Elements

Noble Gases – Periodic Table

What are the Noble Gases

The noble gases are a group of six unreactive, inert gases on the far right side of the periodic table. They are members of group 18, the last group on the periodic table.

All of the noble gases occur in the atmosphere. In fact, air is 0.934% argon – the other elements are present in much smaller quantities. Most of the argon in the air was produced by the decay of radioactive potassium-40. Neon makes up .0018% of air, helium .00052%, krypton .00011%, and xenon .000009%.

Properties & Uses of the Noble Gases

The noble gases are tasteless, odorless, colorless, nonflammable, and mostly nonreactive. These monatomic elements also conduct electricity and can fluoresce. Because of their nonreactivity, one organic chemist even referred to them as the “lazy elements’. But Neil Bartlett showed us another side to these elements in 1962.

The noble gases all have very low melting and boiling points, due to their weak intermolecular forces. They are all very close to being ideal gases. Noble gases are monoatomic, unlike the halogens. Helium is the only element that cannot be frozen at room temperature.

Helium is used in blimps and balloons, and in deep-sea diving, aka technical diving – mixed with oxygen. Most helium comes from natural gas, and some people worry that we may run out of helium one day. Argon is used in incandescent lamps, and neon is used in signs. Both helium and neon are used as cryogenic refrigerants.

Xenon has been used as an anesthetic, albeit a costly one. Radon is a product of the radioactive decomposition of radium compounds.

Noble gases are often used in fluorescent lighting and discharge lamps. This is because they easily emit electromagnetic radiation. When an electrical discharge is passed through a noble gas at low pressure, the gas will glow. Each noble gas glows a different color, e.g. neon is red-orange, like in neon signs. Xenon glows blue, and krypton glows a whiteish purple.

List of all Noble Gases

The list of all noble gases includes helium, neon, argon, krypton, xenon, and radon. Oganesson, atomic number 118, was formed in 2006. It may also be a noble gas, but very little is known about it.

History of the Noble Gases

When Lord Rayleigh and William Ramsay discovered argon in 1895, the scientific world was surprised. They had not predicted any elements could lie between the halogens and the alkali metals. In the following three years, Ramsay would go on to discover helium, neon, krypton, and xenon.

Originally these elements were called inert gases, or rare gases. The phrase noble gas comes from the German world Edelgas, used first in 1898 by Hugo Erdmann, the same year radon was first identified. It is now known, that several of these elements are quite abundant on earth. Helium is the second most abundant element in the universe, after hydrogen. It is also now known, that many of the gases are not completely inert.

Noble gas inside a buckminsterfullerene molecule,
Noble gas atom held within a buckminsterfullerene molecule, which is 60 carbon atoms. Rendition by Hugo Alejandro Jimenez Vazquez

Noble Gas Chemistry

For a long time, it was thought that these gases could not bond with other elements. We now know that is incorrect, in fact, the further down the group you go, the more reactive the noble gases get. Xenon can form several compounds with fluorine. However, it is quite difficult to get xenon and krypton to form compounds.

Linus Pauling predicted in 1933 that xenon and krypton could form compounds, and he was correct. In 1962, Neil Bartlett used platinum hexafluoride to form a compound between xenon, platinum, and fluorine – xenon hexafluoroplatinate, Xe[PtF6]. Interestingly, it was a mustard yellow solid compound. Since then, many compounds of xenon have been formed, along with some compounds of krypton, and with much difficulty, argon fluorohydride – HArF. XeF2, XeF4, and XeF6 were all produced shortly after the first xenon compound was announced.

Trapped in a Fullerene

It was found that noble gas atoms can be “caged” inside a buckminsterfullerene molecule. A fullerene molecule, depicted in the image above, consists of a large number of carbon atoms in a polyhedral shape – with a 60 carbon structure being particularly stable. The noble gas is pushed inside the molecule when heated to 6500 Celsius under 3000 atmospheres pressure of one of the gases. When an atom is trapped in the center, it is called an endohedral fullerene.

Why are the Noble Gases Unreactive?

All of the noble gases have a full outer shell, with the maximum number of valence electrons. This electron configuration is extremely stable, and it takes a large amount of energy to remove an electron from this stable configuration.

Fun fact about the Noble Gases

  1. In Antarctica, it gets so cold that radon could be a liquid there.
  2. All of the noble gases are soluble in water, and radon is highly soluble
  3. Krypton gets its name from the Greek word “Kryptos”, which means “the hidden one.”
  4. Neon signs only contain pure neon if they are orange, otherwise they contain other gases
  5. Xenon is a more potent anesthetic than nitrous oxide and allows the patient to recover more quickly
  6. Noble gases are considered to have zero electronegativity, because of the way the term is defined

Further Reading

What are the Halogens
Learning the periodic table
Functional groups in organic chemistry

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