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Helium Facts: The ElementHelium Facts: Structure, Properties and Isotopes The element Helium is the second lightest element in the universe, yet it is over four times as massive as Hydrogen. This is due to the presence of not just two protons in its nucleus (and hence the Atomic Number of 2) but also two neutrons. This means it has 4 nuclear particles and so it is called 4-Helium. The element can be represented like this:
Other Isotopes of Helium 
The increased number of protons and neutrons when compared to Hydrogen gives Helium many more possibilities for isotopes where the number of neutrons differs from two. Clearly, the options are one proton (a total of 2 protons + 1 neutron = 3 nuclear particles), or three neutrons or more.
Of all the possibilities, only Helium with one proton instead of two (called 3-Helium) is stable. It is quite rare, making up only 0.0001% of any given sample of Helium.3-Helium alone is the only stable isotope of this element. There are many others, all with successively larger numbers of neutrons in the nucleus. These are 5-Helium, 6-Helium, 7-Helium, 8-Helium and 9-Helium. How they compare to 4-Helium is presented below:
The instability of the larger Helium nuclei in these isotopes is not linear, and so 6-Helium has a longer half-life than 5-Helium. Chemical Bonding of Helium Helium has electrons only in its first shell. There is only room for two electrons in that shell, which is comprised of a singe s-subshell. Since neutral atoms of Helium already have two electrons and therefore a full outer shell, Helium does not react with other elements. It is what is called a Noble Gas; individual atoms that do not bond with other elements under any normal circumstances. Therefore Helium gas is made from single Helium atoms. |
