Chemistry - To which block of the periodic table does helium belong?

Solution 1:

Blocks in the periodic table should not be mixed up with groups (like noble gases). The reason why Helium is considered a noble gas is because its outermost (and at the same time only) shell is fully occupied by its 2 electrons. When you look at the electron configurations in the PTE you can see that the first element which happens to have an occupied p-orbital is boron. Due to this fact boron also has to be the first p-block element, since the block definition is as follows:

An element belongs to the block x, if the electron, which is added in comparison to the previous element (by atomic number), is in an orbital of type x in the ground-state electron configuration of that element.

Or the fast explanation: Why should helium be considered a p-block element, if it doesn't even have any electron in a p-orbital or any shell including a p-orbital?

Solution 2:

Helium is an s-block element with properties like those of the p-block noble gases.

In a periodic table more concerned with chemical behaviour you're likely to see He in the p-block.

In a table more concerned with showing the filling of electron shells you're likely to see He in the s-block.

The optimal solution is to show He in the s-block but to colour it as a noble gas or a p-block element.