Answer:
The hydrogen molecule is the only one in which can not find an octet of electrons around each atom.
Explanation:
Let's evaluate each case.
1. Nitrogen (N₂):
With Z = 7, nitrogen has the following electronic configuration
1s²
2s² 2p³ → valence electrons
Since its valence electrons are 5, in the molecule one nitrogen atom shares 3 electrons with the other one, and each remains with an electron pair, so <u>each atom has an octet of electrons.</u>
2. Hydrogen (H₂):
With Z = 1, its electronic configuration is:
1s¹ → valence electron
In the molecule, the hydrogen atoms share the only electron they have, so they will have only 2 electrons around. In this diatomic molecule, <em><u>we can not find an octet.</u></em>
3. Oxygen (O₂):
Z = 8. Electronic configuration:
1s²
2s² 2p⁴ → valence electrons
In the diatomic molecule, each oxygen atom shares 2 electrons with the other one and remains with 2 pairs of electrons, therefore, <u>each oxygen atom has an octet</u>.
4. Fluorine (F₂)
Z = 9. Electronic configuration:
1s²
2s² 2p⁵ → valence electrons
In this molecule, each fluorine atom shares 1 electron with the other and remains with 3 pairs of electrons, hence, <u>each fluorine atom has an octet of electrons around</u>.
Finally, we can say that the hydrogen molecule is the only one in which can not find an octet of electrons around each atom.
I hope it helps you!
