In the late 1800 s the British physicist Lord Rayleigh accurately determined the atomic masses of a number of elements, but he obtained a puzzling result with nitrogen. One of his methods of preparing nitrogen was by the thermal decomposition of ammonia: \( 2 \mathrm{NH}_{3}(g) \longrightarrow \mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \) Another method was to start with air and remove oxygen, carbon dioxide, and water vapor from it. Invariably, the nitrogen from air was a little denser (by about 0.5 percent) than the nitrogen from ammonia. Later the English chemist Sir William Ramsay carried out an experiment in which he passed nitrogen, which he had obtained from air by Raleigh's procedure, over red-hot magnesium to convert it to magnesium nitride: \(3 \mathrm{Mg}(s)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{Mg}_{3} \mathrm{~N}_{2}(s)= \)= After all of the nitrogen had reacted with magnesium, Ramsay was left with an unknown gas that would not combine with anything. The atomic mass of this gas was determined to be 39.95 amu. Ramsay called the gas argon, which means "the lazy one" in Greek. (a) Later Rayleigh and Ramsay, with the help of Sir William Crookes, the inventor of the discharge tube, showed that argon was a new element. Describe the type of experiment performed that led them to the conclusion. (b) Why did it take so long to discover argon? (c) Once argon had been discovered, why did it take relatively little time to discover the rest of the noble gases? (d) Why was helium the last noble gas to be discovered on Earth? (e) The only confirmed compound of radon is radon fluoride, \(\mathrm{RnF}\). Give two reasons why there are so few known radon compounds.

Step by step solution

01

Answer for sub-question (a)

The experiment that led them to the conclusion that Argon was a new element consisted of getting a sample of nitrogen from air, removing impurities and then heating it with red-hot magnesium. This process formed magnesium nitride, leaving behind a gas that wouldn't combine with any other element. This gas was Argon. Analyzing its atomic mass and properties, they were able to conclude that it was indeed a new element.

02

Answer for sub-question (b)

The discovery of Argon took a long time mainly due to its reactivity. Being a noble gas, Argon is inert and does not readily participate in chemical reactions. This property makes it hard to detect and isolate. Moreover, it also required the technology and scientific understanding to be at a level where such a sophisticated procedure could be carried out.

03

Answer for sub-question (c)

Once Argon was discovered, it provided a framework and understanding of the properties and behaviour of noble gases. Scientists were then able to use this knowledge, along with improvements in technology and experimental procedures, to discover the rest of the noble gases in relatively less time.

04

Answer for sub-question (d)

Helium was the last noble gas to be discovered on Earth because it is lighter than air and tends to escape upwards in the atmosphere. It's also very unreactive, due to which it does not readily form compounds, making it hard to detect.

05

Answer for sub-question (e)

There are very few known Radon compounds due to two reasons. First, Radon is a noble gas, which makes it very unreactive and less likely to form compounds. Second, Radon is radioactive and has a very short half-life. This makes studying and handling it for experimental purposes quite difficult and dangerous.

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