Noble gases, also known as inert gases, rare gases, and group 18 elements, are a group of elements that have very low reactivity due to their full valence electron shells. This is one of the key properties of noble gases, which makes them very stable and unreactive. This means that they do not readily combine with other elements or form chemical bonds. The electronic configuration of the noble gases is characterized by a complete outer shell of electrons, which makes them the most stable elements in the periodic table.
Also, the low reactivity of the noble gases is due to the fact that they have a complete outer electron shell, which makes it difficult for them to lose or gain electrons. In order to react with other elements, an atom must lose, gain, or share electrons. However, the noble gases already have a full outer electron shell, so they do not need to gain, lose, or share any electrons in order to become stable. This makes them very unreactive and inert.
They were once called the rare gases because they were thought to be rare in occurrence. However, with advances in technology and the discovery of natural gas deposits, it was found that noble gases are actually quite abundant in the Earth’s atmosphere.
Members of Group 18 Elements
The group 18 or group VIII A elements of the periodic table include: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
This is a group of elements are located in the far-right side of the periodic table and have similar chemical properties due to their full valence electron shells. This contributes to their chemical inertness and their tendency to exist as monoatomic gases.
Group 18 Elements
| Element | Symbol | Electronic Configuration | Sources | Appearance / Uses |
|---|---|---|---|---|
| Helium | He | 1s2 | Natural gas wells, air, some minerals | Colorless gas, only known to form unstable compounds |
| Neon | Ne | [He] 2s2 2p6 | Air, some natural gas wells | Colorless gas, used in neon signs and gas discharge lamps |
| Argon | Ar | [Ne] 3s2 3p6 | Air, some natural gas wells | Colorless gas, used in gas-filled incandescent lamps and welding |
| Krypton | Kr | [Ar] 3d10 4s2 4p6 | Air, some natural gas wells | Colorless gas, used in some photographic flashes and lamps |
| Xenon | Xe | [Kr] 4d10 5s2 5p6 | Air, some natural gas wells | Colorless gas, used in some lamps, medical imaging, and as a general anesthetic |
| Radon | Rn | [Xe] 4f14 5d10 6s2 6p6 | Naturally occurring radioactive decay of uranium and thorium | Colorless gas, radioactive, used in some medical treatments |
Electron Configuration
The electron configuration of noble gases is characterized by a completely filled outermost electron shell. For example, neon has the electron configuration 1s2 2s2 2p6, with the 2p6 subshell being completely filled.
The valence shell electronic configuration of group 18 elements is ns2 np6 which means their octet is completed, resulting in high ionization energy and low electronegativity.
The VSEPR theory is a powerful technique used for predicting the shapes of noble gas compounds with a relatively large number of electron pairs. In the valence shell of the central atom, noble gases have filled shells.
Occurrences and Extractions of Noble Gases
Each of the noble gases (rare gases) can be found in various natural sources, and some of them can be extracted and purified for use in various applications.
Here is a closer look at the sources and extraction methods of each Group 18 element:
Helium (He)
Helium is relatively rare on Earth. It is mainly extracted from natural gas fields, where it is produced by the radioactive decay of uranium and thorium. The largest helium reserves are found in the United States, Russia, and Algeria. The extraction process involves drilling wells and separating helium from other gases using a series of cryogenic distillation processes.
Neon (Ne)
Neon is a relatively rare element on Earth and is mainly found in the atmosphere. It is extracted from the air by a process known as fractional distillation. The air is first cooled to liquefy the gases, and then they are separated based on their boiling points. Neon is used in various applications, including lighting, plasma displays, and cryogenics.
Argon (Ar)
Argon is the most abundant noble gas in the earth’s atmosphere, making up about 0.93% of the air. It is extracted from the air by fractional distillation. The air is first purified to remove moisture, carbon dioxide, and other impurities, and then it is cooled to condense the argon. Argon is used in welding, metal fabrication, and lighting.
