- The outer electron shell is a part of the electron configuration
- Elements in group 18 have full / complete outer electron shells on the periodic table of elements
- Therefore, elements in group 18 have similar electron configuration

- Elements in group 18 have similar electron configuration
- If the elements have similar electron configurations , then the elements will be grouped into same family / group on the periodic table of elements
- So, elements in group 18 are grouped together because they have similar electron configuration

So, elements in group 18 are grouped together because they have similar electron configuration
Q: On the periodic table, the elements in group 18 (8A) (helium, neon, argon, etc.) are grouped together because
Context:
- If the elements have similar electron configurations , then the elements will be grouped into same family / group on the periodic table of elements 
- The outer electron shell is a part of the electron configuration 
- Elements in group 18 have full / complete outer electron shells on the periodic table of elements