Why do some polar molecules that have symettery have no over overall net polarity? e.g. CCl4 not H20?

Answer 1

It has to do with the electronegativities of the elements as well as the shape of the molecule.

In H2O for example, the bond angle between the hydrogen molecules is less than 180 degress, so you have the hydrogen sticking out from one end and the oxygen sticks out the other end. This is why the molecule is polar, because the oxygen has a much lower electronegativity than the hydrogens, so at any given time, more electrons are by the oxygen.

With the Carbontetrachloride, the molecule looks sort of like a tripod, you have the carbon in the middle and the four chlorines sticking out from it, three going down in the shape of a tripod and one sticking up from the other side, because of this the molecule is not polar

Answer 2

Because although they are polar, they are surrounded by equally polar molecules that basically 'block' any polarity from the outside.

H20 has a very negative oxygen sticking out on one side while the two positive hydrogens stick out on the other side, making it like a bar magnet.

CCl4 is tetrahedral which means it is completely surrounded by chlorine. And chlorine isn't negative or positive compared to other chlorine. And, since the molecule is sp3 hybridized, all the chlorine molecules have an equal orbital shape...so one chlorine isn't being pulled closer than others..causing complete symmetry and no net polarity.

Answer 3

For a molecule to be polar, it must fulfill 2 criteria

1. it must have at least one polar covalent bond
2. it must have the correct geometry

Water fulfills both criteria, carbon tetrachloride only the first one.

Answer 4

CCl4 is not a particularly polar compound, so your question doesn't make sense.

Answer 5

because when it freezes the molecules are joined by other molecules from the cold air.

Answer 6

Think you should learn to spell correctly first!