Krypton (Kr)
Krypton is a rare element on Earth, and its concentration in the atmosphere is only about 1 ppm. It is mainly extracted from the air by fractional distillation. Krypton is used in lighting and imaging applications, as well as in high-power gas lasers.
Xenon (Xe)
Xenon is a rare element on Earth, with a concentration in the atmosphere of only about 0.08 parts per million. It is mainly extracted from natural gas fields, where it is produced by the radioactive decay of uranium and thorium. The extraction process involves drilling wells and separating xenon from other gases using a series of cryogenic distillation processes. Xenon is used in various applications, including lighting, anesthesia, and ion propulsion systems.
Radon (Rn)
Radon is a radioactive noble gas that is produced by the decay of radium in the earth’s crust. It is mainly found in underground water and rocks, and it can seep into buildings and homes through cracks and holes in the foundation. Radon is a health hazard and can cause lung cancer, so it is important to test for radon levels in homes and buildings and take measures to mitigate its presence.
Appearances of Group 18 Elements
- The noble gases are unique in that they are generally gases at standard temperature and pressure, with the exception of radon, which is a radioactive solid.
- They are also colorless, odorless, and tasteless.
- Their low reactivity and lack of toxicity make them useful in a variety of applications.
Characteristics of Noble Gases
One of the defining characteristics of noble gases is their stability. The valence electrons of noble gases are fully filled in their outermost energy level, and this leads to their exceptional stability. Helium has two valence electrons, while neon, argon, krypton, xenon, and radon have eight valence electrons each.
Due to their full valence shells, they do not easily form chemical bonds with other elements. Instead, they exist as individual atoms and are colorless and monotonic.
Boiling Point
The boiling point of noble gases increases as you go down the group, due to the increasing size and density of the atoms and the strength of London dispersion forces. In other words, the boiling points of these elements increase as well. This increase occurs because the intermolecular forces between larger atoms with more electrons are greater than those between smaller atoms with fewer electrons.
Helium has a boiling point of -270°C, while neon’s boiling point is -246°C, argon’s is -186°C, krypton’s is -153°C, xenon’s is -107°C, and radon’s is -62°C.
The density of the noble gases also increases as the atom size gets bigger. As a result, larger atoms occupy more space in a given volume, resulting in increased density.
Atomic Radius
Another property that varies across the noble gas group is the size of the atom (atomic radius). Moving down the group, the number of electron shells increases by one, causing the atoms to get larger. In other words, the atomic radius of the noble gases decreases slightly from helium to xenon, which is due to the increasing nuclear charge. However, the atomic radius of radon is larger than that of xenon due to the presence of additional electron shells.
Ionization Energy
The ionization energy of the noble gases is generally high due to their stable electronic configurations. It increases from helium to radon, as the atomic radius decreases, and the effective nuclear charge increases.
Electronegativity
The noble gases have very low electronegativities due to their stable electronic configurations. They do not easily attract electrons from other atoms, making them highly unreactive.
Electron Affinity
The electron affinity of the noble gases is zero or close to zero due to their stable electronic configurations. They do not tend to accept electrons from other atoms.
Trend Down the Group 18 of the Periodic Table
The atomic radius of the noble gases increases down the group due to the addition of a new electron shell at each succeeding element. As a result, the ionization energy decreases down the group. The electronegativity and electron affinity also decrease down the group due to the increasing atomic size and distance between the valence electrons and the nucleus.
Reactivity of Group 18 Elements
The noble gases are considered non-reactive (inert gases), but some of them can form stable compounds with highly reactive elements. For example, krypton and xenon can react with fluorine to produce compounds such as xenon tetrafluoride and xenon hexafluoride. Additionally, krypton can react with fluorine to form krypton difluoride.
Reactivity: Noble gases are generally unreactive due to their complete outermost electron shell, but can form compounds under certain conditions. For example, xenon can react with highly reactive elements such as fluorine to form stable compounds.
General Reactions of Noble Gases
Noble gases are generally unreactive due to their complete outermost electron shell, but can form compounds under certain conditions.
These general reactions of noble gases are:
Reaction with fluorine: The noble gases can react with fluorine to form noble gas fluorides.
