own agenda but does not get as much stability from magnetic addition as can oxygen. It can only mag-add via spin addition between two electrons and not in x,y,z 3-D like the P-orbital electrons around oxygen. Based on the magnetic compromise, the result is the shape we see.

If we look at hydrogen bonding it is often viewed as an electro-static bond between H and O. This is only half the story, since the oxygen is quite stable holding extra electrons (O-2) due to mag-add. The attachment of hydrogen, via the hydrogen bond, may lower the charge repulsion for oxygen, but it takes something away from its optimized mag-add, with the result the oxygen gaining potential. Left to its own devices, the oxygen will take the charge repulsion because it offers mag-stabiltiy. The hydrogen bond lowers its net staiblity.

The way the oxygen lowers its potential back is via the partial covalent nature of hydrogen bonding. This allows delocalization of the charge attracted electron density that hydrogen takes, allowing oxygen to regain some of the magnetic addition.

This battle between hydrogen and oxygen is what makes water so unique. The hydrogen is placed in a state of perpetual potential due to the higher electronegativity of oxygen. The hydrogen keeps trying to lower potential via hydrogen bonding, with the oxygen using its higher electronegativity to make this less than fully satisfying for the hydrogen.