Question

Total number of electrons present around the central atom in order of \( \text{PCl}_5 \), \( \text{SF}_6 \), \( \text{SCl}_2 \)

Hint:

A quick shortcut formula for total electrons around a central atom:
Total $e^-$ = (Number of valence $e^-$ of central atom) + (Number of monovalent atoms attached) - (Charge). For $\text{PCl}_5$: $5 + 5 = 10$. For $\text{SF}_6$: $6 + 6 = 12$. For $\text{SCl}_2$: $6 + 2 = 8$.

Answer 1

Step 1: Understanding the Concept:
To find the total number of electrons around a central atom in a molecule, we need to draw its Lewis dot structure and count the valence electrons surrounding it. This includes all electrons shared in bonds (2 electrons per single bond) plus any unshared non-bonding electrons (lone pairs).

Step 2: Key Formula or Approach:
For each molecule:
1. Identify the central atom and its number of valence electrons.
2. Determine the number of single bonds formed with surrounding atoms.
3. Calculate remaining lone pair electrons on the central atom.
4. Total electrons = (Number of bonds $\times$ 2) + (Number of lone pair electrons).

Step 3: Detailed Explanation:
Let's analyze each molecule:
1. $\text{PCl}_5$ (Phosphorus pentachloride):
- Central atom: Phosphorus (P), Group 15 $\rightarrow$ 5 valence electrons.
- It forms 5 single bonds with 5 Chlorine atoms.
- All 5 valence electrons are used in bonding. Lone pairs = 0.
- Total electrons = $5 \text{ bonds} \times 2 \text{ e}^-/\text{bond} = 10$ electrons.
(Note: This is an expanded octet).
2.
- Central atom: Sulfur (S), Group 16 $\rightarrow$ 6 valence electrons.
- It forms 6 single bonds with 6 Fluorine atoms.
- All 6 valence electrons are used in bonding. Lone pairs = 0.
- Total electrons = $6 \text{ bonds} \times 2 \text{ e}^-/\text{bond} = 12$ electrons.
(Note: This is an expanded octet).
3. $\text{SCl}_2$ (Sulfur dichloride):
- Central atom: Sulfur (S), Group 16 $\rightarrow$ 6 valence electrons.
- It forms 2 single bonds with 2 Chlorine atoms (using 2 valence electrons).
- Remaining valence electrons on S = $6 - 2 = 4$ electrons (which is 2 lone pairs).
- Total electrons around S = (2 bonding pairs $\times$ 2) + 4 lone pair electrons = $4 + 4 = 8$ electrons.

Listing them in the requested order: 10, 12, 8.

Step 4: Final Answer:
The total number of electrons are 10, 12, and 8 respectively.