Answer:
How do you arrange H20, H2S, Br2, and NaCI in increasing melting points?
Let’s review the basics: strong intermolecular (or inter-ion in the case of ionic solids) forces increase mp. Also, because it takes more energy to increase the kinetic energy of a molecule with increasing mass (KE = 1/2*m*v^2), increasing molecular weight generally increases MP within a common group (like alkanes).
So, strongest interactions are ionic. This makes NaCl the highest of the group (only ionic material). All others are molecules (non-ionic).
Let’s look at H2O and H2S. If you went by mass, H2O would have the lower MP. But molecules with O, N, and F are capable of strong intermolecular forces called hydrogen bonds. If you think “NO, I won’t Forget” you can remember that only N, O & F do this in combination with a hydrogen atom on the adjacent molecule. Water, due to hydrogen bonds has a much higher melting point than H2S.
This leaves Br2 and H2S. You may remember that Br2 is a liquid at room temperature. This suggests that it is next as H2S is a gas at room temperature. Br2 is very heavy and although it has no net dipole, the mass should make it worth consideration for the next spot.
