[chstudent24]

What types of intermolecular force is (are) common to a) Xe and methanol (CH3OH), b) CH3OH and acetonitrile (CH3CN), c) NH3 and HF?

XE-CH3OH

London-molecule isn't non polar so can't be
Dipole-Dipole-moleclue is polar so dipole-dipole
Hydrogen-no N, O, F or C on the left so can't be
Ionic- Can't be because this isnt between a metal and nonmetal


CH3OH-CH3CN

London-the EN is very close i want to say this is a london
Dipole-Dipole-EN come close , the math would say its a close polar molecule so i'd say Dipole-Dipole
Hydrogen-I see H bonded to O and C but not sure if i'm making a mistake here to label this a hydrogen bond
Ionic- Can't be because this isn't between a metal and nonmetal



NH3-HF

London-isn't polar so can't be
Dipole-Dipole-is polar so does have this but hydrogen since of very high polarity
Hydrogen- H is bonded to an N and F so i'd assume this is a hydrogen bond
Ionic- Can't be because this isn't between a metal and nonmetal



not exactly sure if the question was asking which do they all have in common jointly, if it was I would say Dipole-Dipole from what i wrote above. Please correct any flaws with my reasoning!

[chstudent24]

the next question is

Which member of the following pairs has the stronger intermolecular dispersion forces

a) Br2 or O2


b) CH3CH2SH or CH3CH2CH2CH2SH


c) CH3CH2CH2CL or (CH3)2 CHCL


I'm a bit confused on the wording of the question. Is it asking  Molecule A vs Molecule B which has the stronger forces for each letter?

[chstudent24]

What types of intermolecular force is (are) common to a) Xe and methanol (CH3OH), b) CH3OH and acetonitrile (CH3CN), c) NH3 and HF?

XE-CH3OH

London-molecule isn't non polar so can't be
Dipole-Dipole-moleclue is polar so dipole-dipole
Hydrogen-no N, O, F or C on the left so can't be
Ionic- Can't be because this isnt between a metal and nonmetal


CH3OH-CH3CN

London-the EN is very close i want to say this is a london
Dipole-Dipole-EN come close , the math would say its a close polar molecule so i'd say Dipole-Dipole
Hydrogen-I see H bonded to O and C but not sure if i'm making a mistake here to label this a hydrogen bond
Ionic- Can't be because this isn't between a metal and nonmetal



NH3-HF

London-isn't polar so can't be
Dipole-Dipole-is polar so does have this but hydrogen since of very high polarity
Hydrogen- H is bonded to an N and F so i'd assume this is a hydrogen bond
Ionic- Can't be because this isn't between a metal and nonmetal



not exactly sure if the question was asking which do they all have in common jointly, if it was I would say Dipole-Dipole from what i wrote above. Please correct any flaws with my reasoning!

hey everyone still wanting to double check my work here please let me know if my logic is off!!!

[chstudent24]

the next question is

Which member of the following pairs has the stronger intermolecular dispersion forces

a) Br2 159.8gmol or O2 32gmol

therefore Br2 has stronger intermolecular dispersion forces



b) CH3CH2SH 62.15gmol or CH3CH2CH2CH2SH 90.21gmol

therefore CH3CH2CH2CH2SH has stronger intermolecular dispersion forces



c) CH3CH2CH2CL 78.55 or (CH3)2 CHCL 78.55

both have the same weight but i think CH3CH2CH2CL is stronger because it has less branches in the structure?

hey please double check my answers

[MrTeo]

I'll try to help you... first of all i don't understand why you say:

London-molecule isn't non polar so can't be
Ionic- Can't be because this isnt between a metal and nonmetal

London forces are intermolecular forces between induced dipoles (this happens e.g. because of the dynamic state of the electron cloud) and they don't depend on the dipolar nature of the molecule considered. Think only at the fact that they're the only (very low, usually about 1 kJ/mol) attractions which keep together noble gases in their liquid form. So these interactions are more or less always present... the matter is if they are relevant or not, so if you need to keep track of them when you work on a quantitative analysis of the phenomenon (sometimes you have too: consider how the additional pressure in the van der Waals equation is evaluated from the effect of this kind of bonds).

Then, ionic forces are not only the ones you know in the NaCl crystal so you can't simply say that you need a metal and a non-metal to form such bonds. Most of the times happens so but think only at the intercation between dipoles and ions or induced dipole and ions. That's why salt solvates in water and that's also why water is such a good solvent for ionic and polar compounds.

