Noble gases got their name because it was long thought that the elements of VIII. Main group would not react with other elements or substances due to their fully occupied outer electron shells. Today they are used, among other things, as shielding gases because the inert gases are non-flammable and non-toxic. Even in everyday life one encounters the noble gases from time to time.
In the meantime, it has been possible to make noble gases react with other reactive substances under particularly extreme conditions, so that a few noble gas compounds are known.
Halogens and noble gases
#periodic system #elements #main groups #halogens
Structure of the electron shell
The noble gases make up the VIII. Main group in the periodic table of the elements. They have a completely filled outer electron shell with 2 (He), 8 (Ne, Ar) or 18 (Kr, Xe) outer electrons, which represents an extraordinarily stable state.
Noble gases can therefore only with difficulty take up an electron or give up an electron to a reaction partner. That’s why noble gases have the highest ionization energies of all elements, meaning an enormous amount of energy must be expended to separate even one electron from the outer shell. However, accepting or emitting an electron would be a prerequisite for the formation of a chemical bond. Since they generally do not react with other substances, they got their "elegant" name: "the noble gases" – noble gases. If an electron shell is fully occupied, one therefore also speaks of a stable electron shell " Noble gas state " respectively. the "noble gas configuration.
Since the elements of VIII. Since they already have a fully occupied valence shell in the main group, they do not form molecules and occur as monatomic gases under normal conditions. All other elements strive to reach the noble gas state and therefore enter into compounds (NaCl) or form molecules (oxygen, nitrogen).
Properties of the noble gases
The elements helium belong to the noble gases , Neon , Argon , Krypton , xenon and radon . Due to the fully occupied outer electron shell, the elements are chemically very inert ("inert"). They are gaseous at room temperature because they all have very low boiling points. Of all the elements, helium has the lowest boiling point of all; it is only boiled at ca. 4 K liquid, which corresponds to -269 °C.
Noble gases are neither flammable nor combustible and they do not react with any chemical element or compound under normal conditions. With the exception of radon, which is a radioactive element, the noble gases are harmless to humans. They are colorless and odorless gases.
Only under special conditions can the noble gases xenon, krypton, and radon form compounds with reactive elements, such as fluorine, chlorine, or oxygen. In 1962, by reacting xenon with platinum hexafluoride, the compound Xe+PtF6 – the first noble gas compound – was produced. A short time later the preparation of the xenon fluorides XeF2 and XeF4 succeeded.
Will z. B. Xenon mixed with fluorine gas and this mixture irradiated with high-energy light produces 2 fluorine atoms from F. These atoms are so aggressive that they even snatch an electron from the xenon atom. Thus, different xenon fluorides can be prepared one after the other.
F 2 → 2 F X e + 2 F → X e F 2 X e F 2 + 2 F → X e F 4 X e F 4 + 2 F → X e F 6
Today, other compounds , such as XeO2F2, XeO4, Ba2XeO6, CsXeF7, XeCl2, but also compounds with xenon-nitrogen bonds or xenon-carbon bonds known. Also from other noble gases there are compounds like KrF2 or RnF2 and more and more are discovered. All xenon compounds are strong oxidizers. Many compounds are relatively unstable and decompose again quickly. Others can be isolated. Until now it has not been possible to perform reactions with the noble gases helium and neon.
Noble gases occur in the atmosphere of our earth in small amounts. They are obtained by fractional distillation of liquid air. Nitrogen and oxygen can also be chemically removed by passing air over heated magnesium.
2 Mg + O2 -→ 2 MgO
3 Mg + N2 -→ Mg3N2
|Average composition of dry air in the troposphere (volume fractions in percent)||ϑ V in °C|
|Carbon dioxide||0,040||-78.4 (sublimated)|
Already CAVENDISH stated that apart from the gases oxygen, nitrogen and carbon dioxide other substances had to be present in the air.
Helium is not only present in air, but also in natural gases. Some of the helium on Earth is produced by the decay of radioactive elements and is trapped in rock formations.