Why do atoms follow octet rule?

  1. when forming bond why do some atoms follow and some atoms [cations(d block )] don't follow octet rule and why does the formal charge should be lowered?
  2. jcsd
  3. PhysicoRaj

    PhysicoRaj 430
    Gold Member

    Because atoms form bonds in order to get stable, i.e., attain the nearest noble gas configuration (noble gases have eight electrons in the outer shell), rather than just blindly fill their orbitals with eight electrons. They might do this by either gaining, losing or sharing electrons. The octet rule holds good only for elements with atomic number <20 because they attain noble gas configuration by doing so while transition metals won't (noble gases are p-block, ns2 np6). d and f block elements have vacant d orbitals, while hydrogen and helium do not have any 1p subshell. I've heard of some dodectet and 18-electron rule which are used to explain the bond forming of transition metals.
    Lower FC indicates a better electronic distribution, which in turn increases the stability.
  4. why does noble gas configuration stable than other configurations?
  5. DrDu

    DrDu 4,639
    Science Advisor

    Electrons have lower energy in bonds than in single atoms. So an atom will try to form as many bonds as possible.
    This is counteracted by the Pauli principle, stating that electrons want to stay away from each other. Hence atoms will only form bonds if the bonds are sufficiently strong to overcome Pauli repulsion.
    In the first row atoms, s and p orbitals are of approximately of the same size and energy, so that all get equally involved in bonding (thus usually 4). In higher rows, the octet rule will usually not apply as neither are s and p orbitals of same size (giving rise to different bond strength) and d orbitals (at least in main group elements) being to high in energy to participate. Furthermore, much of the bonding will be of ionic type.
    In summary: The octet rule is a relic of the afterlast century and is of little relevance today in most part of chemistry.
    1 person likes this.
  6. so atoms can be stable
  7. Because they contain a full valence shell of electrons.
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