The name makes an analogy to the term "noble metals", such as gold which were associated with wealth and nobility and also have low reactivity. The noble gases have also been referred to as inert gases, but this label is now deprecated as many noble gas compounds are known. Rare gas is another term that was used, but this is also inaccurate because argon forms a fairly considerable part of Earths atmosphere.
In fact the noble gas molecule consists of a single atom rather tha two atoms like N2 and O2. In addition for many years no one could find any examples of a noble gas forming compounds with other elements either in nature or in the laboratory.
The noble gases are a group of six chemical elements - helium, argon, neon, xenon, krypton and radon in the last column of the periodic table. When all the noble gases were identifies, around one hundred years ago, chemists thought that they were very unusual. The noble gases could not be made to react with other chemicals, so they did not have many uses.
Noble gases can form endohedral fullerene compounds, in which the noble gas atom is trapped inside a fullerene molecule. In 1993, it was discovered that C60 a spherical molecule consisting of 60 carbon atoms is exposed to noble gases at high pressure.
The method of simplifying the electron distribution to the orbitals is called the noble gas notation. It is the representation of all of the lower filled orbitals up to the closest noble gas by enclosing its symbols in brackets. The remaining orbitals are written in the usual way.
For example, cobalt is found in the fourth period of the table. The full notation is 1s2
. Counting back to the previous noble gas, argon gives the noble gas configuration [Ar]2s2
Helium is also used in weather balloons and airships in the place of H2. Radon is useful in the treatment of cancer because it is radioactive in nature. Argon provides inert atmosphere for metallurgy. Neon is used in neon discharge tubes which gives familiar reddish orange yellow glow of neon signs. Krypton and xenon are used in filling incandescent metal filament electrical bulbs as these gases are found superior to argon for this purpose.
In recent years the use of heavy noble gases has become more and more economically feasible as these gases provide a considerable improvement of thermal insulation with respect to Ar.
The noble gases constitute group 18 in the periodic table. This group had no place in the original periodic table of Mandeleev as these were unknown. Mendeleev even did not provide blank spaces for them as he could not suspect the existence of elements totally devoid of chemical activity.
Because of chemical inertness of these gases, these were assigned zero valency and the group in which they were place was designated as zero group. The place of noble gas in periodic table is shown below.
The noble gases are generally inert and do not participate in the reactions easily. The inertness of noble gases is due to the following reasons. Valance electrons involve in the formation of chemical bonds and also in chemical reactions. So we can say that they play an important role in any element.
- The atoms of noble gases have stable closed shell electronic configuration.
- The noble gases have very low electron affinities,
- The noble gases have exceptionally high ionization energies.
The valence shell electronic configuration for He is 1s2
and for other inert gases it is ns2
. In these configurations, the sub-shells belonging to valence shell are fully filled and hence the configurations of inert gases are quite stable. Therefore, atoms of these elements have no tendency to lose or gain electrons and thus do not participate in reactions under normal conditions. The stable electronic configurations of noble gases are responsible for their inert behavior.
|1 ||Helium ||H ||2||1s2 |
|6 ||Radon ||Rn ||86||[Xe] 4f145d106s26p6|