Thursday, December 12, 2013

Argon Hydride in Space

Almost 1,000 years ago, the Chinese recorded a bright new object in the night sky. This is believed to be a star that exploded. The remnant of that exploded star is now called the Crab Nebula and it is about 6,500 light years from Earth.
Europe launched its Herschel Space Observatory in 2009, and in 2012 Astronomers used it to study the emission lines from Crab Nebula. What the scientists found were 2 bright emission lines from an area of shining dust. It was only by consulting databases of the known properties of different molecules that the scientists could finally identify these emission lines as coming from a very special molecule, argon hydride.
Argon hydride is special because it is the first time that molecules of a Noble Gas (Group 18) element have been found in space. On Earth, the naturally occurring Noble Gas (Group 18) elements are monatomic gases. Atoms of Noble Gas elements have a full valence shell of electrons so they tend not to react with other atoms.
Something really interesting must be happening in the Crab Nebula for argon hydride to be formed naturally. The researchers believe that the argon formed when the original star exploded. The intense energy of the explosion stripped electrons off the argon atoms, ionising them. Ionised argon atoms then reacted with hydrogen molecules to form argon hydride molecules.

M. J. Barlow, B. M. Swinyard, P. J. Owen, J. Cernicharo, H. L. Gomez, R. J. Ivison, O. Krause, T. L. Lim, M. Matsuura, S. Miller, G. Olofsson, E. T. Polehampton. Detection of a Noble Gas Molecular Ion, 36ArH , in the Crab Nebula. Science, 2013; 342 (6164): 1343 DOI: 10.1126/science.1243582

Further Reading

Suggested Study Questions:
  1. 1 light year is approximately 9.5 x 1015 metres. How far from Earth is the Crab Nebula in kilometres?
  2. 1 astronomic unit (1 AU) is approximately 1.5 x 1011 metres. What is the distance between Earth and the Crab Nebula in astronomic units?
  3. What sort of instrument can be used to observe the emission lines of hot gases?
  4. Explain how these emission lines are produced.
  5. Give the electron configuration of an atom of argon.
  6. With reference to the electron configuration of argon, explain why compounds of argon are not found naturally on Earth.
  7. Write an equation to show the loss of an electron from a gaseous argon atom.
  8. Explain how the hydride ion can be formed from a hydrogen atom.
  9. Give a likely molecular formula for a molecule of argon hydride.
  10. Is argon hydride most likely to an ionic compound or a covalent compound? Explain your answer.

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