Write the outer shell configuration of atomic number 31.

Answer

To find the outer shell configuration of an element with atomic number 31, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Number**: The atomic number given is 31. This means we are looking for the electron configuration of the element with 31 electrons.

2. **Determine the Period**:
- The atomic number helps us identify the period of the element.
- Elements are arranged in periods based on their electron configurations.
- The first 18 atomic numbers correspond to the first three periods (1-2 for the first period, 3-10 for the second period, and 11-18 for the third period).
- The next period starts from atomic number 19. Since 31 is greater than 18, it lies in the 4th period.

3. **Identify the Group**:
- The group can be determined by finding how many electrons are in the outermost shell.
- The 4th period includes elements from atomic number 19 (K) to 36 (Kr).
- The element with atomic number 31 is Gallium (Ga), which is in group 13.

4. **Write the General Electron Configuration**:
- For group 13 elements, the general electron configuration can be expressed as \( ns^2 np^1 \), where n is the period number.
- Since we are in the 4th period (n=4), we can substitute n with 4.

5. **Determine the Specific Configuration**:
- The outer shell configuration for Gallium will be \( 4s^2 \) and \( 4p^1 \).
- Therefore, the outer shell configuration of atomic number 31 is \( 4s^2 4p^1 \).

### Final Answer:
The outer shell configuration of atomic number 31 is \( 4s^2 4p^1 \).

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