Bonding and Intermolecular Forces Content Review Video

Post Reply
mcat5122018
Posts: 17
Joined: Sat Mar 03, 2018 3:33 pm

Bonding and Intermolecular Forces Content Review Video

Post by mcat5122018 » Mon Mar 12, 2018 7:27 pm

Hi,

I was watching this particular content review video and one statement made during the video was that we cannot predict relative melting or boiling points because they depend on intermolecular attractions while discussing covalent bonds. I am a bit confused by this statement. The way I understood this is that for ionic and covalent bonds we can predict melting and boiling points, but not for intermolecular attractions, such as H bonding, dipoles, etc. Is this correct?

Thanks.
NS_Tutor_Andrew
Posts: 520
Joined: Mon May 23, 2016 1:47 pm

Re: Bonding and Intermolecular Forces Content Review Video

Post by NS_Tutor_Andrew » Wed Mar 14, 2018 12:45 pm

Hi mcat5122018,

Great question! Let me clarify...the idea is basically that you can look at an ionic compound and say "wow, that compound must have high melting/boiling points because of that ionic bonding," but you can't do something similar with covalent bonds. Covalently bonded compounds can have low melting/boiling points or high melting/boiling points, as determined by a combination of molecular weight and intermolecular forces. For covalent compounds, high molecular weights and strong intermolecular forces will increase the melting/boiling points.

Hope this makes sense! If not, let me know -- this is an important idea to get the hang of :).
Andrew D.
Content Manager, Next Step Test Prep.
mcat5122018
Posts: 17
Joined: Sat Mar 03, 2018 3:33 pm

Re: Bonding and Intermolecular Forces Content Review Video

Post by mcat5122018 » Wed Mar 14, 2018 6:07 pm

Hi Andrew,

Just so I understood is correctly, both ionic and covalent bonds are considered intramolecular forces, but what makes it hard to predict boiling and melting points in covalent bonds has to do with intermolecular forces at play as well as their molecular weight?

Thanks for your help!
NS_Tutor_Andrew
Posts: 520
Joined: Mon May 23, 2016 1:47 pm

Re: Bonding and Intermolecular Forces Content Review Video

Post by NS_Tutor_Andrew » Thu Mar 15, 2018 4:05 pm

Yes, that sounds right! I would go even further: for covalent compounds, the only relevant factors for predicting MP/BP are molecular weight and intERmolecular forces like H-bonding, dipoles, etc.

(Actually, there's a third factor -- stacking can also be important, with good stacking being associated with a higher MP. This is especially relevant for saturated vs. unsaturated fats. However, you can view that as a special case of inTERmolecular forces, because good stacking means that the molecules experience intermolecular forces more effectively.)
Andrew D.
Content Manager, Next Step Test Prep.
mcat5122018
Posts: 17
Joined: Sat Mar 03, 2018 3:33 pm

Re: Bonding and Intermolecular Forces Content Review Video

Post by mcat5122018 » Fri Mar 16, 2018 1:54 am

Thank you for that clarification. Now, it all makes sense. :D
NS_Tutor_Andrew
Posts: 520
Joined: Mon May 23, 2016 1:47 pm

Re: Bonding and Intermolecular Forces Content Review Video

Post by NS_Tutor_Andrew » Fri Mar 16, 2018 3:47 pm

Excellent, very glad to help!!
Andrew D.
Content Manager, Next Step Test Prep.
Post Reply