Concept of Exceptions

[Matia Kim 1B]

Why is it that elements in the third row and below have octect exceptions instead of elements earlier in the periodic table?

[salvadoralvizo1J]

Elements on the third row on the p-orbital have higher energy than 3-D electrons. Since third row electrons don't have any electrons on the 3D orbital, valence electrons can fill in the empty row.

[KateCaldwell 1A]

I believe it would be due to the larger radii in the first two rows as the electrons cannot interact with the nucleus. Exceptions usually occur when molecules have an odd number of electrons, molecules that contain atoms that have less than an octet, and molecules that contain atoms with more than an octet.

[Gabi Landes 1-H]

Third period elements occasionally exceed the octet rule by using their empty d orbitals to accommodate additional electrons
Size is also an important consideration:
The larger the central atom, the larger the number of electrons which can surround it
Expanded valence shells occur most often when the central atom is bonded to small electronegative atoms, such as F, Cl and O

see:http://www.mikeblaber.org/oldwine/chm1045/notes/Bonding/Except/Bond08.htm

[ErinKim1I]

I think about it this way:
s-orbitals can hold 2 e-
p-orbitals can hold 6 e-

so s and p together can hold 8e-, which is an octet.
But starting from row 3 of the periodic table, there is a d-orbital, and d-orbitals can hold up to 10e-.

So if an element has s, p, and d orbitals, the electrons in the d-orbitals can add to the 8e- from s & p, which exceeds an octet.