Consider the following gases, all at STP: Ne, SF6, N2, CH4.
(a) W...

Question

Consider the following gases, all at STP: Ne, SF6, N2, CH4.
(a) Which gas is most likely to depart from the assumption
of the kinetic-molecular theory that says there are
no attractive or repulsive forces between molecules?

Accepted Answer

Hey everyone in this example, we need to identify the gas, which follows the notion that attractive and repulsive forces between gas molecules are negligible. We need to assume that the gasses are under similar conditions. So similar conditions would mean similar pressure, temperature and volume. So looking at our first choice, we have the noble gas, neon. We would recognize that this is just a single atom here and therefore it only has London dispersion forces which are the weakest inter molecular force. So we would go ahead and consider a as a good prospect because it, since it has such a week I. M. F. We would be able to agree with the fact that this force within this noble gas is going to be negligible among other gas molecules. So moving on to the second choice, given we have floral methane gas and we would go ahead and based on the atoms, recognize that in this molecule we do not have symmetry in our molecule. And so because there is no symmetry, we would say that therefore this is a polar molecule also contributed by the dipole created by the very electro negative slightly or partially negatively charged flooring atom, in comparison to the partially positive charge that we have on our carbon atom, which is less an electro negative. So we have a die pool created in the direction of our flooring atom. And because this is a polar molecule, for those reasons we would have the pretty strong I. M. F. Dipole dipole forces. And we cannot say that dipole dipole forces are negligible because they are quite strong. So we would go ahead and rule out Choice B because it's not a good example of a gas with negligible inter molecular forces. So moving on to choice C. We have ammonia gas and we would recognize that there's a lone pair in our LewiS structure of our nitrogen atom which we recall is located in Group five A of our periodic tables and therefore has five valence electrons. And so as we see in the formula, it's bonded to three hydrogen atoms, so it's co violently sharing three of its electrons. But we would have to complete its octet by placing a lone pair in the lewis structure. And because of not only the high higher electro negativity value for our nitrogen atom, which would give it a slightly negative charge. It also has a die pool created in the direction of its lone pair, creating this molecule or designating this molecule as a polar molecule. And so because we have this lone pair and sorry about that. So because we have this lone pair, we therefore have a polar molecule. So the lone pair creates a die pool. And because we have a polar molecule, we therefore can say we have also dipole dipole forces which are pretty strong. And so we would not use ammonia gas as a good example of a gas with the notion that the inter molecular forces of that gas are negligible. So see we rule out as well. Next we have xenon hexafluoride gas and we want to go ahead and recognize that we have this xenon atom surrounded by very six very electro negative flooring atoms which yes flooring is more electro negative than xenon being the most electro negative atom in our periodic table. And so we have di poles in the direction of all of the flooring atoms in this Lewis structure which will ultimately cancel out one another because we have a symmetrical molecule. And so because we have symmetry here, this is therefore a non polar molecule. And so we only likely have London dispersion forces which are very weak. However, we cannot consider d a good example of a gas where the inter molecular forces are negligible because this is not only a symmetrical molecule, but this is a large molecule. And that is due to the fact that when we consider our trend on our periodic table for atomic radius, which increases as we go from or towards the bottom left of our periodic tables, We would recall that Xenon is located across period six in group seven or sorry, in group eight A of our periodic tables. So around here on a periodic table and that means that it has a very large atomic radius. And so because it has a large atomic radius, this is going to make a large molecule. Not only does it have a large atomic radius for our xenon atom, but we have six flooring atoms. So this is a very large molecule which is not going to make the inter molecular forces negligible here. So we would go ahead and roll out Choice D meaning that the only good example of a gas that would have negligible inter molecular forces between the gas molecules is neon. So this will complete this example as our final answer. If you have any questions, please, lead them down below, and I will see everyone in the next practice video.

Consider the following gases, all at STP: Ne, SF6, N2, CH4. (a) Which gas is most likely to depart from the assumption of the kinetic-molecular theory that says there are no attractive or repulsive forces between molecules?

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