18th group or Zero group in the periodic table contains six elements Helium(He), Neon(Ne), Argon(Ar), Krypton (Kr), Xenon (Xe), Radon (Rn). These collectively called inactive or inert gases because they have very no reactivity or very less reactivity at normal temperatures. The Zero group compounds are also known noble gases because some of the compounds of these gases are isolated under certain specific conditions only.
Electronic Configuration of Noble Gases
Noble gas has fully filled electronic configuration that mean they don’t need to lose or gain an electron. In outermost shell these gases have 8 electrons except Helium which have 2 electrons in its outer shell.
The occurrence of Noble Gases: –
Noble gases occur in Free State because of their inert nature. Except Radon (Rn) all the Noble gases are found in the atmosphere in the atomic state. Helium present in the atmosphere in traces of about 0.000524%. Helium also presents in natural gas to the extent of 2~7 %. Radon is a naturally occurring radioactive element.
1.Most abundant Noble gas in the universe
If someone asking about the most abundant noble gas in the universe then answer is Ar gas because The composition of the element that makes the whole universe as below
~ 76 %
~ 23 %
Hydrogen gas is the most abundant element in the universe about 76 % of the mass of the whole universe is made of Hydrogen gas. Helium is the second most abundant element of the universe as it makes about 23% of the mass of the whole universe. Other elements combined form the remaining 1% of the mass of the whole universe.
2.Most abundant Noble gas in the Earth’s Atmosphere
The earth’s atmosphere mainly composed of nitrogen (78%), Oxygen(21%),and Argon (0.9%) and remaining of the traces of all other gases such as Carbon dioxide(CO2),Neon(Ne),Helium(He),Methane(CH4),NitrousOxide,Krypton(Kr), Hydrogen(H2), Ozone(O3) etc.
Carbon dioxide (0.03%)
It shows that Nitrogen and Oxygen are the biggest components of Earth’s atmosphere and Argon is the third most abundant element in the atmosphere about 0.9%. The other two noble gases in the earth’s atmosphere take up only 0.1% of all the trace gases Helium(~0.00052%) and Neon(0.00182%), This shows that Argon is the most abundant noble gas in Earth’s atmosphere
Isolation of Noble Gases:-
Isolation of Helium (He)
He can be isolated from the atmosphere by fractional distillation of liquefied air in the same way the other Noble gases (Ne, Ar, Kr, Xe) are obtained. But it is commercially isolated from the natural gas reservoir deep under the earth’s crust.
Natural gases are compressed to about 100 atm and cooled at 73K where all other components liquefied but Helium (He) remains in gaseous form. By this technique, up to 99% pure Helium gas can be obtained.
Helium can also be produced by heating monazite sand at 1000 0C.
Isolation of Ne, Ar, Kr, Xe:-
These gases are produced by the fractional distillation of liquefied air. It gives a mixture of Noble gases, Oxygen (O2), Nitrogen (N2). These individual gases are further obtained by adsorption of air on coconut charcoal. Charcoal adsorbs different gases at different temperatures.
Isolation of Radon (Rn):
Radon is a naturally occurring element which can be obtained by radioactive decay of Radium
88Ra226 ——-> 86Rn222+ 2He4
Properties of Noble Gases:
Size of Noble gases:
The atomic radii of noble gases correspond to the Vander Waal’s radii. The size of noble gases down the group increases as atomic radii increase.
B.P. and M.P. of Noble Gases: –
Ongoing down the group B.P. & M.P. of noble gases are increasing due to Vander Waal’s attraction force. Chemical Reactivity of Noble Gases: Noble gases have completed octet in case Hydrogen duplete and don’t have a tendency to exchange electrons.
therefore noble gases are inactive however only He is completely inactive, other noble gases have low reactivity when they provide enough energy. Higher member of noble gases forms some compounds like XeO2, XeF6, etc.
Polarizability of Noble Gases:
The polarizability of the noble gases increases down the group as the size increases.
Ionization Energy and Electron Affinity of Noble Gases:-
The noble gases possess stable fully field electronic configuration. They don’t have the tendency to gain or loss of electron as they have fully filled octet or duplet in their outermost shell. Therefore, noble gases have high ionization energy and zero electron Affinity.
The solubility of Noble gases in water:
The inert gases are slightly soluble in water however solubility in water increased down the group with increasing atomic number.
The heat of vaporization of Noble Gases:
The heat of vaporization of noble gases is low as these are bonded with very weak Vander Waal’s forces between their monoatomic molecules. However, the value of vaporization increases down the group. This because of an increase in polarizability of a large electronic cloud of the element with a higher atomic number.
Liquefaction of Inert Gases:
It is difficult to liquefy the inert gas as their atoms are bonded by weak Vander Waal’s forces. The ease of liquefaction increases down the group. He has the lowest B.P (4.18K) of any known substance
Uses of Noble Gases In Daily Life
Helium is lighter than air and inert in nature hence it is used floating balloons.
Helium is used for diluting the pure oxygen in deep seas diving cylinder because it has less solubility in blood
Argon is used in common light bulbs also in the welding arc
Neon glows bright red when electricity is passed through it hence it is used in sign tubing in adverting sector
Krypton and Xenon have wide application in photographic flash