Reaction with oxygen: The noble gases can react with oxygen to form noble gas oxides.
Reaction with chlorine: The noble gases can react with chlorine to form noble gas chlorides.
The reactions of each element in Group 18 are discussed below:
Helium (He)
Helium is chemically inert and does not readily react with other elements. It has a stable, full valence shell of electrons and does not need to gain or lose electrons to achieve stability. Therefore, it does not form any chemical compounds.
Neon (Ne)
Like helium, neon is also chemically inert and does not form compounds under normal conditions. However, under certain conditions, it can form compounds with highly electronegative elements like fluorine and oxygen. For example:
Reaction with fluorine: Ne + F2 → NeF2
Reaction with oxygen: 2Ne + O2 → 2NeO
Argon (Ar)
Argon is also chemically inert and does not readily react with other elements. However, it can form compounds with highly electronegative elements under certain conditions.
For example:
Reaction with fluorine: Ar + 3F2 → ArF6
Reaction with oxygen: Ar + 2O2 → ArO4
Krypton (Kr)
Krypton is chemically inert and does not react with other elements under normal conditions. However, it can form compounds with highly electronegative elements under certain conditions.
For example:
Reaction with fluorine: Kr + 2F2 → KrF4
Reaction with oxygen: Kr + O2 → KrO2
Xenon (Xe)
Xenon is the most reactive of the noble gases and can form compounds with a variety of elements under certain conditions.
For example:
Reaction with fluorine: Xe + 2F2 → XeF4
Reaction with oxygen: 2Xe + O2 → 2XeO3
Reaction with chlorine: Xe + Cl2 → XeCl2
Reaction with nitrogen: Xe + N2 → XeN2
Reaction with hydrogen: Xe + 2H2 → XeH4
Radon (Rn)
Radon is highly radioactive and does not have any stable isotopes. Therefore, its chemical properties have not been extensively studied. However, it is expected to be similar to other noble gases and be chemically inert.
Some Other Reactions of Noble Gas Elements
Noble gas inclusion compounds or clathrates are formed between noble gases and strongly hydrogen bonding components like water and polyphenols. Although these compounds are not actual chemical compounds, noble gas atoms occupy voids in the hydrogen-bonded lattice of the host compound. For instance, Xenon forms a clathrate with water of approximate composition even two times, with a melting point of 24oC.
Noble gas compounds, specifically fluorides, are also discussed. Most noble gas compounds are fluorides, with the majority being xenon fluorides.
Krypton difluoride is the only known halide, and it is synthesized by passing an electrical discharge through a fluorine-krypton mixture.
Xenon, on the other hand, can form three neutral fluorides, including xenon difluoride, xenon tetrafluoride, and xenon hexafluoride.
Applications of Noble Gases
Despite their low reactivity, noble gases are still useful in a variety of applications. One of the most common uses of noble gases is in lighting, where they are used to produce bright and efficient light. For example, neon is used in neon signs, while xenon is used in high-intensity discharge lamps. These lamps are used in a variety of applications, including in street lighting, car headlights, and projectors.
Noble gases are also used in welding, where they are used as an inert gas shield to protect the weld from contamination by the surrounding air. Argon is the most commonly used inert gas shield in welding, as it is relatively cheap and easy to obtain. In addition to welding, argon is also used in the production of titanium and other metals, as well as in gas lasers.
Another important application of noble gases is in gas chromatography, which is a technique used to separate and analyze mixtures of chemicals. Noble gases are used as carrier gases in gas chromatography, where they are used to transport the sample through the chromatographic column. Helium is the most commonly used carrier gas in gas chromatography, as it is inert, has a high thermal conductivity, and is readily available.
Some other applications are the use as low-temperature refrigerants and of liquid xenon as an extremely unreactive solvent. Additionally, krypton fluoride is a powerful fluorinating agent, while xenon difluoride can oxidize xenon to xenon hexafluoride and even metallic gold to gold hexafluoride anion.
