molecules) relative to its center of mass. Quantum mechanics predicts that, at room temperature and ordinary pressures, an isolated atom in a gas cannot store any significant amount of energy except in the form of kinetic energy. Therefore, when a certain number N of atoms of a monatomic gas receives an input ΔQ of heat energy, in a container of fixed volume, the kinetic energy of each atom will increase by ΔQ/N, independently of the atom's mass. This assumption is the foundation of the theory of ideal gases. In other words, that theory predicts that the molar heat capacity at constant volume cV,m of all monatomic gases will be the same; specifically, cV,m = R where R is the ideal gas constant, about 8.31446 J⋅K−1⋅mol−1 (which is the product of the Boltzmann constant kB and the Avogadro constant). And, indeed, the experimental values of cV,m for the noble gases helium, neon, argon, krypton, and xenon (at 1 atm and 25 °C) are all 12.5 J⋅K−1⋅mol−1, which is R; even though their atomic weights range from 4 to 131. The same theory predicts that the molar heat capacity of a monatomic gas at constant pressure will be cP,m = cV,m + R = R This prediction matches the experimental values, which, for helium through xenon, are 20.78, 20.79, 20.85, 20.95, and 21.01 J⋅K−1⋅mol−1, respectively; very close to the theoretical R = 20.78 J⋅K−1⋅mol−1. Therefore, the specific heat (per unit of mass, not per mole) of a monatomic gas will be inversely proportional to its (adimensional) relative atomic mass A. That is, approximately, cV = (12470 J⋅K−1⋅kg−1)/A cP = (20786 J⋅K−1⋅kg−1)/A Polyatomic gases Degrees of freedom A polyatomic molecule (consisting of two or more atoms bound together) can store heat energy in other forms besides its kinetic energy. These forms include rotation of the molecule, and vibration of the atoms relative to its center of mass. These extra degrees of freedom contribute to the molar heat capacity of the substance. Namely, when heat energy is injected into a gas with polyatomic molecules, only part of it will go into increasing their kinetic energy, and hence the temperature; the rest will go to into those other degrees of freedom. Thus, in order to achieve the same increase in temperature, more heat energy will have to be provided to a mol of that substance than to a mol of a monatomic gas. Substances with