Argon is a noble gas with the symbol Ar and the atomic number 18. It forms no compounds accessible to the home chemist due to its inertness, which makes it suitable for inert atmospheres.
Argon is a colorless, odorless gas at standard conditions, with a boiling point of -185.848 °C and a melting point of −189.34 °C. It is heavier than air, with an density of 1.784 g/L. Unlike nitrogen, argon is 2.5 times more soluble in water, solubility similar to that of oxygen.
Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature. At 8 K, argon reacts with hydrogen fluoride, on a cesium iodide surface, resulting in argon fluorohydride, HArF, which is stable only under 17 K.
Argon is used as a shielding gas in welding, so many gas or welding supply stores will sell and rent out cylinders of pure argon or mixtures of argon and carbon dioxide (the more argon in the mixture, the more expensive it is).
A crude form of argon that is accessible to most people can be obtained from light bulbs, which may contain argon or a mixture of argon and nitrogen. This can be done by holding the bulb underwater, and slipping an open plastic bag around the bulb so that no air is in the bag. After sealing the bag, the light bulb can be broken, causing the inert gas inside to rise to the top while still trapped in the bag.
Argon can be separated from liquified air, although the process is very consuming and complicated due to argon's narrow liquid temperature range. It's best to buy argon cylinders.
As it takes no role in any chemistry, argon can be used as an inert atmosphere.
Creating an inert atmosphere in a home chemistry setting is difficult, and not often done. Nitrogen is usually used in the rare case it is attempted, and argon is called upon when nitrogen and carbon dioxide are unsuitable, as both carbon dioxide and nitrogen are cheaper gases than argon. For some processes that cannot be done in either of these atmospheres, the more expensive and difficult-to-find argon must be used. As argon is heavier than air, any container that is supposed to hold an argon atmosphere should have the opening above.
Argon is the choice in Schlenk lines and gloveboxes.
The most common use of argon is likely the preservation of samples or presentation in element collections.
Argon is inert and will not react with any compounds, making it safe to use. It may pose an asphyxiation hazard in closed rooms. Since it's heavier than air, it will accumulate on the lower part of a room.
Compressed argon should be stored away from heat.
Argon can be released in atmosphere, though best avoid closed spaces.