[UOIT]

Why does CH2Cl2 solvent (lower layer) have higher density than water while non-chlorinated solvents like hexanes and ether (top layer) have lower density than water, i.e. what exactly is it about Cl that causes this difference?

[Yarr]

The precise cause is the fact that chlorine is heavier than oxygen, while carbon is lighter.

[UOIT]

Thank you!!

[sjb]

The precise cause is the fact that chlorine is heavier than oxygen, while carbon is lighter.

Well, I wouldn't quite go that far, otherwise you run into difficulties explaining why H₂S is less dense than H₂O (at rtp), even though sulfur is heavier than oxygen...

S

[UrbanBlues]

Well, Sulfur is less electronegative (2.4) than Oxygen (3.5). Hydrogen-Sulfur bonds are less polar, hence molecules are less attracted by the other molecules. So, as the 'packing' is reduced, the density is a little bit lower ... Hydrogen bonds have a tremendous impact on property, as the boiling point of H20 (100 °C) compared to the point of H2S (-60 °C)

[Yarr]

otherwise you run into difficulties explaining why H2S is less dense than H2O

Well that's simple: hydrogen sulphide is a gas, while water is a liquid.