What are Noble Gases?

Noble gas or inert gas or rare gases is referred to six naturally occurring colourless, odourless monoatomic chemical elements placed in Group 18 or Group VIIIA in the periodic table. These six naturally occurring noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Oganesson (Og), is also placed with the noble gas family but its chemistry is under investigation.

Noble gas or inert gas referred to six naturally occurring chemical elements of Group 18 or Group VIIIA in periodic table uses mainly in fluorescent lamps

All the noble gases have very low reactivity due to their filled valence shell electronic configuration and very high ionization energy. The lack of chemical reactivity of the noble gases is the reason to call them inert.

Atomic number Noble gas Symbol Electronic configuration
2 Helium He 1s2
10 Neon Ne [He] 2s22p6
18 Argon Ar [Ne] 3s23p6
36 Krypton Kr [Ar] 3d104s24p6
54 Xenon Xe [Kr] 4d105s25p6
86 Radon Rn [Xe] 4f145d106s26p6
118 Oganesson Os [Rn] 5f146d107s27p6

The closed-shell electronic configuration developed very little intermolecular attraction. Therefore, they possess very low boiling and melting points.

Radon is a radioactive noble gas obtained by the radioactive decay of uranium mines. The gases, neon argon, krypton, xenon, and radon formed a face-centered cubic crystal lattice. Only helium formed a close-packed hexagonal crystalline solid structure.

All the noble gases are placed in group 18 of the periodic table along with p-block elements. The physical properties and uses of all the noble gases are very similar. For example, the melting point and boiling point of noble gas a close together. Therefore, all the gases are used in fluorescent lamps for light generation.

Why are Noble Gases Unreactive?

Noble gases are unreactive due to the filled valence orbital configuration. The lack of chemical reactivity of noble gases was the reason to call them inert.

In fact, before 1962, no true compound was known. They only formed clathrates or cage compounds with water and pare quinol through the hydrogen bonding network.

Discovery of Noble Gas

The noble gas in the periodic table was discovered through its physical properties like electromagnetic spectrum and gas density. In 1785, English chemist and physicist Henry Cavendish observed that a sample of air always leaves a small residue of substance (about 1/120th part) after repeated sparking air with excess oxygen.

Who Discovered Argon?

The first discovery of noble gas was found nearly one hundred years after this observation. The fine experiment was done after a century by Sir William Ramsay, a Scottish chemist, and Lord Rayleigh, an English physicist 1894. Lord Rayleigh observed that nitrogen isolated from atmospheric gases was 0.5 percent heavier than nitrogen prepared chemically.

In 1894, chemist Sir William Ramsay identified a new element (argon meaning lazy) in the residue left after heating atmospheric nitrogen with magnesium.

Who Discovered Helium?

A yellow line was observed close to the sodium D-lines in the spectrum of sun chromophore during the total solar eclipse.

Lockyer and Frankland assigned this to a new element which they named helium (Greek helios meaning sun). The same line was observed by L Palmieri in the spectrum of volcanic gases.

Discovery of Neon, Krypton, and Xenon

Ramsay and Travers discovered three new noble gases neon, krypton, and xenon by low-temperature distillation of liquid air. Rutherford and Soddy isolate radon (a Latin word meaning ray) from the radioactive decay of minerals.

Properties of Noble Gases

Properties Helium Neon Argon Krypton Xenon Radon Oganesson
Atomic number 2 8 18 36 54 84 118
Atomic weight 4.003 20.180 39.95 83.798 131.293 [222] [294]
Density (g cm-3) 0.000164 0.000825 0.001633 0.003425 0.005366 0.009074 unknown
State at 20 °C gas gas gas gas gas gas solid
Boiling point −268.92°C −246.05°C −185.85°C −153.41°C −108.1°C −61.7°C unknown
Solubility (water) cm3/L at 20°C 8.6 10.5 34 59 108 230 unknown

The valence shell of noble gas contains complete s- and p-orbital, which is a very stable configuration. Therefore, the energy required for the promotion of an electron to the next available vacant orbital is quite large.

For example, the promotional energy for xenon is very large equal to 963 kJ mol−1. The fact suggests that covalent bonding involving sp3d or sp3d2 valence state is highly unfavorable for xenon. Ionic chemical bonding to form the compounds of the type Xe+F is similarly difficult due to high positive entropy and free energy.

For more details about noble gas, see the individual learning chemistry topics of gases like helium, neon, argon, krypton, xenon, radon, and oganesson.

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