Noble gases are inert important factor that determines a negligible propensity to create chemicals compounds. In chemical terms, the noble gases are non-reactive, tasteless and non-flammable gases .Noble gases are the most highly ionized gases. Their atomic structure is almost perfect under standard conditions. This property has given these gases the potential to provide clues about intermolecular forces. The Lennard-Jones potential, which was first discovered in 1924, allowed scientists to calculate intermolecular forces from first principles. Noble gases may be broken down into two categories: those with a higher molecular weight and those with a lower one. The heavier ones are well understood, while the lighter ones are in their early stages of discovery. A few examples of these elements include helium and neon (Kipfer, Peeters & Stute, 2002).
1. What are noble gases?
In the periodic table, group 18 is composed of non-metallic elements that do not undergo chemical reactions. These elements are chemically inert and have eight electrons in their outermost shell. In fact, some of these elements are found in abundance in nature. The atomic masses of these elements are also large, making them monatomic gases under standard conditions. Noble gases are relatively rare on Earth, only making up a small fraction of the Earth’s atmosphere (Sano & Marty, 2013).
1.1. Abundance
Their abundance decreases as their atomic numbers increase. The most common member of the group is helium, which is the second most abundant element in the universe, accounting for a mass fraction of about 24%.The abundance of inert gases in the atmosphere varies from 5.2 parts per million (Helium) to 0.086 parts per million (Xenon). Due to their low concentrations, it is difficult to purify inert gases for industrial use. Almost always, fractional distillation is required to attain purity.
1.2. Stable molecular ions
Noble gases can also form stable molecular ions in the gas phase. The first of these was the helium hydride molecular ion, which is a combination of helium and hydrogen. Helium hydride is believed to occur naturally in the interstellar medium. Other noble gas compounds, such as the difluoroohexafluoroethane (HFE) ion, can be used in excimer lasers.
Figure 1: Noble gases
2. Elements belonging to the group of noble gases
Elements belonging to the group of noble gases are non-combustible elements with weak interatomic forces. These include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn) (Pizarro, et al., 2015).
2.1. Helium
Since the sun is the source of its namesake, the Greek word helios is where the term “helium” originates. Its high valence electron count makes it inert. The vast majority of the helium in the galaxy was created in the first few seconds of the Big Bang. However, the amount of helium in the universe has been steadily increasing due to stellar nucleosynthesis and alpha decay of heavy elements. Helium has risen to the position of third most common noble gas in the current stratosphere. Helium exerts a cytotoxic effect on cancer cells. It is also less dense than air. This means that a helium-oxygen mixture is less likely to produce turbulence. Thus, it is a potentially useful airway treatment.
2.2. Neon
In the periodic table, neon is located at position 10, and its symbol is Ne. It is an inert, colorless, and odorless noble gas with a density two-thirds of that of air. This element is the second lightest element after Helium. It is found naturally in the atmosphere to a concentration of about one part in 65,000 air. Neon is a common material for fluorescent lighting. The term “neon,” which meaning “new” in Greek, is whence we get the word “neon.” Neon has two isotopes, neon-22 and neon-20, and is found in varying amounts in moon rocks. Scientists have determined that the ratio between the two isotopes depends on the depth of the rock. Generally, a higher ratio of neon-22 is present in deeper layers of the moon rock, which indicates a higher level of solar activity.
2.3. Argon
One of the so-called “noble gases” is argon. Since argon fills neon atoms, the electrons in their most distant orbits get excited and leap to a higher energy level. This enables the atoms to emit photons, which are massless packets of light. It does not change colour or smell when exposed to air and has no chemical reactions with other chemicals. The atoms of argon do not react with oxygen, carbon, or nitrogen, and they do not form compounds. This makes argon ideal as a shield against atmospheric contamination and promotes good arc starting and arc stability. Argon is present in the atmosphere at low concentrations. It does not affect aquatic life and does not deplete the ozone layer.
