Shape of Molecule

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Alison Trinh 1E
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Joined: Thu Jul 25, 2019 12:16 am

Shape of Molecule

Postby Alison Trinh 1E » Fri Nov 08, 2019 2:34 pm

Just to clarify, differences in characteristics such as boiling point of two different molecules that have the same molecular formula can be attributed to their different shapes?

Shannon Asay 1C
Posts: 102
Joined: Fri Aug 09, 2019 12:16 am

Re: Shape of Molecule

Postby Shannon Asay 1C » Fri Nov 08, 2019 2:45 pm

Yes, that's correct. For example, two molecules, like pentane and 2,2-Dimethylpropane, both have the molecular formula C5H12. They have the same number of electrons, so their shape influences the strength of attraction. Certain shapes allow the molecules to get closer so they can have stronger induced dipole-induced dipole interactions, and stronger intermolecular forces means higher boiling and melting points.

Jordan Ziegler 2J
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Joined: Sat Aug 17, 2019 12:15 am

Re: Shape of Molecule

Postby Jordan Ziegler 2J » Fri Nov 08, 2019 3:06 pm

To add on:

When two oblong polar molecules have induced-dipole induced-dipole attraction, the distance between the two dipoles is much shorter in comparison to the attraction between two spherical molecules.

This allows longer polar molecules to orient themselves such that they align and have strong interaction.

Posts: 50
Joined: Thu Jul 25, 2019 12:17 am

Re: Shape of Molecule

Postby nickianel_4b » Fri Nov 08, 2019 7:05 pm

Yes, for example, as Dr. Lavelle said in lecture: instantaneous dipoles in two rod-shaped molecules are closer, so therefore stronger than in two spherical molecules. This means that rod-shaped molecules would require more energy to break apart (like when boiling) than with spherical molecules.

Sally Qiu 2E
Posts: 105
Joined: Fri Aug 30, 2019 12:18 am

Re: Shape of Molecule

Postby Sally Qiu 2E » Fri Nov 08, 2019 7:21 pm

yes; shape can determine how close molecules are able to get to each other.

Alice Chang 2H
Posts: 101
Joined: Fri Aug 30, 2019 12:18 am

Re: Shape of Molecule

Postby Alice Chang 2H » Fri Nov 08, 2019 8:11 pm

Yes, shape affects the strength of the interaction.

This sounds like a dumb comparison, but the way that I saw it was if I had 2 sets of magnets:
- 1 set is two flat bar magnets
- 1 set is two sphere magnets like marbles
If I played around with these magnets, it would be much more difficult to separate the bar magnets than the sphere magnets because there is no space to push my fingers through the bar magnets if they're stacked on top of each other on the flat side. Meanwhile, for the sphere magnets, I can easily pull these apart because I can grasp my hands around them and separate them with my fingers.

Hope this visual helps? LOL

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