Molecular shape

(Polar molecules, Non-polar molecules, etc.)

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Emma Scholes 1L
Posts: 62
Joined: Fri Sep 28, 2018 12:18 am

Molecular shape

Postby Emma Scholes 1L » Thu Nov 15, 2018 11:43 am

How does the molecular shape affect the boiling point?

Germar G 4F
Posts: 38
Joined: Fri Sep 28, 2018 12:28 am

Re: Molecular shape

Postby Germar G 4F » Thu Nov 15, 2018 11:53 am

The shape of a molecule directly influences the strength of interactions by attractive/repulsive forces. Dr. Lavelle used the rod-shaped vs. spherical shape example in lecture, where the rod-shaped molecules have a stronger bond/higher boiling point because the dipole-dipole attractions were closer to each other. Since the molecule shape affects the strength of interactions, this means boiling point is also related to the molecule shape.

Madelyn Romberg 1H
Posts: 102
Joined: Tue Oct 02, 2018 12:16 am

Re: Molecular shape

Postby Madelyn Romberg 1H » Thu Nov 15, 2018 11:56 am

A good thing to think about are organic molecules (hydrocarbons, more specifically, alkanes). Van Der Waals forces are a strong contributor to the boiling point of molecules. Longer, more linear alkanes have a stronger Van Der Waals forces and therefore it requires more energy to break this attraction (meaning a higher boiling point). However, when adding side chains, it can interrupt Van Der Waals forces (some branching does contribute to a spherical shape as talked in the previous post), and therefore it requires less energy to break these bonds, meaning a lower boiling point.

Sofia Ban
Posts: 80
Joined: Fri Sep 28, 2018 12:25 am

Re: Molecular shape

Postby Sofia Ban » Thu Nov 15, 2018 11:58 am

The relative strength of the intermolecular forces helps determine the boiling points. Stronger intermolecular bonds require more energy to break, so substances with stronger bonds will have a higher boiling point.(vice versa) Furthermore, more branched particles have LESS surface area compared to a straight chain molecule, hence experience less Van der Walls forces, lowering their boiling points. (Van der Waals dispersion force is proportional to the surface area).

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