Answer to Question #61748 in Inorganic Chemistry for bharat

Question

Which noble
gas was discovered extra
-
terrest
rially before its discovery on
Earth?
What were the reasons fo
r late discovery of noble gases
?

Answer 1

Helium was first discovered not on Earth, but in the Sun. In 1868 French astronomer Pierre Janssen studied light from the Sun during a solar eclipse. He found proof that a new element existed in the Sun. He called the element helium.
For the next thirty years, chemists looked for helium on Earth. Then, in 1895, the English physicist Sir William Ramsay found helium in a mineral of the element uranium. Ramsay did not know why helium occurred in an ore of uranium. Some years later, the reason for that connection became obvious. Uranium is a radioactive element. A radioactive element is one that breaks apart spontaneously. It releases radiation and changes into a new element.
Two reasons for late discoveries of noble gases are:
1. They are present in extremely low concentrations in our environment.
2. The noble gasses are inert or unreactive. It is because they have fully filled electrons in their valence shell (the electronic configuration of noble gases is s2p6). Valence shell is responsible in defining reactivity as it took part at the time of bond formation.
Because most elements were discovered through their reactivity with other elements, typically with oxygen, it was difficult for scientists to work with a substance that seemed to have little or no chemical properties based upon the lack of reactivity.