Name: Lewis Dot Structures
Uploaded: 2019-07-19
Duration: 4 min 41 s
Description: Lewis dot structures, also called electron-dot structures, describe the chemical bonding between atoms in a molecule. Watch the video to learn more.

Question

Define octet rule. Write its significance and limitations.

Accepted Answer

The octet rule (electronic theory) of chemical bonding was developed by Kossel and Lewis. According to this rule, atoms can combine either by transfer or share of valence electrons from one atom to another to attain the nearest noble gas configuration by having an octet in their valence shell.
Or

The following are the limitations of the octet rule:
(a) The rule failed to explain the shape and relative stability of molecules.
(b) It is based upon the inert nature of noble gases. However, some noble gases like xenon and krypton form compounds such as $X e F_{2}, X e F_{4}, X e F_{6}, X e O_{2} F_{2}, K r F_{2}$ , etc.

(c) Expanded Octet: The octet rule cannot explain the stability of compounds which have more than eight valence electrons around the central atom i.e octet is expanded. For example, $P F_{5}, S F_{6}$ , $X e F_{4}, X e F_{6}, X e O_{2} F_{2}, I F_{7}$ , etc.

(d) Stability of odd electron species: The octet rule is not satisfied for atoms in a molecule having an odd number of electrons. For example, $N O$ and $N O_{2}$ do not satisfy the octet rule.

Here, the octet of nitrogen is not complete.

(e) Electron-deficient compounds: This rule cannot explain the existence of compounds in which the number of electrons surrounding the central atom is less than eight. For example, $L i C l, B e H_{2}, B F_{3}, A l C l_{3}$ , etc. do not obey the octet rule.

Define octet rule. Write its significance and limitations.

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