Intermolecular Bonding of CH4: Van der Waals

[brake4country]

Homework Statement

What type of intermolecular bonding occurs in gaseous CH₄?
(A) covalent
(B) ionic
(C) hydrogen
(D) van der Waals

Homework Equations

The Attempt at a Solution

Here is what I did: ruled out B (not ionic) and chose A. The correct answer is D. Is C wrong because hydrogen bonding only happens between polar molecules? Why is D correct over A? Is it because covalent = intramolecular, not intermolecular? Thanks in advance.

 

[Simon Bridge]

Physically a covalent bond involves sharing electrons.
The image is that electron orbit both whatsits concerned.
This requires the whatsits to get very close to each other: the range is of order of an Angstrom.

Do individual CH4 molecule share electrons with each other?

 

[brake4country]

The C shares electrons with the hydrogens to complete their shells. This answer should be covalent.

 

[Simon Bridge]

Does the C share it's electrons with H atoms in other molecules?

 

[brake4country]

No it doesn't. It's a non-polar molecule. In researching, I learned that hydrogen bonding is not applicable here because CH4 is not polar. Therefore, the "intramolecular" forces are covalent, but that's not what the question is asking. The question asks "intermolecular" forces which exist between atoms. Ionic, covalent, and hydrogen bonding our out; leaving van der waals forces.

I think I get it now. If I am missing something, please share! Thanks!

 

[Simon Bridge]

That's right - the question was basically about whether you understood the difference between inter and intra molecular forces. Covalent and Ionic bonds are intra-molecular: they are what holds molecules together.

There is a good summary:
http://www.chem.ufl.edu/~itl/4411/lectures/lec_g.html
... Van-der Waals forces are the sum of Keyson, Debye, and London forces.