Group 18 (noble gases) is located at the far right of the Periodic Table of elements and is simply referred to as "inert gases" because they are extremely non - reactive due to their filled valence shells (octets). Compared to other element groups, the noble gasses were characterized relatively late.
In the late 18th century, Henry Cavendish was the first person to discover noble gases. By chemically removing all oxygen and nitrogen from an air container, Cavendish distinguished these elements. Nitrogen was oxidized to NO2 through electrical discharges and absorbed through a solution of sodium hydroxide. The remaining oxygen was removed with an absorber from the mixture. The experiment uncovered that in the receptacle, 1/120 of the volume of gas remained unreacted. William Francis (1855-1925) was the second person to isolate them, but not typify them. Francis noted the gas formation while uranium minerals were dissolved in acid.
John William Strutt discovered in the year 1894 that pure nitrogen obtained chemically was less dense than air-sampled nitrogen. He concluded from this breakthrough that there was another unknown gas in the air. With the help of William Ramsay, in his original experiment, Strutt succeeded in replicating and modifying Cavendish's experiment to better understand the inert component of air. The researchers ' procedure was different from the Cavendish procedure: by reacting with copper, they removed oxygen and removed nitrogen in a magnesium reaction. The remaining gas was properly typified and the new element was named "argon," which stands for "inert" and comes from the Greek word.
Helium was first found in the year 1868 as a bright yellow line with a wavelength of 587.49 nanometers in the solar spectrum. Pierre Jansen made this discovery. Initially, Jansen assumed it to be a sodium line. Sir William Ramsay's later studies, however, confirmed that his experiment's bright yellow line matched with that in the sun's spectrum. William Crookes, a British physicist, recognized the element as helium.
Neon, Krypton, Xenon
Morris W. Travers and Sir William Ramsay discovered these three noble gases in the year 1898. Ramsay found neon by chilling an air sample into a liquid phase, heating the liquid, and capturing the gases as they boiled off. In this process, Krypton and xenon were also discovered.
Friedrich Earns Dorn discovered the last gas in Group 18: Radon in the year 1900 while studying the decline chain of radium. In his experiments, Dorn discovered that radium compounds emitted radioactive gas. This gas was originally called niton for shining, "nitens" named after the Latin word. The International Chemical Elements Committee and IUPAC decided to name the radon element in 1923. All of the radon isotopes are radioactive. Radon-222 has the longest half-life of 4 days and is a Radium-226 alpha-decay product.
The Occurrence of These Elements
All these elements are present in the atmosphere in a free state. Besides Radon, there is every other noble gas in the atmosphere. Argon alone represents 0.93% of the overall atmosphere. By fractional distillation of liquid air, we can prepare this element. In some water springs, we can find neon, helium and argon as disintegrated gases. We can also obtain Radon by declining minerals of radium and thorium.
The Electron Configurations for Noble Gases
Neon: He 2s2 2p6
Argon: Ne 3s2 3p6
Krypton: Ar 3d10 4s2 4p6
Xenon: Kr 4d10 5s2 5p6
Radon: Xe 4f14 5d10 6s2 6p6
The Atomic and Physical Properties
In the periodic table, atomic mass, boiling point, and atomic radii increase in a group.
The first energy of ionization decreases in the periodic table down a group.
The noble gases have the largest energies of ionization that reflect their chemical inertia. Down Group 18, atomic radius and inter-atomic forces increase resulting in an increased melting point, boiling point and vaporization enthalpy.
The group density increase is correlated with the atomic mass increase. Because the atoms increase in atomic size down the group, these non - polar atoms' electron clouds become increasingly polarized, resulting in weak van Der Waals forces among the atoms. For these heavier elements, the formation of liquids and solids is, therefore, easier to achieve due to their melting and boiling points.
Because the outer shells of noble gases are full, they are extremely stable, tending not to form chemical bonds and tend to gain or lose electrons in a small way.
All members of the noble gas group act similarly under standard conditions.
Under standard conditions, all are monotomical gases. Noble gas atoms, like atoms in other groups, constantly increase in atomic radius from one period to the next due to the increasing number of electrons.
The atom size is positively correlated with several noble gas properties.
The ionization potential decreases with an increasing radius since the valence electrons in the larger noble gases are further away from the nucleus; therefore the atom holds them less tightly.
The attractive force increases with the size of the atom as a consequence of a polarizability increase and thus a decrease in the ionization potential.
