Discovery of Noble Gases
In 1892 Lord Rayleigh found that oxygen was always 15.882 times more dense than hydrogen, no matter how it was prepared.
When he tried to extend this work to nitrogen, he found that nitrogen isolated from air was denser than nitrogen prepared from ammonia.
William Ramsey attacked this problem by purifying a sample of nitrogen gas to remove any moisture, carbon dioxide, and organic contaminants.
He then passed the purified gas over hot magnesium metal, which reacts with nitrogen to form the nitride.
3 Mg(s) | + | N2(s) |  | Mg3N2(s) |
When he was finished, Ramsey was left with a small residue of gas that occupied roughly 1/80th of the original volume.
He excited this gas in an electric discharge tube and found that the resulting emission spectrum contained lines that differed from those of all known gases.
After repeated discussions of the results of these experiments, Rayleigh and Ramsey jointly announced the discovery of a new element, which they named argon from the Greek word meaning the "lazy one" because this gas refused to react with any element or compound they tested.
Argon did not fit into any of the known families of elements in the periodic table, but its atomic weight suggested that it might belong to a new group that could be inserted between chlorine and potassium.
Shortly after reporting the discovery of argon in 1894, Ramsey found another unreactive gas when he heated a mineral of uranium.
The lines in the spectrum of this gas also occurred in the spectrum of the sun, which led Ramsey to name the element helium (from the Greek helios, "sun").
Experiments with liquid air led Ramsey to a third gas, which he named krypton ("the hidden one").
Experiments with liquid argon led him to a fourth gas, neon ("the new one"), and finally a fifth gas,xenon ("the stranger").
These elements were discovered between 1894 and 1898. Because Moissan had only recently isolated fluorine for the first time and fluorine was the most active of the known elements.
Ramsey sent a sample of argon to Moissan to see whether it would react with fluorine. It did not.
The failure of Moissan's attempts to react argon with fluorine, coupled with repeated failures by other chemists to get the more abundant of these gases to undergo chemical reaction, eventually led to their being labeled inert gases.
The development of the electronic theory of atoms did little to dispel this notion because it was obvious that these gases had very symmetrical electron configurations.
As a result, these elements were labeled "inert gases" in almost every text book and periodic table until about 30 years ago.
In 1962 Neil Bartlett found that PtF6 was a strong enough oxidizing agent to remove an electron from an O2 molecule.
PtF6(g) | + | O2(g) |  | [O2+][PtF6-](s) |
He therefore predicted that PtF6 might also react with Xe. When he ran the reaction, he isolated the first compound of a Group VIIIA element.
Xe(g) | + | PtF6(g) | [Xe+][PtF6-](s) | |
A few months later, workers at the Argonne National Laboratory near Chicago
Since that time, more than 200 compounds of Kr, Xe, and Rn have been isolated.
No compounds of the more abundant elements in this group (He, Ne, and Ar) have yet been isolated.
However, the fact that elements in this family can undergo chemical reactions has led to the use of the term rare gases rather than inert gases to describe these elements.
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