Even though e-configuration of Helium is 1s2 ,instead of 2nd group its placed in 18th group why?

Question

chemistry

Answer 1

according to the octet rule, the electron configuration needed by He atom is 1s2. It means He atoms has complete octet needed as it contains 2 electrons only. also it is unreactive toward other elements w/c make it a noble gas (group 18)

Answer 2

There are some periodic tables that place He above Be which also has 2 electrons in the s-orbital.

http://www.ipgp.jussieu.fr/~tarantola/Fi...

But then we lose track of the most important characteristic of helium.  That it is an inert gas, and so for that reason, it is lumped in with the rest of the inert gases.

Or we could argue that a completely filled lone s-sublevel makes for a stable arrangement, just like a filled p-sublevel.

The first row of the PT contains the "oddballs".  We could also ask, why include hydrogen with the alkali metals?  In this case the electron arrangement matches, but the chemical properties certainly don't.

Answer 3

It is a noble gas and has a full outer shell of electrons.