Boiling point

Moderators: Chem_Mod, Chem_Admin

Madeline Lequang 1G
Posts: 30
Joined: Fri Sep 28, 2018 12:27 am

Boiling point

Postby Madeline Lequang 1G » Fri Nov 09, 2018 10:13 am

What did he mean in lecture today by a rod shaped boiling point and a spherical boiling point in his example today?

Stephen Sirmay 1I
Posts: 30
Joined: Fri Sep 28, 2018 12:21 am
Been upvoted: 1 time

Re: Boiling point

Postby Stephen Sirmay 1I » Fri Nov 09, 2018 11:02 am

I have in my notes that Instantaneous dipoles in two nearby rod shaped molecules are closer and therefore stronger than those in two nearby spherical shapes . Hope this helps!

Jovian Cheung 1K
Posts: 48
Joined: Fri Sep 28, 2018 12:16 am

Re: Boiling point

Postby Jovian Cheung 1K » Fri Nov 09, 2018 12:55 pm

Rod-shaped and spherical-shaped are used to describe the shape of the molecule.

Since rod-shaped/longer molecules have more contact surface area when packed together --> more surface for intermolecular forces and attractions, they tend to have a higher boiling point.

Spherical-shaped molecules don't have this 'advantage', and thus have a lower boiling point.

Hannah Yates 1K
Posts: 59
Joined: Fri Sep 28, 2018 12:27 am

Re: Boiling point

Postby Hannah Yates 1K » Fri Nov 09, 2018 3:43 pm

Rod and spherical shaped were just an example of two possible shapes. He then used pentane and 2,2-dimethylpropane as two examples of those shapes. Pentane is rod shaped and 2,2-dimethylpropane is spherical. Pentane has a higher boiling point because the intermolecular forces are stronger because the shape allows the molecules to get closer.

Mona Lee 4L
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

Re: Boiling point

Postby Mona Lee 4L » Fri Nov 09, 2018 4:24 pm

You can think of "rod" vs. "sphere" as straight-chain vs. branched molecules. Essentially, straight chain molecules are going to have fewer atoms "sticking out." so they can pack closer together, increasing the LDF.

Vana Mirzakhani 3I
Posts: 62
Joined: Fri Sep 28, 2018 12:24 am

Re: Boiling point

Postby Vana Mirzakhani 3I » Fri Nov 09, 2018 5:05 pm

To add on, spherical shaped molecules have lower boiling points, usually 10°C, and rod shaped molecules have higher boiling points, usually 36°C.

Hilda Sauceda 3C
Posts: 76
Joined: Fri Sep 28, 2018 12:24 am

Re: Boiling point

Postby Hilda Sauceda 3C » Sun Nov 11, 2018 11:52 am

The rod and spherical shaped molecules have different boiling points which is why they have different shapes. With spherical shaped molecules having a lower boiling point.

Jaedyn_Birchmier3F
Posts: 30
Joined: Fri Sep 28, 2018 12:26 am

Re: Boiling point

Postby Jaedyn_Birchmier3F » Sun Nov 11, 2018 5:35 pm

A rod shape has a higher boiling point than a spherical shape because the shape has an effect on how much attraction an atom feels to another atom. Rod shape would have a higher boiling point because the attractive forces are closer, therefore the bond is stronger and needs more heat to break.

Margaret Akey
Posts: 80
Joined: Fri Sep 28, 2018 12:18 am

Re: Boiling point

Postby Margaret Akey » Sun Nov 11, 2018 5:36 pm

how do you know whether it has a rod or spherical shape?

Shivangi_2J
Posts: 65
Joined: Fri Sep 28, 2018 12:15 am

Re: Boiling point

Postby Shivangi_2J » Sun Nov 11, 2018 6:08 pm

I think organic compounds are generally rod-shaped. Also, the way the formula is written generally gives you an idea of whether it is rod/sphere shaped. For example, in Lavelle's lecture, he mentioned the examples C4H10 and CH3CH2CH2CH3. These both have the same number of each atom but the latter is written as a chain and is rod-shaped

MaggieMatern_Dis1H
Posts: 30
Joined: Fri Sep 28, 2018 12:19 am

Re: Boiling point

Postby MaggieMatern_Dis1H » Tue Nov 13, 2018 1:16 pm

A rod or oval shaped molecule has more surface area with which it can interact with another oval molecule, increasing the VDW interactions between the two, making the bond stronger, harder to break, and resulting in a higher melting point.

A circular molecule has less surface area with which it can interact with other molecules, and so by the same logic, it has a lower melting point.

You can look at the molecular shape and structure to determine whether a molecule will have more or less surface area.

Madelyn Romberg 3L
Posts: 29
Joined: Tue Oct 02, 2018 12:16 am

Re: Boiling point

Postby Madelyn Romberg 3L » Thu Nov 15, 2018 12:00 pm

A rod shaped molecule has stronger intermolecular forces, meaning they have a stronger attraction to each other. To break this stronger connection requires more energy, resulting in a higher boiling point. The opposite is true for the spherical shape.

pamcoronel1H
Posts: 45
Joined: Fri Sep 28, 2018 12:25 am

Re: Boiling point

Postby pamcoronel1H » Thu Nov 15, 2018 5:45 pm

If a nonpolar rod-shaped molecule is interacting with another nonpolar rod-shaped molecule, they are more likely to find areas of attraction by London forces because their shape allows them to have multiple points of contact.

A spherical molecule on the other hand, has less points of contact with another spherical molecule because only one side of each is able to interact with the other through London forces.

Because rod-shaped molecules are more strongly attracted to each other, they are more tightly packed together and so a higher boiling point is needed to break those bonds apart.

Image


Return to “Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)”

Who is online

Users browsing this forum: No registered users and 1 guest