Most of the unique properties of water result from the fact that ...

Question

Most of the unique properties of water result from the fact that water moleculesa. are the most abundant molecules on Earth's surface.b. are held together by covalent bonds.c. are constantly in motion.d. are polar and form hydrogen bonds.

Accepted Answer

Hi everyone. Let's look at our next problem. It says the blank shape of the water molecule makes it polar and gives it the capability to act as a polar solvent. When we think about the shape of a molecule, we want to think about how many electron pairs surround the atoms and therefore what arrangement they'll make in space around the atoms. So let's think about water here and we'll start with the oxygen atoms since the hydrogen atoms just have the one pair of electrons. So they're much simpler to deal with. Oxygen in water has a full outer shell, eight pairs of electrons surrounding it. It's got two lone pairs and then two pairs shared in bonds with hydrogen. When you have four pairs of electrons surrounding an atom, we can recall that they arrange themselves in a tetra he'd rel shape and that's because the negatively charged electrons repel each other and want to be as far away from each other as possible. So having four equal angles, puts them all the maximal distance away from each other. So we'll put our hydrogen here sharing their pairs of electrons and then these remaining two legs of our tetrahedron. Our lone pairs on that oxygen. So when we look at the overall shape of the molecule, we kind of ignore the lone pairs and we end up with this kind of shape here. So we can draw that often usually drawn like this with the lone pairs like that and that makes it a polar molecule because the oxygen is much more electro negative than the hydrogen. So this part of the molecule here with the oxygen has a partially negative charge. Whereas our hydrogen have partial positive charges since the electrons spend more time away from them and near the oxygen as a result, given this arrangement in space, this whole region of the molecule as a partial negative charge. Meanwhile the region with the hydrogen is around, it has a partially positive charge. So when it interacts with other molecules, they the same way have these partial positive and partial negative reasons they're going to be attracted to that water molecule. So that gives us this polarity. So let's look at our answer choices. And this shape here that we have is choice be a bent shape. So that's our answer. B But let's look at our other answer choices to understand why they're not correct choice. A says linear, linear would be with just 180 degrees between the bonds and something like that would be if we imagine maybe a carbon atom that has a triple bond something on one side and then maybe a hydrogen on the other. We can imagine H. C. N. These pairs of electrons will be 180° apart. And this molecule has a linear shape. But you can see water is not like that. Even the water has three atoms because of the lone pairs, it takes on that bend shape. So linear might confuse us because we might be tempted to arrange them like this. But because the lone pairs are also repelling those electrons in the bond, they cause it to take on that bent shape. I see his octahedron octahedron would be you'd imagine two pyramids sort of on top of each other three dimensionally. Sorry for the not great drawing there. That would be for a molecule where your central atom has six pairs of electrons surrounding it. Uh That's what we have here are oxygen has four pairs. So it's not choice C. And finally, Choice D. Trigon all parameter. Um That would be the case if we only had um one lone pair of electrons around our oxygen and three bonds. So an example of that is the ammonia molecule where you have nitrogen with three hydrogen is around it. And they end up arranged like this and there's a lone pair. So you've got those four bonds. So you've got the um tetrahedron arrangement. But because this is a lone pair, the shape of the molecule ends up being this pyramid shape. But oxygen has two lone pairs. So you have this bent shape. So choice D. Is not our answer. So again, the choice be bent shape of the water molecule makes a polar and gets the capability to act as a polar solvent. We'll see you in the next video

Most of the unique properties of water result from the fact that water moleculesa. are the most abundant molecules on Earth's surface.b. are held together by covalent bonds.c. are constantly in motion.d. are polar and form hydrogen bonds.

Key Concepts

Polarity of Water

Hydrogen Bonding

Molecular Motion

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