Final Answer:
A molecule with the same number of electrons as the azide ion (N₃⁻) is cyanate (NCO⁻).
Step-by-step explanation:
The azide ion (N₃⁻) has 7 electrons contributed by each nitrogen atom (5 valence electrons + 2 gained electrons) for a total of 21 electrons. To find a molecule with the same number of electrons, we need an element with one fewer electron. Cyanate (NCO⁻) fits this criterion. Each nitrogen contributes 5 electrons, and the carbon and oxygen each contribute 6 and 6 electrons, respectively. Adding these together gives us a total of 21 electrons, mirroring the electron count in the azide ion.
In detail, nitrogen has 5 valence electrons, carbon has 4 valence electrons, and oxygen has 6 valence electrons. The negative charge on the cyanate ion indicates an additional electron. Therefore, the nitrogen contributes 5 electrons, the carbon contributes 5 electrons (4 from valence + 1 from the additional electron), and the oxygen contributes 7 electrons (6 from valence + 1 from the additional electron). Adding these up results in a total of 21 electrons, making cyanate isoelectronic with the azide ion.
This similarity in electron count is crucial because it determines the chemical behavior of these species. Molecules with the same number of electrons often exhibit similar properties due to comparable electronic structures, influencing their reactivity and bonding patterns.