Chobhi's Blog

I remember when I was young, I liked stretching on a black sofa almost upside-down and reading a book. My mother would come and implore me to go out and I would be oblivious to her presence. “Why aren’t you reacting? It is as if you are in another world!”, she would remark in dismay.
Sometimes, when I look at the last group in the Periodic Table, the Noble Gases, I wonder if they too belong in another world. Helium,He, neon, Ne, argon, Ar, krypton,Kr, xenon, Xe and radon, Rn are the six common noble gases. All these are obviously gases and the outer electronic structure is a stable octet, which is really a ns2 np6 configuration, where n=2 through 6. The exception is helium, which has a stable duplet or 1s2 structure.
One has already seen that the alkali and alkaline- earth elements try to lose one or two electrons to achieve the stable noble gas structure. In addition we have seen that the halogens gain an electron to have the outer stable electronic structure of noble gases. In fact, almost all elements in the periodic table gain or lose electrons during a chemical reaction to get to the stable electronic structure of these noble or inert gases. This also implies that the last group elements are not reactive. Now is that really a fact?
Till the early 60’s, scientists were talking about the stable octet/duplet rule to justify the non-reactive nature of these gases. Initially it was called Group 0 for this reason. In 1962 and 1963,scientists observed that some of the noble gases,like radon, krypton and xenon form different flourides. In addition, in 2006, scientists in Dubna, Russia, announced that the element 118, the next noble gas, was synthesized in 2002 and 2005 in a cyclotron.(Ref.1) A cyclotron is a high particle accelerator where subatomic particles like protons and electrons are in a magnetic and electrical field and can collide at high speeds with each other.(Ref.2)
Hence there are really 7 noble gases present and since some of them are not completely non-reactive, the noble gases group is now called Group 18 and not Group 0.(Ref.1)
The noble gases are all colorless, odorless, tasteless, non-flammable gases. They also happen to be mono-atomic gases, ie, they exist as individual atoms rather than di- or poly- atomic molecules.(Ref.3) They were originally called inert or rare gases. They are neither inert(since we know some of them react with flourine to form compounds) nor rare, because several of them are found in abundance on earth.(Ref.1) Yet the word’noble’ is appropriate, since certain elements like gold or platinum are also considered ‘noble metals’ because of their reluctance to undergo chemical reactions easily.(Ref.1)
How abundant are these noble gases? It is noted that their abundance decreases with increase in atomic weight, with He being the most abundant while there are only three molecules of element 118! Most of the noble gases are present in the earth’s atmosphere, except for helium, radon and are recovered from the air by obtaining them as liquids and conducting fractional distillation to separate them.(Ref.1) (Fractional distillation is a technique whereby different liquids can be distilled/condensed using differences in their boiling points, to collect each substance separately.)
Actually both radon and even helium are by-products of radioactive decay. After the discovery of radium by the Curies, German physicist became fascinated with radium and discovered a gas that it emitted and he called it ‘radium emitting; he discovered the new element, radon. The breakdown of radium as well as uranium can lead to the production of helium ions as well.(Ref.3)
The noble gases are used in many daily and specialized applications. Helium as we already know has been used in the filling of balloons, for large airships and for children. Helium is also used by divers not for buoyancy but to prevent “the bends” a condition when nitrogen bubbles in the blood as a diver comes up to the surface. Helium is extensively used in the field of cryogenics which is low-temperature science. Neon is best known for its use in neon signs, neon glow lamps are used to indicate on/off signs in electronic instrument panels and in early televisions. Even though radon is considered a hazard it has its uses in earthquake detection, leaks, measuring flow rates. Paleontologists, who study the distant past as well as geologists use argon dating to study volcanic layers, fossils etc. Krypton is mixed with argon in the manufacture of windows with high thermal efficiency, used in lasers as well as halogen headlights. Along with xenon, especially because of its lower cost, krypton has been used as a fuel in space.
(Ref.3)
As one can see, these noble gases are not so quiet and inert as they seem.
Activities for Middle School Teachers:
Have a discussion with students about how certain words like ‘inert’, ‘rare’ to describe the Group 18 gases is really not accurate. Look at the history of the ‘phlogiston’ theory and how the burning/oxidation theory was modified with further experiments in science. Look at the history of the atomic models and see how those models evolved with time and more knowledge. How did the invention of new instruments in the laboratory aid these developments? Compare the evolution of ideas in chemistry, physics with say, social sciences and psychology.
Nuggets of Information:
In 1868, a French astronomer named Pierre Janssen (1824-1907)came to India to observe a total solar eclipse. Using a spectroscope, an instrument for analyzing the spectrum of light emitted by an object, Janssen was able to show a yellow line in the spectrum, never seen before, which seemed to indicate the presence of a previously undiscovered element. He called it “helium” after the Greek god Helios, or Apollo, whom the ancients associated with the Sun.(Ref.3)
Helium is remarkable since it only liquefies close to absolute zero(-272 degrees celcius); that makes it very difficult to liquefy from air.(Ref.3)
Almost all the noble gases have derived their names from the Greek language. Neon comes from the word ‘neos’ which means new,argon from ‘argos'(inactive), krypton from kryptos,(hidden) and xenon from the word ‘stranger’.(Ref.3)
Superman’s kryptonite is an imaginary substance and has no relationship with the noble gas krypton.(Ref.3)
The discovery of radon starting with the element radium was the first clear proof of one element being transformed to another element through radioactive decay. (Ref.3)
Within the atmosphere,, argon is considered the most ‘abundant’ of these gases, about 0.93%.(Ref.3)
Until 1988, most Americans had no knowledge of the existence of radon, when the EPA(Environmental Protection Agency) released a report indicating the harmful effects of radon in homes. From the 80s through the 90s radon detector sales boomed; even today when a house is sold, radon levels need to be checked. This is especially needed if a house has been weather-sealed to improve heating and cooling.(Ref.3)
Chinese scientists made an interesting discovery in the 1960s. Radon levels in groundwater increased significantly before an earthquake. These scientists monitor radon levels to predict earthquakes.(Ref.3)
References:
1.http://www.britannica.com
2.http://www.thefreedictionary.com/cyclotron
3.encyclopedia.com/topic/Noble_gases.aspx

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