What is covalency of chlorine atom in second excited state ?

Answer

To determine the covalency of a chlorine atom in its second excited state, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Covalency**:
Covalency refers to the number of unpaired electrons in an atom that can participate in bonding. It is essentially the number of electrons an atom can share with other atoms.

**Hint**: Remember that covalency is linked to the number of unpaired electrons available for bonding.

2. **Determine the Atomic Number and Electronic Configuration of Chlorine**:
Chlorine has an atomic number of 17, which means it has 17 electrons. The electronic configuration of chlorine is:
\[ 1s^2, 2s^2, 2p^6, 3s^2, 3p^5 \]
This shows that in the outermost shell (n=3), chlorine has 5 electrons in the 3p subshell and 2 electrons in the 3s subshell.

**Hint**: Write down the electronic configuration to visualize the distribution of electrons.

3. **Identify the Ground State Configuration**:
In the ground state, chlorine has 5 electrons in the 3p subshell and 2 in the 3s subshell. The 3d subshell is empty.

**Hint**: Recognize that the outermost shell's electrons are crucial for determining covalency.

4. **Excitation of Electrons**:
In the first excited state, one electron from the 3p subshell can be promoted to the empty 3d subshell. This results in:
\[ 3s^2, 3p^4, 3d^1 \]
Here, there are 4 electrons in the 3p subshell and 1 in the 3d subshell.

**Hint**: Understand that excitation involves moving electrons to higher energy levels.

5. **Second Excited State**:
In the second excited state, another electron from the 3p subshell can be promoted to the 3d subshell. This results in:
\[ 3s^2, 3p^3, 3d^2 \]
Now, there are 3 unpaired electrons in the 3p subshell and 2 in the 3d subshell.

**Hint**: Track the movement of electrons carefully to see how the number of unpaired electrons changes.

6. **Count Unpaired Electrons**:
In the second excited state, the number of unpaired electrons is:
- 3 unpaired electrons in the 3p subshell
- 2 unpaired electrons in the 3d subshell
Therefore, the total number of unpaired electrons (covalency) is:
\[ 3 + 2 = 5 \]

**Hint**: Add the unpaired electrons from all relevant subshells to find the total covalency.

### Final Answer:
The covalency of a chlorine atom in its second excited state is **5**.