Oktette Roman – Wikipedia
The Octet rule or Eight-electron rule is a classic rule of chemistry. It states that the electron configuration of atoms of the main group elements from the second period of the periodic system in molecules in molecules is a maximum of eight external electrons (valence electrons) or four pairs. So the atoms strive to accept the noble gas configuration. The octet control is a special case of the more comprehensive noble gas rule. [first]
Atoms that usually behave according to the octet rule [ Edit | Edit the source text ]
The octet bar often only applies to the main group elements of the 2nd period. This includes the elements carbon, nitrogen, oxygen and fluorine. In most of their compounds, these elements reach the electron configuration of the noble gas neon. The carbon, nitrogen and fluoron atoms also have in their elementary state- as a diamond or fullere 2 ), Trisauerstoff- (O 3 , Ozone) and difluormolecule (f 2 )-The neon electron configuration with eight valence electrons. For all atoms mentioned, it applies that they can be surrounded by less than 8 electrons (e.g. as R 3 C + , Carbocation), but never of more than 8.
The octetta rule applies to most stable connections of the above -mentioned elements. But there are exceptions. There are significantly more exceptions for elements of the higher periods. Elements such as tin and lead also form cations in the two -value oxidation level with a lonely electron pair (relativistic effect).
However, there are many molecules in which only the electron octet is formally exceeded (octetta extension). Typical examples of this are phosphorenta fluoride (PF 5 ), Sulfurhexafluoride (SF 6 ) or iodheptafluoride (if 7 ). In the past, unoccupied unoccupied d-orbitals were often energetically sought for the binding electrons that go beyond the octet. However, more detailed quantum mechanical considerations show that D orbitals should not play an important role due to the enormous difference in energy to the S- and P valence orbitals. Alternative descriptions of these molecules use multi -center bonds or partially ionic formulations (e.g. Pf 4 + F – , SF 4 2+ (F – ) 2 , IF 4 3+ (F – ) 3 ).
Molecules, for which octet-level-compliant Lewis formulas can be set up, but in which formulas with more than 4 binding lines are often used should not be seen as exceptions. Sulfuric acid or sulfur dioxide are mentioned here as typical examples.
Hydrogen and the light cations Li + , Be 2+ and B 3+ Do not fulfill the octet control because they have too few electrons and the associated noble gas configuration (helium), which is reached in connections, only has two electrons. However, this is more of a formal classification, but they meet the noble gas rule.
Nitrogen and oxygen [ Edit | Edit the source text ]
Exceptions are, for example, the nitrogen oxide nitrogen monoxide NO, also called nitrogen oxide, and the nitrogen dioxide NO 2 . The molecules of these compounds are constant radicals, so they have an odd number of electrons, which is basically incompatible with the octet rule. [2]
Another exception to the octet bar is the disuse material molecule o 2 : Measurements show that it contains two unpaired electrons. The noble gas configuration requires paired electrons. Disauer fabric molecule can be in the reaction of potassium, rubidium and caesium with air into the hyperoxide ion o 2 – pass; The hyperoxides are created 2 , RBO 2 and cso 2 .
The hyperoxide ion has an odd number of electrons and therefore also no octet.
No validity for unstable intermediate stages [ Edit | Edit the source text ]
The rule applies above all to insulated compounds. In many reactions, unstable but demonstrable intermediate products occur, which the octet rule does not obey, e.g. B. radicals such as chlorradical or carbocations in which the carbon only has six electrons, for example in the implementation of butyl chloride. Nitrene and carbene are also mentioned.
In the case of transition metal compounds, you will find an analogous rule: the 18-electron rule. However, this is – if at all – only well fulfilled for complexes with predominantly covalently bound ligands, but even here there are countless exceptions.
- ↑ Entry to Lewis octet rule. In: iupac (ed.): Compendium of Chemical Terminology. The “Gold Book”. doi: 10.1351/goldbook.LT07065 – Version: 2.1.5.
- ↑ Charles E. Mortimer, Ulrich Müller, Johannes Beck: Chemistry: The basic knowledge of chemistry. Stuttgart 2015, ISBN 978-3-13-484312-5, S. 128.
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