Total number of unpaired electrons in an atom of atomic number 29 is

Options

A. 1
B. 3
C. 4
D. 2

Explanation

To determine the total number of unpaired electrons in an atom with atomic number 29 (which is copper), we need to follow these steps:

### Step 1: Identify the Element
The atomic number 29 corresponds to the element copper (Cu).

### Step 2: Write the Electronic Configuration
Using the Aufbau principle, we fill the orbitals in order of increasing energy levels. The electronic configuration of copper (Cu) is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁹

### Step 3: Adjust for Stability
Copper is an exception to the expected electron configuration due to stability reasons. Instead of having a configuration of 4s² 3d⁹, copper donates one electron from the 4s orbital to the 3d orbital to achieve a more stable configuration. Thus, the correct configuration becomes:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

### Step 4: Count Unpaired Electrons
Now, we analyze the orbitals:
- In the 4s orbital, there is **1 electron** (which is unpaired).
- In the 3d orbital, there are **10 electrons**. The 3d subshell can hold a maximum of 10 electrons and is completely filled, meaning there are **no unpaired electrons** in the 3d subshell.

### Step 5: Total Unpaired Electrons
Adding the unpaired electrons from both orbitals:
- 4s: 1 unpaired electron
- 3d: 0 unpaired electrons

Thus, the total number of unpaired electrons in a copper atom (atomic number 29) is **1**.

### Final Answer
The total number of unpaired electrons in an atom of atomic number 29 (copper) is **1**.

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