Why is helium considered a noble gas?
2 answers
The noble gases are found in group 18 of the periodic table. These elements were considered to be inert gases until the 1960's, because their oxidation number of 0 prevents the noble gases from forming compounds readily. All noble gases have the maximum number of electrons possible in their outer shell. Here Helium has 2 electrons in their outer shells while other noble gases have 8 in their outer shells. That is why they are stable and considered to be a noble gas.
Two comments:
1. How in the world did this get named as a question in organic chemistry. Helium is about as un-organic as you can get.
2. With regard to Yang's answer. That's a great answer EXCEPT that "all noble gases have the maximum number of electrons possible in their outer shell." That isn't quite true since the third shell can hold 18, 32, etc from 2N^2. (It's that word "possible" that bugs me.") Yes, all noble gases have 8 electrons in their outside shell but that shell may hold many more electrons except for He and Ne. And yes, I know I'm being picky.
1. How in the world did this get named as a question in organic chemistry. Helium is about as un-organic as you can get.
2. With regard to Yang's answer. That's a great answer EXCEPT that "all noble gases have the maximum number of electrons possible in their outer shell." That isn't quite true since the third shell can hold 18, 32, etc from 2N^2. (It's that word "possible" that bugs me.") Yes, all noble gases have 8 electrons in their outside shell but that shell may hold many more electrons except for He and Ne. And yes, I know I'm being picky.