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Posted: Tue May 08, 2018 10:31 am
Why are H, He, Li, and Be exceptions to the octet rule?
Posted: Tue May 08, 2018 3:47 pm
These are exceptions to the octet rule, because these elements have too few valence electrons to form an octet. The orbitals that these elements can fulfill (which are only in the s-state) do not allow for an octet. For example, the p-state has 3 orbitals, which has a maximum of 6 electrons, and the p-state cannot be reached until you are looking for the electron configuration of the element of boron and beyond. The s-state and the p-state combined allow for 8 valence electrons. I hope this helps!!
Posted: Tue May 08, 2018 3:54 pm
A more general rule (or guideline) is that elements will gain or lose electrons until the outermost shell is full. For elements in the second row such as C, N, O, and F, this means they gain electrons until the n = 2 shell is full. The n = 2 shell can hold 8 electrons, so in this case the rule is the same as the octet rule. For H, He, Li, and Be, they will gain or lose electrons until the n = 1 shell is full, therefore they will only have 2 valence electrons.
Posted: Sun May 13, 2018 12:25 pm
because they have less than 8 electrons so they don't fill valence s and p orbitals