atom - The smallest existing particle of a pure element that can exist and still maintain the properties (or chemical characteristics) of that element. It is made up of protons, neutrons, and electrons. Example: Nitrogen is an element. Nitrogen molecules (N2) are made up of two nitrogen atoms (N). Many elements exist in nature as molecules of one or more atom.
You have atoms and you have molecules. An atom is the basic building block of matter, the smallest piece of a chemical element.
A molecule will consist of two or more atoms joined together to become relatively stable. Atoms that form molecules undergo a chemical reaction, they react with other substances including atoms of the same matter.
True inert gases have atoms whose electrons are organized to be stable. The true inert gases consist of individual atoms. Examples are Helium (He), and Neon (Ne). Radon and Xenon are truly inert gases as well, I just cannot remember the exact chemical abbreviation tho I would guess Ra & Xe. Another name for a truly inert gas is a noble gas.
True inert gases do not react with anything, including themselves, they are a 'cloud' of single atoms.
N2 is an example of atoms of the same substance that react together forming molecules that share electrons to become a fairly stable 'cloud' of molecules.
The N2 molecule is stable until a lot of heat is added but N2 is not truly inert. You add enough heat at a high enough temperature, such as what occurs inside an internal combustion engine and that N2 will react and form the compounds in smog.
A lot of other substances create molecules with themselves, such as H2 and O2, but these gases are a lot less stable than N2. A little spark and they make water, compared to heating N2 up by a 1800 hundred plus degrees.
The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.