Report atomic number of the element having largest size among the following: `Ni, Cu, Zn`

Answer

To determine the atomic number of the element with the largest atomic size among Nickel (Ni), Copper (Cu), and Zinc (Zn), we can follow these steps:

### Step 1: Write the electronic configurations of the elements.
- **Nickel (Ni)**: The atomic number of Nickel is 28. Its electronic configuration is:
\[ \text{Ni: } [\text{Ar}] \, 4s^2 \, 3d^8 \]

- **Copper (Cu)**: The atomic number of Copper is 29. Its electronic configuration is:
\[ \text{Cu: } [\text{Ar}] \, 4s^1 \, 3d^{10} \]

- **Zinc (Zn)**: The atomic number of Zinc is 30. Its electronic configuration is:
\[ \text{Zn: } [\text{Ar}] \, 4s^2 \, 3d^{10} \]

### Step 2: Analyze the atomic size trend.
- Atomic size generally increases down a group in the periodic table and decreases across a period from left to right. However, for transition metals, the trend can be influenced by the effective nuclear charge and electron shielding.

### Step 3: Compare the effective nuclear charge and shielding effect.
- **Zinc (Zn)** has a full 3d subshell (10 electrons) and two electrons in the 4s subshell. The effective nuclear charge (Z_eff) experienced by the outer electrons is reduced due to the shielding effect of the inner electrons.

- **Copper (Cu)** has a similar configuration but with only one electron in the 4s subshell and a fully filled 3d subshell. The shielding effect is less compared to Zinc.

- **Nickel (Ni)** has a partially filled 3d subshell (8 electrons) and two electrons in the 4s subshell, which also contributes to a relatively higher Z_eff compared to Zinc.

### Step 4: Conclusion on atomic size.
- Due to the greater shielding effect in Zinc (Zn) compared to Nickel (Ni) and Copper (Cu), Zinc has the largest atomic size among the three elements.

### Step 5: Report the atomic number of the element with the largest size.
- Therefore, the element with the largest size is Zinc, and its atomic number is:
\[ \text{Atomic Number of Zinc (Zn) = 30} \]

### Final Answer:
The atomic number of the element having the largest size among Ni, Cu, and Zn is **30** (Zinc).

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