Overall, noble gases have weak inter-atomic forces, resulting in very low boiling and melting points as compared to other group elements.
Heat capacity arises from possible translation, rotational, and vibrational motions for covalently bonded diatomic and polyatomic gases. Since monatomic gases do not have bonds, they cannot absorb heat as bond vibrations. Because the centre of mass of monatomic gases is at the nucleus of the atom and the mass of the electrons is at the minimal as compared to the nucleus, the rotational kinetic energy is at the minimal as compared to the kinetic energy of translation. Therefore, a monatomic noble gas's internal energy per mole is equal to its translational contribution, 32RT, where RR is the universal gas constant and TT is the absolute temperature.
Due to their stable electronic configuration, these elements are chemically latent.
Group 18 elements have a highly positive enthalpy of electron gain and high enthalpy of ionization.
Neil Bartlett anticipated in 1962 that xenon should react with hexafluoride from platinum. He was the first to establish a xenon compound called xenon hexafluoroplatinate (V). Later, many xenon compounds, including fluorides, oxyfluorides, and oxides, were integrated.
Xe + PtF6 → XePtF6
Xenon Platinum Hexafluoride Xenon Hexafluoroplatinate(V)
Group 18 elements' chemical movement increases with a decrease in the ionization enthalpy as the group moves down.
Helium, argon, and neon ionization enthalpies are too high to shape compounds.
Krypton forms only krypton difluoride, as its enthalpy of ionization is slightly higher than that of xenon.
Although radon has less enthalpy of ionization than xenon, it forms only a few compounds such as radon difluoride and a few complexes, as radon has no steady isotopes. In any case, xenon forms a more notable number of compounds in particular.
Applications of Noble Gases
Due to its low solubility in liquids or lipids, helium is used as a component of breathing gases.
Helium and Argon are used from the atmosphere to shield welding arcs and surrounding base metal.
Helium is used in cryogenics at very low temperatures, especially to keep the superconductors at very low temperatures.
In gas chromatography, helium is also the most common carrier gas.
Various common applications of Neon includes neon lights, fog lights, television cine scopes, lasers, voltage detectors, luminous warnings, and advertising panels.
Neon tubing used in advertising and elaborate decorations is the most popular application of neon.
Argon has many applications in the manufacture of electronics, lighting, glass and metal.
Argon is used in electronics to provide ultra-pure silicon crystal semiconductors and to grow germanium with a protective heat transfer medium.
Argon can also fill fluorescent and incandescent bulbs, creating the "neon lamps" blue light.
Argon also produces an inert gas shield during welding, flushes melted metals to remove casting porosity, and provides oxygen and nitrogen-free environment for glazing and rolling metals and alloys.
Krypton is sometimes selected over argon for insulation due to its superior thermal efficiency.
Krypton finds a place in fuel sources, lasers and headlights. It works as a control for a desired optical wavelength in lasers.
The production of excimer lasers is usually mixed with a halogen (most likely fluorine).
Krypton is used for high-performance light bulbs with higher colour temperatures and efficiency because Krypton lowers the filament's evaporation rate.
Xenon has different applications for incandescent lighting, development of x-rays, plasma display panels and more.
Xenon also enables better x-rays with reduced radiation levels.
When mixed with oxygen, the contrast in Plasma display panels can be enhanced by using xenon as it can replace the large picture tubes on TV and computer screens.
After cigarette smoking, radon is reported as the second most common cause of lung cancer. However, it also has beneficial usage as it is used in radiotherapy, treatment for arthritis, and bathing applications.
In radiotherapy, radon was used primarily for the treatment of cancers.
Radon exposure has been said to mitigate autoimmune diseases like arthritis.
A Quick Review:
Belonging to the farther right of the Periodic Table, Group 18 elements also known as noble gases are stable and non-reactive due to their filled octets. Henry Cavendish in the late 18th Century chemically removed oxygen and nitrogen from an air container and distinguished the noble gases. Later discoveries in the field were made by Willian Francis who was the next person to isolate these elements.
Argon was discovered by John William Strutt in 1984 through his experiments on pure nitrogen. It took three scientists to discover and identify helium, first identified as a bright yellow line. Similar discoveries were made for neon, krypton and xenon. Radon was the last gas to be discovered in 1900.
In the atmosphere, all noble gases except radon are present in a free state. Radon however can be obtained from the minerals of radium and thorium.