# Why do some gases have fewer degrees of freedom at same temperature?

I am trying to understand the degres of freedom for gases. Air has 5 degrees of freedom at room temperature but why does Argon, $$Ar$$ have 3 degrees of freedom while $$O_2$$ has 5 at the same temperature (at 1 atm) and 3 at 100K?

I looked up the boiling temperature for oxygen and it is $$-183^oC=90K$$ and it is well below room temperature for both. If the boiling point is well below the room temperature for both $$Ar$$ and $$O_2$$, I thought that all atoms now have so much energy that they move (3 degrees), rotate (2 degrees) and vibrate (2 degrees) = 7.

• @Clone You could look at a plot of the specific heat (at constant volume) as a function of temperature, since $c_v = Nk/2$, where $N$ is the number of degrees of freedom. But I don't know of any definitive reference. Oct 26, 2020 at 2:13