2013 midterm Q5 [ENDORSED]

[Jineava_To_3N]

Arrange the following in order of increasing standard molar entropy: CHF3(g), CF4(g), CH3F(g), CH2F2(g)
The answer says it is CH3F<CH2F2<CHF3<CF4

But why does CF4 have the largest molar entropy when its carbon atom is surrounded by 4 fluorine atoms? Shouldn't that indicate its number of possible positions is less than the other molecules?

[Chem_Mod]

Molar entropy increases as follows: solid < liquid < gas. Since these are all gasses, we must look at what each gas is made of. Each gas molecule is made up of 5 different atoms. However, each Hydrogen atom is made up of 1 proton and 1 electron. A Fluorine atom has 9 protons and 9 electrons. Not only is Fluorine larger than Hydrogen, but having more protons/electrons, there are more "options" for the position of each electron. Think of it as each electron in Fluorine has 9 different positions it can be in, while the sole electron in Hydrogen only has 1 position it can be in. The more possible positions, the higher the entropy. Thus CH₃F has the lowest entropy while CF₄ has the highest entropy.