So, let's check your answers:

Xe - CH₃OH

Obviously London forces and also van der Waals forces (in the form of interaction between a dipole, CH₃OH, and an induced dipole, Xe)

CH₃OH - CH₃CN

London (here i would say they're irrelevant), not very strong dipole-dipole attraction as CH₃CN isn't very polar and I'd say hydrogen bond too with O and N (the hydrogen bond of the oxydrile with N seems the strongest also because H has its electron cloud decentralized while the other bonds are almost homopolar with C)

NH₃ - HF

London (irrelevant again), a strong hydrogen bond (because of the highest electronegativity of the periodic table, 4.0 of fluorine and the nitrogen which polarizes the H of ammonia) an dipole-dipole forces.

Moreover consider that a dipole-dipole bond is also strengthened by the dipole-induced dipole bond that forms because of the electromagnetic interaction, so aswering to your questions I'd say they have in common London forces and dipole-induced dipole interactions.

I'll post something later on the second question but first tell me if this answer is ok or if you need any more help with these phenomena... 

[kd.gns]

hmm, when I saw this question, I understood it to be asking you to find the common intermolecular forces between a pure sample of compound A, and a pure sample of compound B, so for Xe/CH₃OH only London forces are common, since pure Xe would not exhibit induced dipole interactions. I could be wrong though, it could be asking what are the intermolecular forces in a mixture of the two compounds given, in which case a dipole-induced dipole should be the correct answer for Xe/CH₃OH

[chstudent24]

I'll try to help you... first of all i don't understand why you say:

London-molecule isn't non polar so can't be
Ionic- Can't be because this isnt between a metal and nonmetal

London forces are intermolecular forces between induced dipoles (this happens e.g. because of the dynamic state of the electron cloud) and they don't depend on the dipolar nature of the molecule considered. Think only at the fact that they're the only (very low, usually about 1 kJ/mol) attractions which keep together noble gases in their liquid form. So these interactions are more or less always present... the matter is if they are relevant or not, so if you need to keep track of them when you work on a quantitative analysis of the phenomenon (sometimes you have too: consider how the additional pressure in the van der Waals equation is evaluated from the effect of this kind of bonds).

Then, ionic forces are not only the ones you know in the NaCl crystal so you can't simply say that you need a metal and a non-metal to form such bonds. Most of the times happens so but think only at the intercation between dipoles and ions or induced dipole and ions. That's why salt solvates in water and that's also why water is such a good solvent for ionic and polar compounds.

So, let's check your answers:

Xe - CH₃OH

Obviously London forces and also van der Waals forces (in the form of interaction between a dipole, CH₃OH, and an induced dipole, Xe)

CH₃OH - CH₃CN

London (here i would say they're irrelevant), not very strong dipole-dipole attraction as CH₃CN isn't very polar and I'd say hydrogen bond too with O and N (the hydrogen bond of the oxydrile with N seems the strongest also because H has its electron cloud decentralized while the other bonds are almost homopolar with C)

NH₃ - HF

London (irrelevant again), a strong hydrogen bond (because of the highest electronegativity of the periodic table, 4.0 of fluorine and the nitrogen which polarizes the H of ammonia) an dipole-dipole forces.

Moreover consider that a dipole-dipole bond is also strengthened by the dipole-induced dipole bond that forms because of the electromagnetic interaction, so aswering to your questions I'd say they have in common London forces and dipole-induced dipole interactions.

I'll post something later on the second question but first tell me if this answer is ok or if you need any more help with these phenomena... 

Hey thank you so much for your reply, you really explain things well. Chemistry has always been a tough subject for me so I have to read things over and over and think about them to make them click. I'm a visual learner so when i read about bonds and different forces and stuff I get confused if i can't visualize whats going on.

In terms of not understanding why I said

London-molecule isn't non polar so can't be
Ionic- Can't be because this isnt between a metal and nonmetal

Its just me putting my current understanding of something out in the open so life savers like you can see where I'm messing up and get me back on track
Again thank you so much for your time and help.

[MrTeo]

Again thank you so much for your time and help.

Not at all 

Anyway looks like there's still some work to do with those intermolecular forces...
Talking of dispersion forces makes me think at London forces and as regards your question I think that what matters most is to find out the molecules which have the strongest attraction between them. Molecule dimensions are really important to evaluate the strongness of these forces as a "bigger" compund increases polarization effects.

1) Br₂ has stronger forces than O₂ (OK)

2) CH₃CH₂CH₂CH₂SH has stronger forces than CH₃CH₂SH (OK)

3) About this I'm not so sure... they've got the same weight so we'll have to check their structure:



(Hope there are no mistakes in these, as I'm not really into organic chemistry...  )

Anyway they've got more or less the same structure... I'd say the 2nd one is the strongest beacuse of the asymmetrical chlorine which polarizes charge on itself (a ) even if this isn't really a London interaction while seems more a dipolar one.

Better posting this last one on the organic forum... or wait for someone who knows the answer 

[Astrokel]

Surface area to exert intermolecular attraction - Branching effect

So MrTeo is correct, 1-chloropropane will have stronger intermolecular forces than 2-chloropropane.