North. You can't mix inter and intramolecular forces. A covalent bond between 2 hydrogens and 1 oxygen makes water. A change in physical state does not change the chemical state. Each bond requires a discreet energy amount to break a covalent bond. Each bond has a bond length and a bond strength. On average for an H-O single bond (like the two in a water molecule) that energy is 450 KJ/mol. Meaning you have to pump that much energy into the molecule. After that, water does not exist, only hydrogen and oxygen molecule. The electolysis of water is an example of a chemical change.
When water is boiled the molecules vibrate around so that the relatively weak hydrogen bonds no longer orient to keep the molecules in the liquid state. Each molecule can then escape as a gas molecule since it no longer feels the intermolecular attraction of its neighbors. The molecule still has the same geometry however. The bond angle remains 104.5 degrees. The reason water has all of these properties is due to its geometry.
From MadSci Network.
Consider the water molecule as it actually is. The bonds between oxygen and hydrogen are quite polar. Oxygen holds electrons more strongly than hydrogen does, and so the oxygen atom accumulates a negative electrical charge, while the hydrogens have a positive charge.
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Because the molecule is bent, the hydrogens are both on the same side of the oxygen atom. This results in one side of every water molecule having a permanent positive charge, and the other side having a permanent negative charge; such a situation is called a permanent dipole. Since opposite charges attract, water molecules are strongly attracted to each other and to other polar molecules (molecules having permanent dipoles).
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Because the charge separation (or dipole) is so strong in water, it is able to induce temporary dipoles even in non-polar molecules. The result is that water is the "universal solvent." Almost anything will dissolve in water, even if only to a very small extent. Thus, water is able to bring together a wide variety of substances, which appears to be a prerequisite for life.
Water molecules attract each other strongly (but not too strongly), and so water is a liquid over a wide range of temperatures and pressures. This is important if you want to have liquid solutions of anything...
Even water's high surface tension (the tendency to bead up, rather than spread out the way alcohol or gasoline does) helps it be uniquely suited for supporting life -- and water would not have so much surface tension if it were not such a polar molecule.
Now, if water were linear the O-H bonds would still be polar -- they would each have a positive and a negative end -- but because they point in opposite directions the molecule as a whole would be completely non-polar.
To understand the consequences of this, consider the similar (but much more massive) molecule carbon dioxide (CO2).
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Unlike water, carbon dioxide is extremely reluctant to liquify. CO2 cannot be liquified at any temperature, if the external pressure is lower than 4.1 atmospheres. The temperature range in which CO2 remains liquid, even at that rather high pressure, is not large.
Furthermore, CO2 is completely non-polar and so is not able to dissolve very many other substances.
So if water were linear rather than bent,
it would not liquify except at quite high pressures, and it would probably not remain liquid over more than about a 20° C. temperature range at best.
it would dissolve very few other substances.
Hope this helps,
Mark Vitrone