2.4. Krypton
Krypton, with atomic number 36 with sign Kr, is one of the scientific elements. It is non-toxic, colorless, and odorless, Krypton is produced by the slow neutron fission of uranium. Its most stable isotope is called Kripron-85. Its low abundance in the atmosphere makes it a valuable commodity. It is extracted from the atmosphere each year in about 8 tonnes of liquid air. British chemists William Ramsey and William Ramsay discovered krypton in 1898 in a residue of evaporating liquid air.
2.5. Xenon
Xenon is an element that has characteristics that distinguish it from other noble gases. It has a full outer shell and an oxidation state of 0. It is therefore very stable and inert. Rarely do noble gases combine with other elements to create compounds. Unlike some other noble gases, xenon is relatively small and can form compounds more easily than other noble gases. Moreover, it has a low reactivity and a very narrow liquid and gaseous range. Xenon has a viscosity and density approximately three times greater than air, and it has a slower sound speed than air. This property of xenon makes it useful in reducing resonant frequencies in the vocal tract. This can result in a decreased voice pitch or in a high-pitched voice, respectively.
2.6. Radon
Radon is a radioactive gas that is found in natural gas. It is a carcinogen and can cause lung cancer in humans. The highest concentrations are found in homes built over uranium mineral deposits. It is one of the heaviest gases known. It poses a health risk due to its radioactivity while being chemically inert. Scientists have long suspected that radon was a potential health hazard because it has no known biological purpose. Only when it reacts with other substances does it become toxic. Radon is always present in the environment. The radioactivity of uranium-226 that can be encountered in common rocks like limestone is the process that produces it. In addition, the air itself contains very low concentrations of it. Its discovery is credited to a German physicist, Friedrich Ernst Dorn.
3. Characteristics of inert gases
Noble gases are elements that have unusual properties. They are inert to the body. They also exhibit unique properties, which are of interest to chemists. The chemical properties of noble gases vary greatly. Some can be used to create explosives and compounds in the laboratory. These elements are rarely found naturally bonded to other elements. fAs these gases have minimal or no chemical reactivity. They are odorless (Kipfer, Peeters & Stute, 2002).
3.1. Colorless
Noble gases are colorless in their elemental state, but can ’emit’ color if they are charged. Unlike ordinary gases, noble gases cannot react with other elements or form large molecules or clusters. They simply ’emit’ color when they are in high energy states, but fall back to their original state of non-reactivity.
3.2. Ionization enthalpy
Elements belonging to the group of noble gases exhibit a high ionization enthalpy, a measure of their reactivity. Elements in this family contain eight valence electrons in their outermost orbit. In spite to this, individuals of the group exhibit significant increases in their electron gain enthalpies. However, as the atomic size of the elements increases, their ionization enthalpies decrease.
3.3. Low electronegativities
A compound’s electronegativity may be thought of as a measurement of the degree of charge that is transmitted together with the energy that goes along with it. The electronegativity of an element is determined by dividing its charge distribution by the number of electrons in its valence shell. Elements in the group of noble gases exhibit low electronegativities.
3.4. Low boiling point and boiling point
The name “noble gases” is used to describe a group of elements with low boiling points and melting points. These substances have no natural chemical bonds and are thus often used in laboratory experiments. In addition to this, they are very uncommon, accounting for just a tiny portion of the atmosphere around the Earth. Both the gelatinization and freezing temperatures of elements that are part of the category of noble gases are rather low. This is due to weak electrical attractive forces. When considering high – temperature as well as freezing degrees, remember that these values rise with the atomic numbers. The atomic radii also increase.
3.5. Multiple stable isotopes
Noble gases have multiple stable isotopes and can be used in geochemical tracers to investigate their origin and residence time. The study of palaeo groundwater that existed before the Holocene may benefit greatly from their utilization. These gases have been found in fluids of deep crustal origin, including the Witwatersrand Basin in South Africa and the Great Artesian Basin in Australia.
3.6. Reactivity
The noble gases are gases with high valence shells that are relatively unreactive. Their low electronegativities and high ionization energies mean that they rarely react with each other. The exception is Xenon, which shows a moderate amount of reactivity and can form complexes. It is the last noble gas to be isolated, which led to its nickname, ‘the stranger’.
