Question

Helium has two valence electrons, and these electrons sre located in the 1s subshell. Without using the periodic table, in which group and period is helium located?
A .Group 8A, Period 1

B. Group 6A, Period 3

C. Group 3A, Period 3

D. Group 3B, Period 6

Answer 1

Answer: Option (A) is the correct answer.

Explanation:

Atomic number of helium is 2 and its electronic configuration is $1s^{2}$. As here n = 1 this means that helium element belongs to period 1.

Since, helium atom has completely filled s-shell this means that it is unreactive in nature as it neither needs to lose or gain an electron in order to attain stability.

And, all the unreactive elements in the periodic table belongs to group 8A. That is why, helium also belongs to group 8A and period 1.

Thus, we can conclude that helium is located in Group 8A, Period 1 .

Answer 2

The answer iiiis... A: Group 8A, Period 1

Here's why:

The way I found this doesn't have much thought or explanation--I just remember that helium and hydrogen are in period 1. The only answer choice with "period 1" is A.