Order these molecules?

Question

order the following by cohesiveness:

ethanol

methanol

water

Answer 1

least to greatest = the way they are displayed

"Cohesiveness" probably means "Polarity" here. Polarity itself is an uneven charge distribution over the surface of a molecule. This makes the molecule act like a little magnet with positive and negative ends. The greater the separation of charge, the greater the polarity and also the higher the boiling point.

All three molecules have hydroxyl groups ("OH") which stick together because of weak Hydrogen bonds. The strength of the bonds depends on the polarity. Water is the most polar because the Oxygen atom is drawing charge away from the two Hydrogen atoms, making them relativly "positive". methanol is less polar because the carbon atom does not draw electrons away with the same strength that oxygen does. Ethanol has two carbon atoms, and as the chain of Carbon atoms gets longer, the carbon atoms have no effect on polarity at all. This is why oily substances with hudge carbon chains are completely non-polar.

Answer 2

water methanol ethanol