Argon is one of the inert gases. Once they were called “noble” gases because they apparently didn’t mix with the more “common” elements! It actually is possible to create compounds with argon but it’s not something of much interest. Argon gas makes up about one percent of our atmosphere. One percent may not sound like much but the earth is big and it is surrounded by a big ring of gases so there is a lot of argon in our world.
Most people know about argon because of welding. Inert gases are used to bathe or blanket welding electrodes and the welds they produce to prevent oxidation. Our atmosphere is about 20% oxygen which is why we can live in it. But oxygen is potent stuff. It reacts readily with many things, especially metals. Welds are used to join metals and involve melting and fusing. Welds come out better when they are free of contaminants. One of the chief contaminants is air with all its attendant particles, and the other big contaminant is oxygen. Argon and other inert gases like xenon are used in many manufacturing processes where something has to be protected from air (and thus oxygen).
Double-pane windows often have argon gas in the gap rather than air. Argon is denser than air and thus a better insulator. Air is about 80% diatomic nitrogen (N2) and about 20% diatomic oxygen (O2). Nitrogen has an atomic mass of 14 and oxygen 16. Thus the mass of a mole of air is [0.8*(14*2)] + [0.2*(16*2)] which is 22.4 + 6.4 or 28.8 mass units. Argon has an atomic mass of 39.9 so a mole of of it is nearly 40% heavier. (Actually as I mentioned earlier air is about 1% argon so I’d have to adjust my nitrogen number to 79% but the difference is small.)
Other inert (noble) gases are helium, neon, krypton, xenon, and radon. They make up the right-most column or group number 18 of the periodic table. All have filled electron shells and that is the main determinant of their chemical behavior. Argon is obtained by the fractional distillation of liquefied air.