However, it is important to note that one of the noble gases, radon, is radioactive and can be harmful if exposure levels are too high. Radon is a naturally occurring gas that is produced from the decay of uranium and thorium. It can accumulate in buildings and can cause health problems, including lung cancer. It is important to test homes and buildings for radon levels in order to prevent exposure.
Compounds of Group 18 Elements
These properties and reactions of various xenon fluorides, including their geometries and shapes determined by VSEPR theory.
Group 18 Halides
Xenon difluoride (XeF2) has a linear geometry, XeF4 has an octahedral geometry with a planar shape, and XeF6 has a distorted octahedral structure due to the delocalization of the lone pair of electrons over the entire octahedral geometry.
The xenon fluorides can selectively oxidize central heteroatoms of main group compounds such as arsenic and phosphorus, but not organic substrates bonded to them.
For example, the reaction involving the selective oxidation of arsine (AsH3) to form pentavalent penta-coordinated trimethyl difluoroarsine (Me3AsF2) using Xenon difluoride (XeF2), and the selective oxidation of diphenyl phosphine (Ph2PH) to form PH2PHEF2 and xenon using XeF4.
AsH3 + 2 XeF2 → Me3AsF2 + 2 Xe + 3 HF
Ph2PH + 2 XeF4 → PH2PHEF2 + 2 Xe + 2 HF
The first reaction produces pentavalent penta-coordinated trimethyl difluoroarsine, while the second reaction produces bis(difluoro-phosphino) methane and xenon gas.
Xenon difluoride can also oxidize water to oxygen, and XeF4 can oxidize platinum metal to PtF4. The passage also discusses the extensive chemistry of noble gas fluorides and their reactions with fluoride ion donors and acceptors.
Noble gas fluorides can react with strong fluoride ion acceptors such as group 15 pentafluoride derivatives of arsenic, bismuth, tantalum, ruthenium, and platinum. Xenon difluoride forms the greatest number of compounds through this type of reaction, followed by XeF6, XeF4, and KrF2.
The formation and properties of xenon-oxygen compounds, which are formed from the hydrolysis of xenon fluorides such as XeF4 and XeF6. The resulting compounds have xenon in various oxidation states, including +6 and +8.
There are various reactions involving xenon-oxygen compounds, such as the hydrolysis of XeF4 to form xenon oxide and six HF, and the reaction of XeF6 with water to form xenon oxyfluoride and two HF.
Also the substitution of fluoride in xenon fluorides to form xenon-oxygen compounds, as well as reactions with oxy acids to eliminate HF. Examples of such reactions are given, such as the reaction of XeF with XOH to form FXeOH and HF.
The bridging halides in the compounds are written at an angle, closer to the tetrahedral angle because each bridging di-bridging halide ion has two lone pairs intact on it.
Various geometries and shapes of xenon fluorides can be determined using VSEPR theory. For example, XeF2 has a linear geometry, XeF4 has an octahedral geometry with a planar shape, and XeF6 has a distorted octahedral structure due to the delocalization of the lone pair of electrons over the entire octahedral geometry.
Among the noble gases, xenon is the most chemically active due to the presence of the outermost electrons in its valence shell. Xenon compounds with oxygen, nitrogen, chlorine, and carbon are known and they can be synthesized by a variety of methods. One of the common methods is hydrolysis, which is a reaction between a compound and water.
Reaction of Halides with Water
When xenon compounds react with water, they form oxyfluorides, which contain bonds between xenon, fluorine, and oxygen. These oxyfluorides are stable and have several applications in industries such as electronics, aerospace, and chemical manufacturing.
