What kind of element is neon
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The noble gases include the elements of group 18 and main group VIII:
- Xenon and
All elements are atomic. They are all colorless, non-toxic, non-flammable gases. In the solid state, with the exception of helium, they crystallize in the cubic closest packing of spheres.
The group name
The outstanding characteristic of the noble gases is their chemical inertness. This is where the name noble gas comes from in analogy to noble metals, which are also inert.
The noble gases have the electron configurations2p6 or. s2 for helium, the completely filled noble gas shell which all atoms strive for. The closed valence shell without unpaired electrons is responsible for the fact that the noble gases are very inactive.
The noble gases were considered inert for many years, as no compounds were known and, according to the octet theory, are not possible either: the noble gases have no unpaired electrons. The fact that there are some noble gas compounds is due to the decreasing ionization and promotin energy for states with unpaired electrons in the heavier noble gases.
In 1962, Rudolf Hoppe and four American chemists discovered noble gas fluorides at the same time. Later it was also possible to synthesize compounds of xenon with oxygen, nitrogen and carbon. However, only the xenon fluorides are thermodynamically stable.
In each period the noble gas has the highest ionization energy, a sign of the particularly stable electron configuration. Since the electrons of the outermost shell are less strongly bound with increasing atomic number, the ionization energy within the group decreases from helium to radon.
The low melting and boiling points reflect the weak forces of attraction between the atoms, these are only caused by van der Waals forces. The increasing size of the electron cloud explains the increase in van der Waals forces due to easier polarizability and thus the increase in melting and boiling points from helium to radon. Helium has the lowest melting point of all known substances.
Occurrence and extraction
Noble gases can be found in the air, in natural gases and in minerals. The volume fraction of noble gases in the air is 0.935%, with argon having the largest noble gas fraction of 99.8%.
- Tab. 1
- Fraction of noble gases in the air
|Volume fraction [%]|
Helium is mainly obtained from natural gas. Due to the high proportion of helium, extraction from these natural gas storage facilities is significantly more economical than from air liquefaction. The other noble gases - neon, argon, krypton and xenon - are obtained exclusively from air.
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