# How to estimate the physical size of a molecule?

I'm reading some chemistry-related papers that employ concepts of droplet evaporation. Since I am no chemist, I am wondering:

How can I estimate the actual size of a molecule, say succinic acid?

An order of magnitude would suffice. I'm aware of the fact that most molecules can not be approximated by simple assuming that they are spherical.

Evidently, I don't want to do this bottom-up from quantum mechanics. A broad explanation or just a reference would suffice.

-
I'm going to have a wild guess, $1.26\cdot10^{-22}\,\mathrm{cm}^3$, and wait for an actual answer... :) –  Glen The Udderboat Jun 11 '13 at 13:27
Perhaps (I'm a total nitwit), you may also have a look at structure of the molecule, plug in a few bond lengths, some angles and some room for electrons, and... perhaps get something similar. –  Glen The Udderboat Jun 11 '13 at 14:34
@Gugg thanks, this is a classic example of turning a simple problem into smth overly complicated. :-) –  lomppi Jun 11 '13 at 14:38
Shouldn't this go to ChemestrySE? –  jinawee Jun 11 '13 at 15:54
@jinawee It would have been on-topic there too, but the physical scale of molecules comes up in a lot of physics contexts (crystalography, various questions of quantum limits in semiconductor design and other condensed matter topics, attosecond physics, and so on). –  dmckee Jun 11 '13 at 16:59

The order of magnitude given by Gugg is correct. The molar volume for the succinic acid is

$V_m=\frac{M}{\rho}=\frac{118.09}{1.59}\frac{cm^3}{mol}=74.27cm^{3}/mol$

where $M$ is the molar mass and $\rho$ the density. From this, you find the volume of the molecule to be

$V_{molec}=\frac{V_m}{N_A}=1.23\cdot10^{-22}cm^3$

-
thanks. this is why I love this site! :-) –  lomppi Jun 11 '13 at 14:39