How many unpaired electrons are present in `Ni^(2+)` cation? (At. No. = 28)

Options

A. 0
B. 2
C. 4
D. 6

Explanation

To determine the number of unpaired electrons in the `Ni^(2+)` cation, we will follow these steps:

### Step 1: Determine the Atomic Number and Electron Configuration of Nickel
Nickel (Ni) has an atomic number of 28. The electron configuration of a neutral nickel atom is:
\[ \text{Ni: } [\text{Ar}] \, 3d^8 \, 4s^2 \]
This means that nickel has 8 electrons in the 3d subshell and 2 electrons in the 4s subshell.

**Hint:** Remember that the electron configuration is built by filling the lowest energy orbitals first.

### Step 2: Remove Electrons to Form the `Ni^(2+)` Cation
To form the `Ni^(2+)` cation, we need to remove 2 electrons. Electrons are removed first from the 4s subshell before the 3d subshell. Therefore, the electron configuration for `Ni^(2+)` will be:
\[ \text{Ni}^{2+}: [\text{Ar}] \, 3d^8 \, 4s^0 \]
This indicates that there are no electrons in the 4s subshell and 8 electrons in the 3d subshell.

**Hint:** When forming cations, always remove electrons from the outermost shell first.

### Step 3: Distribute the 3d Electrons into Orbitals
The 3d subshell can hold a maximum of 10 electrons and consists of 5 orbitals. We will distribute the 8 electrons among these 5 orbitals. The filling of the 3d orbitals follows Hund's rule, which states that electrons will fill degenerate orbitals singly before pairing up.

1. Fill the first five orbitals with one electron each:
- Orbital 1: ↑
- Orbital 2: ↑
- Orbital 3: ↑
- Orbital 4: ↑
- Orbital 5: ↑

2. Now, we have 3 electrons left to place. We will start pairing them:
- Orbital 1: ↑↓
- Orbital 2: ↑↓
- Orbital 3: ↑
- Orbital 4: ↑
- Orbital 5: ↑

**Hint:** Remember that each orbital can hold a maximum of 2 electrons, and fill singly before pairing.

### Step 4: Count the Unpaired Electrons
From the distribution above, we can see that:
- Orbital 1 has 2 electrons (paired).
- Orbital 2 has 2 electrons (paired).
- Orbital 3 has 1 electron (unpaired).
- Orbital 4 has 1 electron (unpaired).
- Orbital 5 has 1 electron (unpaired).

Thus, there are **3 unpaired electrons** in the `Ni^(2+)` cation.

**Final Answer:** The number of unpaired electrons in `Ni^(2+)` is **2**.