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Group 18: Physical And Chemical Properties

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Group 18: Physical And Chemical Properties - Lesson Summary

Physical properties:

You know that the elements of group eighteen have closed shell structures, because of which they have no tendency to form compounds under normal conditions.

Due to their inert nature, these elements exist in free State as monatomic gases.

These elements are colourless, tasteless and odourless gases.

They are sparingly soluble in water.

The atoms are held by the weak Van der Waals forces .These forces also called London dispersion forces.

The magnitude of Van der Waals forces increases on moving down the group with an increase in the polarisability of the atoms.

The melting and boiling points of these elements are very low. This is, due to the weak Van der Waals forces of attraction.

The melting and boiling points increase on descending the group with an increase in the magnitude of the Van der Waals forces of attraction.

Due to the weak Van der Waals forces, noble gases can be liquefied at very low temperatures. With an increase in the magnitude of the Van der Waals forces down the group, the ease of liquefaction of noble gases also increases.

Helium has the lowest boiling point among all the elements in group eighteen

Chemical properties:

These elements are chemically inert due to their stable electronic configuration.

These elements have high ionisation enthalpy and higher positive electron gain enthalpy.

In 1962, Neil Bartlett predicted that xenon should react with platinum hexafluoride. He was the first to prepare a compound of xenon, called xenon hexafluoridoplatinate (V).

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

Later, many compounds of xenon were synthesised, including fluorides, oxides and oxyfluorides.

The chemical activity of group eighteen elements increases with a decrease in the ionisation enthalpy on descending the group.

The ionisation enthalpies of helium, neon and argon are too high for them to form compounds.

Krypton forms only krypton difluoride, since its ionisation enthalpy is slightly higher than that of xenon.

Even though radon has less ionisation enthalpy than xenon, it forms only some compounds like radon difluoride, and some complexes, since radon has no stable isotopes. However, xenon forms a markedly greater number of compounds.


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