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Utorok, 25. januára 2022
Water is a Chemical
Dátum pridania: 09.04.2002 Oznámkuj: 12345
Autor referátu: muculik
Jazyk: Angličtina Počet slov: 3 604
Referát vhodný pre: Stredná odborná škola Počet A4: 11.1
Priemerná známka: 3.00 Rýchle čítanie: 18m 30s
Pomalé čítanie: 27m 45s

Let's take another look:
[ fig of electron density map of water ]
Does this make water unusual?
YES! But it's not just that the molecule is bent that makes it special. Water is also highly polar - the two sides of water have very different charge. The lone pairs are negative - Are the Hydrogens positive?
The hydrogens are slightly positive. They get this way because of the "electronegativity" of oxygen. Electronegativity is a measure of how much one atom wants to have electrons, and oxygen wants to have electrons more than hydrogen does. Oxygen has a higher electronegativity. Because of this difference in electronegativity, the electrons in the covalent bonds between oxygen and hydrogen get pulled slightly toward the oxygen. This leaves the hydrogens a little bit electron-deficient and thus slightly positive. We can draw this polarization like this:

Or looking at it from a "net polarization" perspective, like this:

What does the polarization have to do with the properties of water?
Everything! Because water has a slightly negative end and a slightly positive end, it can interact with itself and form a highly organized 'inter-molecular' network. The positive hydrogen end of one molecule can interact favorably with the negative lone pair of another water molecule. This interaction is call "Hydrogen Bonding". It is a type of weak electrostatic attraction (positive to negative). Because each and every one of the water molecules can form four Hydrogen Bonds, an elaborate network of molecules is formed. But if the Hydrogen Bonds are weak, how can they be important?
Think of how many there are! There is strength in numbers!
The polarity also allows water interact with an electric field:

And to interact with other polar molecules - which is how substances become dissolved in water. Hydrogen + Oxygen = Water
The simple statement that water is made from hydrogen and oxygen doesn't give us a very clear picture of what really goes into the creation of a molecule of water. A quick look at the chemical equation for the formation of water tells us more. 2H2 + O2 = 2H2O
It takes two molecules of the diatomic hydrogen gas, combined with one molecule of the diatomic oxygen gas to produce two molecules of water. In other words the ratio of hydrogen to oxygen is 2:1, the ratio of hydrogen to water is 1:1, and the ratio of oxygen to water is 1:2. There's something more though that doesn't show up in the equation. Energy. The formation of water from it's elements produces, in addition to water, a tremendous amount of energy, 572 kJ to be exact.
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