Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Heaviest Gas
Name: Bhola
Status: N/A
Grade: 9-12
Location: N/A
Country: N/A
Date: 9/25/2005

While I was learning about carbon dioxide, it was written in my book that it is the heaviest gas. What is the reason behind being heavy? Does heaviness have some relation with molecular weight?

Whether a substance is a gas, liquid, or solid depends on the temperature as well as the molecular weight so which gas is "heaviest" depends upon the temperature, pressure and what composition restrictions you want to place on the class of substances. The molar density of a gas is given fairly accurately by the ideal gas law: PV=m/MRT, where R=0.082 liter-atm/mol kelvin, m = the mass, M = molecular weight, and T is in kelvins, with P in atmospheres and V in liters. Of the permanent stable ELEMENTS at room temperature xenon, Xe, is the most dense with a molecular weight of 131.293. Radon, Rn is more dense with an approximate molecular weight of 222 but it is radioactive. So it is a little misleading to even ask the question which gas is "heaviest" without specifying what I discussed above.

Vince Calder

Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory