Why is helium listed in group 18

This reflects the stability of their electron configuration and points again to their relative lack of chemical reactivity. In recent years, however, this term has fallen out of favor, although you will occasionally see it in older literature. Scientists have discovered that, since the heavier noble gas atoms are held together less strongly by electromagnetic forces than are the lighter noble gases, such as helium, the outer electrons of these heavier atoms can be removed more easily.

Because of this, many compounds of the gases xenon, krypton, and radon can, in fact, be formed. Of the six noble gases, only krypton, xenon, and radon have the ability to form stable compounds. These are used as oxidizing agents. The noble gases glow in distinctive colors when used inside gas-discharge lamps, such as neon lights.

Xenon is commonly used in xenon arc lamps, which are present in film projectors and automobile headlights due to their nearly continuous spectrum that resembles daylight.

The noble gases are also used in excimer lasers, which are based on short-lived electronically excited molecules known as excimers. Argon can also fill fluorescent and incandescent light bulbs, creating the blue light found in "neon lamps.

This insulation barrier improves the windows' energy efficiencies. Argon also creates an inert gas shield during welding, flushes out melted metals to eliminate porosity in casting, and provides an oxygen- and nitrogen-free environment for annealing and rolling metals and alloys. Similarly to argon, krypton can be found in energy efficient windows. Because of its superior thermal efficiency, krypton is sometimes chosen over argon for insulation. Krypton is also found in fuel sources, lasers and headlights.

In lasers, krypton functions as a control for a desired optic wavelength. It is usually mixed with a halogen most likely fluorine to produce excimer lasers. Halogen sealed beam headlights containing krypton produce up to double the light output of standard headlights. In addition, Krypton is used for high performance light bulbs, which have higher color temperatures and efficiency because the krypton reduces the rate of evaporation of the filament.

Xenon has various applications in incandescent lighting, x-ray development, plasma display panels PDPs , and more. Incandescent lighting uses xenon because less energy can be used to obtain the same light output as a normal incandescent lamp. Xenon has also made it possible to obtain better x-rays with reduced amounts of radiation.

When mixed with oxygen, it can enhance the contrast in CT imaging. These applications have had great impact on the health care industries.

Plasma display panels PDPs using xenon as one of the fill gases may one day replace the large picture tubes in television and computer screens. Nuclear fission products may include several radioactive isotopes of xenon, which absorb neutrons in nuclear reactor cores. The formation and elimination of radioactive xenon decay products are factors in nuclear reactor control.

Radon is reported as the second most frequent cause of lung cancer, after cigarette smoking. However, it also has beneficial applications in radiotherapy, arthritis treatment, and bathing. In radiotherapy, radon has been used in implantable seeds, made of glass or gold, primarily used to treat cancers.

It has been said that exposure to radon mitigates auto-immune diseases such as arthritis. Some arthritis sufferers have sought limited exposure to radioactive mine water and radon to relieve their pain. The History The first person to discover the noble gases was Henry Cavendish in the late th century.

Let us begin the discussion of the trends in the first ionization potential. Placement of H over Li and He over Be leads to the following picture: the normalized I P drops considerably between H and Li and between He and Be emphasizing the well-known substantial discrepancy between the properties of elements from Period 1 and Period 2 , and then drops more smoothly for the subsequent periods only Period 7 elements slightly bend this trend as compared to their Period 6 counterparts due to well-known relativistic effects.

Similar trends is seen for Groups 17 and 18, albeit the fall of normalized I P is not as dramatic recall, we now start with Period 2 elements, F and Ne, as the first members of their series. Remarkably, Group 1 and Group 2 elements show quantitatively very similar behaviour, so do Group 17 and Group 18 elements. This emphasizes the fact that for the former it is the s shell which is ionized, while for the latter it is the p shell.

Precisely this argument has been used by Bent Bent who was fierce advocate of situation C in Fig. If, however, we accept that H should be placed together with halogens while helium should join other noble gases, the picture of normalized I P changes substantially. Although the normalized I P values fall as before with the increase of the Period number, yet there appear marked quantitative differences between the first two groups of elements Groups 1 and 2 , as well as between the latter two Groups 17 and Finally, if we decide to follow the traditional placement with H in Group 1 and He in Group 18, the discrepancies between the trends seen for Group and Group 2 are even larger than in the previously discussed case.

The supplemental analysis of the normalized E A concerns two major situations: H is placed in Group or in Group The placement of He does not matter here since its E A is null, and therefore it fits either Group 2 with Be showing the same value or Group 18 Ne having the same feature.

Among the two situations the one with H placed in Group 1 seems more natural, as the normalized E A value drops slowly for Group 1 elements again, except the reversed trend from Period 6 to Period 7 due to relativistic effects. However, if H is placed in Group 17, as advocated by some, the normalized E A skyrockets up to nearly 5, since the values for F and Cl are much larger than that for H.

Thus, the traditional placement of H in Group 1 does indeed have more pros than cons, and more supporters. Taking this altogether, it seems that placement of H over Li and He over Be leads to the most balanced picture, with natural trends for both the normalized I P and the normalized E A as one goes down the four respective Groups of the Periodic Chart. So, what do we have to lose by placing He over Be? Some Pros and Cons are displayed in Table 1. As it may be seen in Table 1 , there are a few Pros as well as some Cons against the placement of He in Group 2.

Simultaneously, in the traditional constructions of the periodic Chart Fig. However, among numerous Pros for placing He above Be, one notices that such placement reproduces consistently the large gap between properties of Period 1 and 2 elements. In other words, nonmetals open Groups 1 and 2 where mostly metals reside.

Hydrogen is as much an alkali metal as helium is an alkali earth metal as Fig. As Schwarz has insightfully put it in his e-mail exchange with this author , there are as many versions of the Table as many features you expected to be assembled, rationalized, and taught to students.

This is definitely true. There is no single way to solve this puzzle. So I am following personal idiosyncrasies here. Footnote 2 What an experimentalist in me expects from the Periodic Table when I teach students, is that—aside from its key feature, periodicity—I may easily follow the trends of element properties as I go down the Group.

And that they will make qualitative and semi-quantitative sense while relativistic effects may be blamed for small deviations seen for the heaviest elements. And as a computational chemist, I value clear separation of elements with s, and p shells being systematically occupied by electrons.

Thus, to my personal taste, Periodic chart should look like in Fig. My impression was that you like the so-called left-step or Janet form of the Periodic Table PT , which fulfills one of the three requirements on PTs 1. A drawback of this form is that the physical origin and background of the chemical trends is less well reproduced. Of course, the final decision on the preferred form of the PT depends on the relative weights, one puts on the criteria of beauty and chemistry.

The presented manuscript received valuable comments during the peer-review process. They represent interesting and critical point of view.

Some of them are given below, together with the responses from the author. R:: There is some feeling of unreality about the debate where to put He, both in this paper and in general discussions in the literature. The viability of the Periodic Table lies in its being an organizational paper tool for similarities that accepts differences.

However, the major effort beyond creation of the Table was driven by quest for similarities and not for differences. Only after the similarities helped to build the Table, one could dwell into differences. This author claims simply that more essential similarities are better revealed by placement of He in Group 2.

But there are certain, rare but important, properties, such as the very notion of inertness, which are better reflected by traditional placement of He. Difference is accepted as one goes down the Table, why not accept it as one goes up, as is the case with He? This is important argument. However, the departure from trends in chemical properties for heavy elements as one goes down the Group are well understood based on the impact of relativistic effects.

However, important trends do not change for the lightest Group members, hence if we start accepting that for He, we may rebuild the entire Periodic Table to accept even more. Personally, I dislike such post-modernistic possibility. I do not like the identification in italics of "chemical compounds" with neutral molecules.

Charged molecules or bonded ions from carbonate to borohydride have a right to be called compounds. Perhaps some effort in fact might be directed to making salts of the stable noble gas ion molecular units. The referee is right about the effort of making salts of the stable noble gas ion molecular units — this was discussed extensively by Christe and it is cited here.

But this does not change the attitude of most chemists towards ions — since you cannot isolate 1 mol of them in the bottle, they are not compounds. They are molecules, but not compounds. Yet this is neutral HArF which is considered by the community to be the first isolable compound of Ar. Otherwise, no one would pay attention to this discovery. I agree with those who restrictively claim that only neutral species may be called compounds. And also with those who agree that ions have chemistry obviously!

But there is no contradiction between these two claims! There might be some chemistry of He anion, which is not bound in its ground state, but one excited state has a reasonable lifetime.

I agree but I would not like to dwell into excited states. Excited states always have rich chemistry, so if one examines neutral He atom with its unreactive doublet and excites it to the 1s12s1 configuration, it may even form a doubly bonded He2 molecule! Indeed, the diagram of electronic states of He2 reveals many bonded excited states. Excited He and Ne are not inert at all. While the Table reveals mostly the ground state properties.

Antoniotti, P. A 16 , — Article Google Scholar. A 40 , — Bartlett, N. Google Scholar. Nature , — Belpassi, L. Bent, H.

AuthorHouse, Bloomington See how this Interactive Periodic Table helps you. Visit Periodic table. Helium element is in period 1 and group 18 of the Periodic table. Helium is the p-block element and it belongs to the Noble gases group. Helium is the element which has 2 electrons only, and these two electrons are nothing but they are the valence electrons. Note: Generally for all the elements, octet is the stable configuration. But helium is the only exception in which duplet configuration is stable.

Helium shows the very similar physical and chemical properties as that of the group 18 elements. Helium element do not react with other elements and hence it is chemically inert.