Question

How many valence electrons does a helium atom have? what is the formula of the ion formed when potassium achieves noble-gas electron configuration?

Answer 1

> How many valence electrons does a helium atom have?

The electron configuration of Helium is simply 1s2. We see that its outermost shell is the s shell and it contains 2 electrons, therefore the number of valence electrons is also 2.

 

> What is the formula of the ion formed when potassium achieves noble-gas electron configuration?

Potassium has a electron configuration of [Ar] 4s1. To have an electron configuration of only [Ar] which is a noble gas, the one electron from 4s1 should be removed, hence:

K+