Intermolecular forces HELP ASAP PLS (1 Viewer)

[Bob99]

Hi I am still confused about the various intermolecular forces such as disperion, dipole dipole, hydrogen bonding, POLARITY and what not. Can someone pls give a generalised explanation about when these forces occur with reference to organic chem? Any help is appreciated thanks.

 

[someth1ng]

Generally, it all comes down to positive and negative charges being attracted.

Dispersion forces: electron distribution fluctuates over time, so even "non-polar" compounds will have an uneven distribution of charge (but are only instantaneous).
Dipole-dipole: polar compounds will have an overall biased distribution of electron density (i.e. some parts are partially charged), which can be used to attract other molecules.
Hydrogen bond: a special type of dipole-dipole bonding, which usually arises between a N, O, or F and a hydrogen atom bonded to another N, O, or F. It's a bit stronger because there's more charge separation (and better matched orbital sizes, but that's another story).

 

[Bob99]

thank you for that information. Also, when given a structural diagram of an organic compound, how do we verify that it is polar/non-polar? Is there something we have to look for?

Generally, it all comes down to positive and negative charges being attracted.

Dispersion forces: electron distribution fluctuates over time, so even "non-polar" compounds will have an uneven distribution of charge (but are only instantaneous).
Dipole-dipole: polar compounds will have an overall biased distribution of electron density (i.e. some parts are partially charged), which can be used to attract other molecules.
Hydrogen bond: a special type of dipole-dipole bonding, which usually arises between a N, O, or F and a hydrogen atom bonded to another N, O, or F. It's a bit stronger because there's more charge separation (and better matched orbital sizes, but that's another story).

 

[jekyll]

Also, when given a structural diagram of an organic compound, how do we verify that it is polar/non-polar? Is there something we have to look for?

probably not the best way but basically:

polar:
- h2 bonding (H-O, F, N)
- unsymmetrical

non-polar
- diatomic molecules
- nobel gases
- C-H bonding
- symmetrical

if i got this wrong someone please correct me

 

[someth1ng]

probably not the best way but basically:

polar:
- h2 bonding (H-O, F, N)
- unsymmetrical

non-polar
- diatomic molecules
- nobel gases
- C-H bonding
- symmetrical

if i got this wrong someone please correct me

• In reality, polarity is a spectrum, not a binary property.
• It's best to consider the vectors (i.e. arrows denoting positive to negative) for each bond and consider their electronegativities.
• Symmetry works around a single atom but it's not good when considering a larger molecule. For example, ethylene glycol is a polar compound that has an axis of symmetry. However, the polarity of the hydroxyl groups outweighs the symmetry.
• Diatomic molecules can be polar (e.g. HF, HCl). Only elemental diatomic molecules (e.g. N2, O2, Cl2, F2) are non-polar.

 

[Bob99]

• In reality, polarity is a spectrum, not a binary property.
• It's best to consider the vectors (i.e. arrows denoting positive to negative) for each bond and consider their electronegativities.
• Symmetry works around a single atom but it's not good when considering a larger molecule. For example, ethylene glycol is a polar compound that has an axis of symmetry. However, the polarity of the hydroxyl groups outweighs the symmetry.
• Diatomic molecules can be polar (e.g. HF, HCl). Only elemental diatomic molecules (e.g. N2, O2, Cl2, F2) are non-polar.

Thank you so much for your help @someth1ng and @jekyll I really appreciate it