Which noble gas does not have a true octet

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.

14 days is the half-life of phosphorus-32