Helium is an inert gas.Its atomic number is 2 as we know 1st orbital of element occupy maximum 2 electrons so these 2 electrons are filled up in 1st electronic orbital.Hence,Helium has zero valency.
Atomic number of Calcium 20. Maximum 2 electrons can come in 1st orbit and then all orbits have 8 electrons in them. So the electronic configuration of Ca will be 2,8,8,2.
As last orbital has 2 electrons and maximum capacity is of 8 electrons so these 2 electrons are valence electrons and Calcium has a valency of 2.

I hope it is now clear to you.Thanku

Valency of Helium

Helium is a noble gas and is placed in Group 18 of the periodic table. It has an atomic number of 2 and its electronic configuration is 1s². The valency of an element is determined by the number of valence electrons it has. Valence electrons are the electrons present in the outermost shell of an atom.

Valency of Helium

Helium has a completely filled outermost shell with 2 electrons. This makes it highly stable and unreactive. Since it already has a filled shell, it does not readily gain or lose electrons to form compounds. As a result, helium has a valency of 0.

Valency of Calcium

Calcium is an alkaline earth metal and is placed in Group 2 of the periodic table. It has an atomic number of 20 and its electronic configuration is 2, 8, 8, 2. The valency of calcium is determined by the number of valence electrons it has.

Valency of Calcium

Calcium has 2 valence electrons in its outermost shell. In order to achieve a stable configuration, calcium loses these 2 electrons to form a cation with a +2 charge. By losing these electrons, calcium achieves a noble gas configuration similar to argon. Therefore, the valency of calcium is +2.

Relationship between Helium and Calcium Valency

Helium and calcium have different valencies due to their different positions in the periodic table. Helium, being a noble gas, has a completely filled outermost shell and does not readily react with other elements. Therefore, its valency is 0.

On the other hand, calcium, being an alkaline earth metal, has 2 valence electrons in its outermost shell. It tends to lose these electrons to achieve a stable configuration, resulting in a valency of +2.

In summary, the valency of helium is 0, while the valency of calcium is +2. This difference in valency is due to the distinct electronic configurations and positions of these elements in the periodic table.