Number of unpaired electrons in K2[NiF6]

Explanation:

1. Understanding the structure of K2[NiF6]
K2[NiF6] is the chemical formula for potassium hexafluoroniobate. It consists of potassium cations (K+) and the hexafluoroniobate anion ([NiF6]2-). The [NiF6]2- anion contains a central nickel atom (Ni) surrounded by six fluoride ions (F-).

2. Determining the electron configuration of Ni
To determine the number of unpaired electrons in Ni, we need to know its electron configuration. The atomic number of Ni is 28, so its electron configuration can be written as [Ar] 3d8 4s2. The [Ar] represents the electron configuration of argon (the noble gas before Ni in the periodic table).

3. Analyzing the d-orbitals of Ni
In the electron configuration of Ni, the 3d orbital is partially filled with 8 electrons. The d-orbitals can hold a maximum of 10 electrons. Since there are only 8 electrons in the 3d orbital of Ni, there are two empty d-orbitals available for bonding.

4. Applying Hund's Rule
Hund's rule states that electrons occupy orbitals of the same energy level singly, with the same spin, before pairing up. In other words, electrons prefer to occupy separate orbitals before pairing.

5. Determining the number of unpaired electrons
Since there are two empty d-orbitals available in the 3d orbital of Ni, all the electrons in the 3d orbital will be unpaired. Therefore, the number of unpaired electrons in Ni is 2.

6. Considering the overall compound
In K2[NiF6], there are two potassium cations (K+) and one hexafluoroniobate anion ([NiF6]2-). The overall charge of the compound must be neutral, so the number of positive charges from the potassium cations must balance the negative charge from the anion.

7. Final answer
Since the [NiF6]2- anion has a charge of 2-, and each potassium cation has a charge of +1, it takes two potassium cations to balance the charge of the anion. Therefore, the overall compound has a neutral charge, and the number of unpaired electrons in K2[NiF6] is 0.