4. Use and applications of noble gases
There are several reasons why noble gases are used. One is their high stability. Because they are so stable, they do not undergo unwanted chemical reactions. They feature complete valence electron shells, which contributes to their high degree of stability. Similarly their inert properties make them suitable for a variety of application. Examples of such applications include lasers, neon lights, krypton headlights and superconducting magnets. Deep-sea divers use a mixture of helium and oxygen for their breathing gas (Sano & Marty, 2013; Pizarro, et al., 2015).
4.1. Manufacturing processes
Inert gases are used in inert atmospheres and they can also be used to cool superconducting magnets their low density makes them ideal for room-temperature applications. Many industries and processes make use of inert gases in their manufacturing processes, such as welding, where they can create a cleaner weld and reduce contamination.
4.2. CT imaging and incandescent lighting
Xenon is used in many industries, including nuclear medicine and incandescent lighting. It is also used to increase contrast in CT imaging and has made it possible to obtain better x-rays with less radiation. It has also been used in plasma display which may someday replace large picture tubes Xenon has many applications in science and technology. Another use for this inert gas is in the health care industry.
4.3. Superconducting devices
Liquid helium is a key component of particle accelerators, as it can be used to cool superconducting devices at low temperatures. Several facilities in the U.S., as well as the European Large Hadron Collider, use this substance for cooling. In these accelerators, helium is used to cool sensitive instruments and to eliminate mechanical and electrical noise. Additionally, helium is used as a coolant in pebble-bed reactors.
4.4. Electromagnetic calorimeters
Krypton is also used in the construction of quasi-homogeneous electromagnetic calorimeters, including the NA48 particle-physics experiment at CERN. It is also used in medicine to detect abnormal openings in the heart. Liquid krypton is an uncommon and expensive substance, but its small Moliere radius makes it an ideal choice for these applications. Also, the shorter Moliere radius allows for more precise spatial measurements and less overlapping patterns.
4.5. Lighting applications
Liquid krypton is also used as a light source. In the presence of an electromagnetic flow, it emits a dazzling white illumination. This property makes it a desirable gas for lighting applications, including neon signs, runway lights, and flashbulbs. It is also used to make fluorescent and energy-efficient fluorescent lamps.
4.6. Heat transfer medium
Noble gases have many uses. The primary one is as a heat transfer medium. These materials are ideal for use in high-end heating systems. Liquid radon is one such application. It can also be used in lasers, discharge tubes, and fluorescent tubes.
4.7. Vocal tract
Inert gases with the features of helium-xenon are valuable for diagnostic scanning due to their unique characteristics. Xenon has a viscosity and density approximately three times greater than air, and it has a slower sound speed than air. This property of xenon makes it useful in reducing resonant frequencies in the vocal tract. This can result in a decreased voice pitch or in a high-pitched voice, respectively.
Conclusion
Noble gases are substances that are derived from air. Helium is a naturally occurring gas. It is used in balloons, replacing hydrogen. Its protective properties have been studied in animals, including humans. However, the mechanisms behind these noble gases’ action are unknown. In the past, these elements were referred to as inert because their atoms could not form compounds with other elements. Since they are inert, they are chemically inert and are non-reactive. However, their chemical properties have only recently been discovered. Noble gases are thought to have a low ionization potential. They are also monatomic under standard conditions.
References
1. Kipfer, R., Aeschbach-Hertig, W., Peeters, F., & Stute, M. (2002). Noble gases in lakes and ground waters. Reviews in mineralogy and geochemistry, 47(1), 615-700.
2. Sano, Y., Marty, B., & Burnard, P. (2013). Noble gases in the atmosphere. In The noble gases as geochemical tracers (pp. 17-31). Springer, Berlin, Heidelberg.
3. Suárez-Iglesias, O., Medina, I., Sanz, M. D. L. A., Pizarro, C., & Bueno, J. L. (2015). Self-diffusion in molecular fluids and noble gases: available data. Journal of Chemical & Engineering Data, 60(10), 2757-2817.