the octet rule is not a rule that was made by usin any calculation it was made by a guy named G.n lewis . it just agreed to the periodic table made by mendeleef because by his observation this sort of octets kept repeating in the elements of the table . yes there are exceptions to this rule i.e the duplet rule used in Helium , & the 18 electron rule which overrides this rule in D & F row elements electrons
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