Answer:
Hellium
Explanation:
Data Given:
Krypton
Helium
Xenon
Neon
doesn't have true Octet =?
Solution:
Octet Rule:
The atoms have 8 electrons in their valence shell and have stable electronic configuration.
Now we will look for the electronic configuration of each given noble gas to look for octet rule
1. Krypton (Kr)
Atomic No. 36
Electrons per shell: 2, 8, 18, 8
Electronic configuration: [Ar] 3d¹⁰, 4s², 4p⁶
So
it have 8 electrons in its outer (valance) shell and obey octet rule
___________________
2. Hellium (He)
Atomic No. 2
Electrons per shell: 2
Electronic configuration: 1s²
So
It have 2 electrons in its outer (valance) shell and do not obey octet rule. although it is stable and obey duplet rule but not have true octet.
_____________________
3. Xenon (Xe)
Atomic No. 54
Electrons per shell: 2, 8, 18, 18, 8
Electronic configuration: [Kr] 4d¹⁰, 5s², 5p⁶
So
it have 8 electrons in its outer (valance) shell and obey octet rule
___________________
4. Neon (Ne)
Atomic No. 10
Electrons per shell: 2, 8
Electronic configuration: 1s², 2s², 2p⁶
So
it have 8 electrons in its outer (valance) shell and obey octet rule
___________________
So its only the hellium that do not have octet.
