In each pair of compounds, pick the one with the higher vapor pressure at a given temperature. Explain your reasoning. c. CH₃OH or H₂CO

Video transcript

hey everyone in this example, we need to identify which compound carbon dioxide or sulfur dioxide has the higher vapor pressure. So we should recall that the stronger the inter molecular forces that are present that will correspond to a lower value for vapor pressure. So we need to determine which of our given molecules has the weaker inter molecular forces present. So first looking at carbon dioxide, we recognize that carbon dioxide consists of a central carbon atom surrounded by two oxygen atoms where carbons bonding preferences to have four bonds. So we would have to double bonds in this molecule and then our lone pairs on oxygen, which would have two sets of lone pairs since it has a total of six valence electrons because oxygen is in group six A. So this is our molecule for C. 02. And although we recognize that our oxygen atoms in this molecule have a partially negative charge with high poles in the direction of oxygen, based on oxygen being the more electro negative atom in this molecule. Because we recall that our electro negativity trend increases As we go towards the top right of our periodic tables, we would see that these two disciples are going to cancel and they cancel because we have symmetry in this molecule being the two oxygen atoms that have these disciples. And so because these disciples canceled, you can say therefore this is a non polar molecule. Sorry about that. So this is a non polar molecule. So the only force present is going to be our London dispersion force which we would recognize as one of our weaker inter molecular forces. Now we want to compare this to silver dioxide, which we recognize consists of a single sulfur atom, where we would recall that since sulfur has six valence electrons because it's in Group six A it's going to have to double bonds to oxygen in this molecule. And because sulfur is in period three of our periodic tables, it can have an expanded octet, meaning we would fill in the rest of its valence electrons as a set of lone pairs at the top of our molecule, which is why we have this bent shape in our molecule. We also want to fill in the two lone pairs for oxygen atoms and this would complete our molecule for sulfur dioxide. So right now we would recognize that oxygen is more electro negative than sulfur, based on our electro negativity trend that we would recall. However, we also have a slightly negative charge contributing from the dye pole that is forming in the direction of our lone pair here, at the top of our sulfur atom. So we have three die poles occurring in this molecule. But because we have a symmetry coming from the lone pair on our sulfur atom, the dye polls do not cancel. And so we would say that therefore this is going to be a polar molecule where we would now recognize that we should have the dipole dipole inter molecular force, which we would recognize as our or as a stronger inter molecular force in comparison to our London dispersion forces. So based on what we've outlined, we can conclude this example by saying therefore carbon dioxide has the weaker inter molecular force present, which we stated was London dispersion force, and so thus it will have a higher vapor pressure. And so this explanation here will be our final answer to complete this example. So I hope that everything I reviewed was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video.