Why is CCl₄ a nonpolar molecule, but is PCl₃ a polar molecule?

Question

Accepted Answer

In this problem, we are asked true or false. Carbon tetra fluoride is a nonpolar molecule since it has no Lomb pair. While nitrogen tribromide is a polar molecule due to one lone pair to best answer this question. Let's draw the Lewis dot structure for carbon tetra fluoride and nitrogen tribromide. Beginning with carbon tetra fluoride, we make use of the need available share method. So need comes about from most things trying to acquire an octet. So in terms of carbon and fluorine, there are no exceptions to the octet rule. So we have five altogether one carbon and four fluorine. All five are trying to acquire eight valence electrons. So this is a total of 40 that we need available comes about from the valence electrons. Carbon is in group four A. So it has four valence electrons and we have four fluorine. They are in group seven A. So they have seven valence electrons. So this is a total of 32 electrons available. The difference between what we need 40 electrons and what we have available, 32 tells us that we're gonna share eight and so carbon being less electron negative than fluorine will go in the center surrounded by four fluorine. And then we're gonna share eight. So 2468, informing four bonds, we need to account for all 32 electrons available. That means we have 24 electrons left to account for each flooring needs an additional six to acquire eight and there are four of them. So six times four is 24 that will count for our remaining electrons that we have available. When we look at carbon tetra fluoride, we see that it is symmetric. When we have a symmetric molecule with the same groups attached, it will be nonpolar. Now going to nitrogen tribromide, we'll make a use of again, the need available and share method. So nitrogen and the three bromine, all four are trying to acquire an octet. So that's a total of 32 electrons that we need. The available is based on valence electrons. Nitrogen is in group five A, it has five valence electrons. We have three brom means which are group seven A. So that's seven times three plus five. So we have 26 electrons available. The difference between what we need 32 what we have available 26 says that we'll share six. So nitrogen goes in the center nitrogen, we typically form three bonds in broma, typically one. So we place nitrogen in the center and we'll form three bonds, which means we'll share six electrons. We have 20 electrons left to account for we will begin by fulfilling the octets for bromine. So each bromine needs an additional six electrons. So six times three is 18, that means then that we have two leftover to account for those remaining two go on nitrogen to fulfill its octet. And so when we look at nitrogen tribromide, we have a long pair of electrons and that long pair of electrons then makes this non symmetric a non symmetric molecule then will be polar. And so as we go back to our question, it says the carbon tetra fluoride is a nonpolar molecule since it has no lone pairs. So that is correct, that then makes it symmetric in shape. While nitrogen tribromide is a polar molecule due to one lone pair, which is correct. So that presence of that lone pair of electrons makes it non symmetric and therefore polar. So the answer to this question then is true. This corresponds with answer a thanks for watching. Hope this helped.

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Why is CCl₄ a nonpolar molecule, but is PCl₃ a polar molecule?