Oxygen has a slightly negative charge, while the two hydrogens have a slightly positive charge. This is why you can fill a glass of water just barely above the rim without it spilling.īecause of water's polarity, it is able to dissolve or dissociate many particles. Water molecules are very cohesive because of the molecule's polarity. Cohesion is intermolecular forces between like molecules this is why water molecules are able to hold themselves together in a drop.Liquids with stronger intermolecular interactions are usually more viscous than liquids with weak intermolecular interactions. We normally think of liquids like honey or motor oil being viscous, but when compared to other substances with like structures, water is viscous. Viscosity is the property of fluid having high resistance to flow.Water has very strong intermolecular forces, hence the low vapor pressure, but it's even lower compared to larger molecules with low vapor pressures. Vapor pressure is inversely related to intermolecular forces, so those with stronger intermolecular forces have a lower vapor pressure. Water's heat of vaporization is 41 kJ/mol. Vaporization occurs when a liquid changes to a gas, which makes it an endothermic reaction. Water also has an exceptionally high heat of vaporization. Water's high surface tension is due to the hydrogen bonding in water molecules. Surface Tension, Heat of Vaporization, and Vapor Pressureīesides mercury, water has the highest surface tension for all liquids. This is also why sweat is able to cool our bodies. If water was very easy to freeze or boil, drastic changes in the environment and so in oceans or lakes would cause all the organisms living in water to die. The boiling and freezing points of water enable the molecules to be very slow to boil or freeze, this is important to the ecosystems living in water. The same concept is applied to freezing point as well, as seen in the table below. This is because water requires more energy to break its hydrogen bonds before it can then begin to boil. So despite its small molecular weight, water has an incredibly big boiling point. And we all know that the boiling point of water is 100☌. One more up and you find that H 2S (hydrogen sulfide) has a boiling point at -62☌. Moving up, the next hydride would be H 2Se (hydrogen selenide) with a boiling point of -42☌. So the hydride for tellurium: H 2Te (hydrogen telluride) has a boiling point of -4☌. If you look at the periodic table and locate tellurium (atomic number: 52), you find that the boiling points of hydrides decrease as molecule size decreases.
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