What rule are hydrogen and helium excepted from?

Answer 1

The elements hydrogen and helium are exempted from the octet rule. The octet rule, as you might recall, states that elements prefer to have eight electrons in their valence shells. Hydrogen has a lone electron in its valence shell, and cannot begin to "borrow" electrons to create a shell with eight electrons in it. Remember that its electron, a 1s1 electron, is in the 1s shell. Helium has a full 1s shell with its two electrons (1s1, 1s2). It has no interest in any other electron configuration because its valence shell is full. The first two elements on the Periodic Table are the exceptions to the octet rule. A link can be found below.

Answer 2

Hydrogen and helium are exceptions to the octet rule in chemical bonding. Hydrogen can either gain one electron to achieve a duet configuration or lose one electron to be left with a single electron. Helium is already stable with two electrons in its outer shell.