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Properties of Noble Gases

 

The noble gases, which are elements of Group 0 of the periodic table shown certain similar properties. These elements are: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn) have electronic configuration showing all the orbitals and shells to be completely filled.

They are called the noble gases because of their lack of chemical reactivity. Before 1962 they were all thought to be incapable of forming bonds with other elements and for this reason they were known as the inert gases. In the belief that zero is the only oxidation state in which they can exist, the group made up of these elements was designated Group 0 in the periodic table. Their apparent inertness provided the key to the explanation to the chemical activity of the other elements.

Their molecules are monatomic, symmetrical and nonpolar. They have very low melting and boiling points (far below room temperature - see table below) because of the weakness of van der waals forces which hold their molecules together.

Element

Melting Point oC

Boiling Point oC

He

-272.2

-268.9

Ne

-249

-246

Ar

-189

-186

Kr

-157

-153

Xe

-112

-107

Rn

-77

-62

In 1962, Neil Bartlett discovered that xenon reacts with PtF6 to form a yellow solid believed to have the formula XePtF6. This led to the discovery that xenon could combine directly with fluorine, the most electronegative of all elements. At 400oC the two elements combine to form XeF4, which exists in the form of colorless crystals below its melting point, 90oC.

Compounds subsequently prepared include XeF2, XeF6, RnF4, and KrF4. Hydrolysis of xenon hexafluoride produces xenon trioxide:

XeF6 + 3H2O → XeO3 + 6HF

The xenon trioxide is a white crystalline solid that is highly explosive. Since the ionization energies of the noble gases become less with increasing atomic number, we may expect radon to be the most reactive member of the group, and we may expect helium to be the least reactive. Helium, neon, and probably argon will likely continue to be known as inert gases. Of the chemical elements known, these three are certainly the most inert.

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