Argon is an inert gas in group VIII A of the periodic table with atomic number 18, an atomic weight of 39.948, and a density of 1.40 Mg/m 3. In the solid state it forms an fcc crystal with a melting ...

Like all noble gases ... Mendeleev's first periodic table did not include them, as closed-shell elements remained undiscovered until Lord Rayleigh and William Ramsey isolated argon in 1894.

They named this gas argon from the Greek for lazy or inactive to reflect its extreme inertness. The problem was, where did this new element fit into Mendeleev's periodic table of the elements? There ...