How many lone pairs of electrons does the Lewis dot structure of H2Se have around its central atom and what is the shape of the molecule? A. 2, tetrahedral B. 2, bent C. 1, triangular planar D. 0, linear
The correct answer and explanation is:
Correct Answer: B. 2, bent
Explanation:
To determine the number of lone pairs around the central atom and the shape of the molecule H₂Se (hydrogen selenide), we follow these steps:
1. Determine the total number of valence electrons:
- Hydrogen (H): 1 valence electron × 2 = 2
- Selenium (Se): Group 16 element = 6 valence electrons
Total = 2 + 6 = 8 valence electrons
2. Draw the Lewis structure:
- Place Se as the central atom.
- Attach 2 hydrogen atoms to Se using single bonds.
- Each single bond uses 2 electrons, so 2 × 2 = 4 electrons are used.
- This leaves 8 – 4 = 4 electrons, or 2 lone pairs, which are placed on the Se atom.
So, the Lewis structure has:
- 2 bonding pairs (H–Se–H)
- 2 lone pairs on Se
3. Determine the molecular shape (VSEPR theory):
The electron pair geometry is based on four regions of electron density (2 bonds + 2 lone pairs) around Se, which corresponds to a tetrahedral electron geometry.
However, lone pairs do not count toward the molecular shape—only the atoms do. With only two atoms bonded to Se, and two lone pairs, the molecular shape is:
👉 Bent
4. Final Answer:
- Number of lone pairs around Se: 2
- Molecular shape: Bent
So, H₂Se is a bent molecule with two lone pairs on selenium. This bent shape gives H₂Se polar properties and a similar geometry to H₂O, due to the same electron pair distribution around the central atom.
✅ Answer: B. 2, bent