It's a question on my quiz which I guessed right and couldn't do the reasoning:
Based on the intermolecular forces, predict the boiling points of the following substances and list them in the order of increasing boiling point. State your reasons accordingly.
- Dimethyl ether $(\ce{CH3OCH3})$
- Ethanol $(\ce{CH3CH2OH})$
- Propane $(\ce{CH3CH2CH3})$
Right away, I see the hydrogen bond in ethanol, so it must have the highest boiling point.
I couldn't decide on the other two, so I drew lewis structures (kind of) for both
I ignored the hydrogens because they don't affect the polarity (correct me if my lewis strctures are wrong).
This is what I guessed, and I was right. When my teacher takes this question up, he said that propane is non polar, which means it only interacts via london forces, which means it has the lowest boiling points out of these three.
But how is propane non polar though, when I asked, he said "I don't have an answer for this, life is hard."
I mean, if I draw the structure in the bad way, it does look symmetrical and balanced out:
But if I draw it in this way, it doesn't help me when I'm trying to figure out the polarity, because everything will look non polar. I can even say water is in a linear shape because the H's and the O line up perfectly in a line, which is not the correct picture of reality.
My biggest question is, how do I figure out if something is polar or not.