The p-Block Elements

Group 18 Elements

How many of you have played with the helium balloons when you were kids? Well, some of you do that even today! However, are you aware of what helium is? Why is it used in balloons? Why don’t the other group 18 elements find their use in these balloons? We will read about all this in this chapter. We will look at the physical properties, chemical properties and uses of the group 18 elements.

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Group 18 Elements

The Group 18 elements include Helium(He), Neon(Ne), Argon(Ar), Krypton(Kr), Xenon(Xe), and Radon(Rn). They are referred to as noble gases or inert gases. This means that these elements are chemically inert and do not take part in any reaction.

Electronic Configuration of Group 18 Elements

The general configuration of the valence shell is ns2np6. The exception to this is helium. It has the configuration of 1s2. As they have the octet configuration in their valence shells already, they are quite chemically inert. they have the valency of zero.

The Occurrence of These Elements

All of these elements occur in a free state in the atmosphere. Apart from Radon, every other noble gas exists in the atmosphere. Argon alone constitutes 0.93% of the total atmosphere. We can prepare this element by the fractional distillation of liquid air. We can find neon, helium and argon in certain water springs as disintegrated gasses. Also, we can obtain Radon by the decay of radium and thorium minerals.

group 18 elements

(Source: io9.gizmodo)

Trends in the Atomic Properties

  • Atomic Radius: The nuclear radii increment on moving down the group with increasing nuclear number. This is a result of the expansion of another shell at each progressive element on moving down the group.
  • Electron Gain Enthalpy: Group 18 elements exhibit very stable electronic configurations. They do not have any tendency to accept an electron.
  • Ionisation Potential: They have high ionisation potentials, thanks to their closed electronic configurations. This value decreases on moving down the group due to an expansion in the nuclear size.

Physical Properties

  • Because of their stable nature, we find these elements as monatomic gases in a free state.
  • They are colourless, tasteless and odourless gases. The particles of these elements have weak Van der Waals forces. This force increases on moving down the group. This is due to an expansion in the polarising capacity of the molecules.
  • They exhibit low melting and boiling points. We can attribute this to the weak Van der Waals forces. The melting and boiling points increase as we move down the group.
  • We can condense these elements at extremely low temperatures. As the size of the atoms increases down the group, the ease of liquefaction also increases.

Chemical Properties

  • These elements are chemically latent because of their stable electronic configuration.
  • Group 18 elements have high positive electron gain enthalpy and high ionization enthalpy.
  • In 1962, Neil Bartlett anticipated that xenon ought to react with platinum hexafluoride. He was the first to set up a compound of xenon, called xenon hexafluoroplatinate(V). Later, many compounds of xenon were integrated, including fluorides, oxyfluorides, and oxides.

Xe       +                             PtF6                 →                                  Xe[PtF6]
Xenon            Platinum Hexafluoride                 Xenon Hexafluoroplatinate(V)

  • The chemical movement of group eighteen elements increments with a diminishment in the ionization enthalpy on moving down the group.
  • The ionization enthalpies of helium, argon, and neon are too high for them to shape compounds.
  • Krypton only forms krypton difluoride, since its ionization enthalpy is marginally higher than that of xenon.
  • Although radon has less ionization enthalpy than xenon, it shapes just a few compounds like radon difluoride, and a few complexes, since radon has no steady isotopes. In any case, xenon shapes an especially more prominent number of compounds.

Uses of Helium

  • Helium finds its use in filing air balloons and aircraft. This is because it is flammable and has a very low density. Because it has a very low boiling point of only 4.2 K, we use fluid helium as a cryogenic agent to perform tests at extremely low temperatures.
  • Liquid helium is common in the process of cryoscopy that we need for superconductivity. Fluid helium is a common ingredient to cool the superconducting magnets in the atomic magnetic resonance spectrometers.
  • We also use it as the cooling gas in gas-cooled atomic reactors, and also as a stream gas in gas-fluid chromatography.
  • It is also a major component in the oxygen cylinders that we use in deep sea diving.

Solved Example for You

Q: Give some uses of Neon, Argon, Krypton and Xenon.

Ans: The various uses of Neon, Argon, Krypton and Xenon include:

  • We use Neon in minute amounts in various release tubes and fluorescent light bulbs. It gives the reddish-orange shine to these bulbs and the “Neon signs”.
  • We use argon in various metallurgical processes like welding stainless steel, aluminium etc. Also, we use it for giving a stable atmosphere in research centres.
  • We use Krypton in fibre lights and release tubes. On the other hand, we use Xenon in release tubes to deliver the rapid flash that is essential for photography.
  • Radon finds its use in the treatment of cancer.
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