intermolecular forces

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halle young 4A
Posts: 68
Joined: Thu Jul 11, 2019 12:16 am

intermolecular forces

Postby halle young 4A » Wed Nov 13, 2019 11:17 am

homework problem 3F.1
Identify the types of attractive intermolecular interactions that might arise between molecules of each of the following substances:
(a) NH2OH (b) CBr4 (c) H2SeO4 (d) SO2

i understand that London interactions happen for all molecules and i understand when there is a hydrogen bond, but how do you know when a molecule has a dipole-dipole interaction and why does a and c have that and not d?

Brian Tangsombatvisit 1C
Posts: 119
Joined: Sat Aug 17, 2019 12:15 am

Re: intermolecular forces

Postby Brian Tangsombatvisit 1C » Wed Nov 13, 2019 11:22 am

There are only dipole - dipole interactions when the overall molecule has a dipole. This is the case for a) and c) since the dipoles within the molecule do not cancel each other out and result in an overall dipole moment for the entire molecule. However, for d), even though the s-o bond is polar, the dipole moments cancel each other out since the molecule is linear and symmetrical. Therefore, the overall molecule would not have a dipole moment and there would be no dipole - dipole interactions since the molecule is actually nonpolar.

halle young 4A
Posts: 68
Joined: Thu Jul 11, 2019 12:16 am

Re: intermolecular forces

Postby halle young 4A » Wed Nov 13, 2019 11:28 am

How do you know when the overall molecule has a dipole?

Cynthia Gong 1L
Posts: 51
Joined: Fri Aug 09, 2019 12:15 am

Re: intermolecular forces

Postby Cynthia Gong 1L » Wed Nov 13, 2019 11:32 am

An overall molecule has a dipole if there is a great difference in electronegativity between the individual atoms that compose that molecule.

anjali41
Posts: 109
Joined: Fri Aug 09, 2019 12:15 am

Re: intermolecular forces

Postby anjali41 » Wed Nov 13, 2019 11:36 am

A good example to think of is a water molecule. There is a great difference in electronegativity between the Oxygen and Hydrogen, so the molecule is not balanced in a way. So you know the water molecule is a dipole.

ALegala_2I
Posts: 102
Joined: Thu Jul 11, 2019 12:17 am

Re: intermolecular forces

Postby ALegala_2I » Wed Nov 13, 2019 11:39 am

Dipoles occur when there is an unequal sharing of electrons. Each atom in a molecule has a partial charge which is either negative or positive. When one charge is significantly larger than another, or the electronegativity difference is great, a dipole is produced. Lone pairs on the central atom also create a dipole, making the molecule polar. When dipoles cancel out and opposite charges are similar, the molecule is considered nonpolar.

Angela Patel 2J
Posts: 110
Joined: Sat Aug 24, 2019 12:17 am

Re: intermolecular forces

Postby Angela Patel 2J » Wed Nov 13, 2019 12:13 pm

Are we expected to memorize electronegativities in order to tell whether a molecule has a dipole? And what is the difference between dipole and london forces?

Dakota Walker 1L
Posts: 58
Joined: Wed Sep 18, 2019 12:17 am

Re: intermolecular forces

Postby Dakota Walker 1L » Wed Nov 13, 2019 6:38 pm

When googling information about SO2 I found that it was bent, polar and has dipole-dipole interactions. Does anyone know if this is true? And if it is, why is the molecule bent?

derinceltik1K
Posts: 51
Joined: Sat Aug 17, 2019 12:15 am

Re: intermolecular forces

Postby derinceltik1K » Wed Nov 13, 2019 10:01 pm

No we are not expected to know the electronegativities. If we need to use them in a question they would include them in the question as a footnote.


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