Group 18: Noble Gases Family

Generally, group 18 elements are considered as inert gases. So-called “inert” substances are so named since these cannot not combine using any other substances. Alternative names for the noble gases. They don’t contribute anything to the experience other than being odorless and tasteless. They exist with in environment in minute concentrations. In fact, they make up only one percent of the total atmosphere. They are also found in some compounds. The only elements that are not yet prepared from compounds are helium and neon. The group contains elements such as Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn) and Oganesson (Og). These elements are monoatomic and have a stable octet or duplet electron arrangement. They also have full outer shells, which makes them very stable. Oganesson is a synthetically produced radioactive element. It has a half-life of 3.8 days. Noble gases are located at the extreme right hand side of the long periodic table. The Van Der Waals force between noble gases is relatively weak, which allows the molecules to liquefy without much energy being used (Peterson, 2003).

 

1. Electronic configuration of Group 18 elements

Group 18 elements have a stable electronic configuration and a high positive electron gain enthalpy. They have a full outermost valence shell. It consists of 8 electrons. General electronic configuration of group 18 is ns2 np6. While the electronic configuration of group 18 members is as follows (Chen & Hill, 2011).

 

He [2] 1s2
Ne [10] 1s2 2s2 2p6 or [He] 2s2 2p6
Ar [18] 1s2 2s2 2p6 3s2 3p6 or [Ne] 3s2 3p6
Kr [36] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 or [Ar] 3d10 4s2 4p6
Xe [54] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 or [Kr] 4d10 5s2 5p6
Rn [86] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 or [Xe] 4f14 5d10 6s2 6p6
Og [118] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6 or [Rn] 5f14 6d10 7p6

 

2. Trend in the physical properties of Group 18 elements

These gases have extremely low density, and are poor conductors of heat. In particular, their melted and boils temperatures are rather low. They have high ionisation energies and are sparingly soluble in water. The electron gain enthalpy is more negative for halogens than for noble gases. More electrons are added to an orbit that is greater in energy. They can also fill unoccupied orbitals in heavier noble gasses. But they can never be added to the outermost shell of halogens (Wolchok, et al., 2013).

 

2.1. Atomic radius of Group 18 elements

Group 18 elements have no ionic radii because these elements do not form ions. Atomic radii of group 18 elements increases from helium to radon as the number of atoms increases, .while atomic radii of Oganesson is unknown .Similarly atomic radius of argon is smaller than Neon.

 

Atomic radius group 13 periodic table />

 

Figure 1: Atomic radius of Group 18 elements

 

2.2. Ionization energy of Group 18 elements

Ionization energy of group 18 elements decreases from top to bottom.

 

First ionization energy group 13 periodic table />

 

Figure 3: First Ionization Energy of the Group 18 elements

 

2.3. Electron gain enthalpy of Group 18 elements

Electron gain enthalpy of noble gases is the energy released when a gaseous atom accepts an extra electron. It is measured in electron volts per atom. The electron gain enthalpy of noble gases increases with increasing atomic size. It is less negative for elements with full orbitals. It becomes more negative when a group is moved from left to right. The nuclear charge of an element also increases with increasing atomic size.

 

2.4. Melting and boiling point of Group 18 elements

Boiling point and melting point increase along with the atomic size from helium to radon while melting and boiling point of Oganesson is unknown.

 

melting and boiling points group 13 periodic table />

 

Figure 4: Melting and Boiling Points of the Group 18 elements

 

3. Chemical nature of group 18 elements

• The reactivity of the noble gases depends on the behavior of the outermost electrons. They do not gain electrons. Unlike other elements, group 18 elements do not react with other elements and do not enter into typical chemical reactions. The octet or duplet electron arrangement of noble gases ensures that they are unreactive.
• The chemical nature of group 18 elements is characterized by high ionization enthalpies, high ionization potentials, and very stable electronic configurations. These properties lead to higher vaporization enthalpies, and increased solubility Group 18 elements also display large positive values of electron gain enthalpies. The octet electron arrangement and the duplet electron arrangement are both stable electron arrangements within the outermost shell.
• The valence electrons are considered a defining characteristic of the chemical properties of group 18 elements. The behavior of the outermost electrons is a key factor in determining the reactivity of an element. In noble gases, these electrons reach the p-subshell. It is possible to synthesize compounds of these elements under extremely low temperatures.

 

4. Uses of group 18 elements

Noble gases have following important uses (Chen & Hill, 2011).
• These gases are used in blimps, balloons, incandescent light bulbs, as a component of breathing gases, in metallurgical processes and in NMR spectroscopy. These gases are not commonly used in chemical reactions, but they do have very stable electronic configurations. They can be used to make compounds with other elements, such as Krypton fluorides, but only under extreme conditions. They are also used in light bulbs for special purposes.
• They can be used to produce lasers, or to image the heart and brain. These primarily serve as sterile altitudes in elevated metallurgy operations, and as discharging conduits as advertising. Hormonal changes which help make red blood cells are also made using these.

 

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Conclusion

Located in the far right of the periodic table, group 18 elements are also known as noble gases. Besides Xenon, they include Argon, Radon, and Krypton. They are odorless, tasteless, and colourless. They are almost inert, but can be condensed at low temperatures. Despite their low abundance on earth, group 18 elements are found in some compounds. These compounds are not known to Mendeleev. However, they are known to be useful in high temperature metallurgical processes.

 

References

1. Peterson, K. A., Figgen, D., Goll, E., Stoll, H., & Dolg, M. (2003). Systematically convergent basis sets with relativistic pseudopotentials. II. Small-core pseudopotentials and correlation consistent basis sets for the post-d group 16–18 elements. The Journal of chemical physics, 119(21), 11113-11123.
2. Chen, I. C., Hill, J. K., Ohlemüller, R., Roy, D. B., & Thomas, C. D. (2011). Rapid range shifts of species associated with high levels of climate warming. Science, 333(6045), 1024-1026.
3. Wolchok, J. D., Kluger, H., Callahan, M. K., Postow, M. A., Rizvi, N. A., Lesokhin, A. M., … & Sznol, M. (2013). Nivolumab plus ipilimumab in advanced melanoma. N Engl J Med, 369, 122-133.