Are there electron or proton receptors in our nose?
Chloride (Cl2) carries 34 protons and electrons. 

A common example of a relatively heavy odorless gas is CO2, carrying 22 protons and electrons. 

All noble gases are odorless. The heaviest, naturally occurring noble gas is Radon, which has a proton count of 86. Ununoctium, an exotic artificial element with atomic number 118, is a noble gas too. However, with a half life of approximately 0.9 ms it's difficult to sniff out whether it's really oderless. 

Sulfur hexafluoride is odorless too, with a proton count of 72.  

Hence, the atomic number per se is not the determining factor reason for generating the sensation of odor. 

What determines whether a compound generates the sensation of odor I am unsure of, but the above compounds mentioned are all chemically inert. Note that Ununoctium decays rapidly, it doesn't react with anything. I have not been able to verify whether inertness always means odorless, but with the above examples I am inclined to believe it holds true. However, the reverse is definitely not true, as carbon monoxide is odorless, but reactive.