For instance, when xenon hexafluoride (XeF6) reacts with water, it forms xenon oxytetrafluoride (XeOF4) and hydrofluoric acid (HF) as shown in the balanced chemical equation below:
XeF6 + 2H2O → XeOF4 + 4HF
Similarly, when xenon tetrafluoride (XeF4) reacts with water, it forms xenon trioxide hexafluoride (XeO3F6) and hydrofluoric acid as shown in the balanced chemical equation below:
XeF4 + 3H2O → XeO3F6 + 6HF
Xenon can also react with nitrogen to form xenon nitrate (Xe(NO3)2) when it is heated in the presence of nitric oxide (NO) as shown in the balanced chemical equation below:
Xe + 2NO + 2H2O → Xe(NO3)2 + 2H2
Moreover, xenon can react with chlorine to form xenon hexafluorochloride (XeClF6) when heated to high temperatures as shown in the balanced chemical equation below:
Xe + 3Cl2 + 6F2 → XeClF6 + 12F
Hydrolysis
Xenon tetrafluoride and hexafluoride are two compounds that can undergo hydrolysis reactions with water, leading to the formation of xenon oxide and hydrogen fluoride. The balanced chemical equation for the hydrolysis of xenon hexafluoride with water is:
XeF6 + 3H2O → XeO3 + 6HF
In this reaction, the xenon in XeF6 has a +6 oxidation state, which decreases to +4 in XeO3. Hydrogen fluoride is a byproduct of the reaction.
Formation of Xenates
Xenon trioxide, on the other hand, is a highly explosive white solid that is soluble in water. In strong alkaline solutions, it behaves as a weak acid, giving the xenate-6 anion. The balanced chemical equation for the reaction of XeO3 with hydroxide ions is:
XeO3 + 2OH– → XeO63- + H2O
In this reaction, XeO3 acts as a weak acid and donates a proton to the hydroxide ion, leading to the formation of the xenate-6 anion.
However, the xenate-6 anion is unstable in aqueous solutions and undergoes a disproportionation reaction to form xenon gas and xenate anions containing xenon in the +8 oxidation state (XeO64-):
3XeO63- → Xe + 2XeO64-
Xenon oxyfluorides can also be produced through controlled reactions of xenon hexafluoride with water or sodium nitrate. For example, XeF6 reacts with one equivalent of water to form XeOEF4 and two molecules of hydrogen fluoride.
The balanced chemical equation for this reaction is:
XeF6 + H2O → XeOEF4 + 2HF
Xenon oxyfluoride can also be formed by substitution of one or more fluorides in xenon fluoride or xenon tetrafluoride or by the reaction with strong oxy acids such as triplic acid or triplomethane sulfonic acid with the elimination of hydrogen fluoride.
Some Other Reactivities
Xenon and krypton compounds with bonds to elements other than fluorine are also known. For example, XeF2 can react with C6EF53 to form CEF5Xe and C6F5BF3-, which are alkyl species. These compounds have shapes similar to the fluorides.
Krypton and radon compounds are also known, but they are less reactive than xenon compounds. Krypton difluoride (KrF2) can be synthesized by reacting krypton with fluorine gas as shown in the balanced chemical equation below:
Kr + 2F2 → KrF2
Radon has been shown to form compounds with fluorine and oxygen, but they are highly unstable and decompose rapidly.
Group 18 compounds are unique due to their stable electronic configuration. The noble gases have a full valence shell, which makes them highly unreactive. However, under certain conditions, the noble gases can form compounds with other elements, such as fluorine and oxygen.
Share this:
| Element | Atomic Number | Symbol | Boiling Point (°C) | Density (g/L) | Electronegativity | Ionization Energy (kJ/mol) | Atomic Radius (pm) |
|---|---|---|---|---|---|---|---|
| Helium | 2 | He | -268.9 | 0.1786 | 4.160 | 2372.3 | 71 |
| Neon | 10 | Ne | -246.1 | 0.9002 | 4.787 | 2080.7 | 98 |
| Argon | 18 | Ar | -185.7 | 1.784 | 3.242 | 1520.6 | 120 |
| Krypton | 36 | Kr | -152.3 | 3.749 | 2.966 | 1350.8 | 128 |
| Xenon | 54 | Xe | -108.1 | 5.887 | 2.582 | 1170.4 | 131 |
| Radon | 86 | Rn | -61.8 | 9.73 | 2.60 | 1037 | 136 |
1 thought on “Noble Gases Chemistry of the Periodic Table”
Comments are closed.