Molecular structure worksheet - Molecular Structure Instructions ... - Free Printable

Problem Analysis:

The worksheet focuses on understanding molecular structures using the VSEPR (Valence Shell Electron Pair Repulsion) theory. The task involves analyzing the molecular geometry of different compounds by determining their Lewis structures, total electron domains, bonded atoms, lone pairs, and ultimately their molecular shapes.

Solution:

#### Review Questions:
1. Write a statement explaining which characteristics of an atom determine the VSEPR shape of a molecule.
- The VSEPR shape of a molecule is determined by the repulsion between electron pairs (both bonding and non-bonding) around the central atom. The key characteristics that influence the shape are:
- Total number of electron domains: This includes both bonding pairs and lone pairs.
- Number of bonded atoms: These are the atoms directly connected to the central atom.
- Number of lone pairs: These are the non-bonding electron pairs on the central atom.
- The goal is to minimize repulsion between these electron pairs, leading to specific geometries.

2. How does the force between the atoms impact the shape of a molecule?
- The force between atoms, primarily electrostatic repulsion, plays a crucial role in determining molecular shape. Electrons in bonding pairs and lone pairs repel each other due to their negative charges. This repulsion causes the electron pairs to arrange themselves as far apart as possible in three-dimensional space, resulting in specific molecular geometries. For example:
- Lone pairs repel more strongly than bonding pairs, leading to deviations from ideal geometries (e.g., bent shape in water).
- Bonding pairs also repel each other, but less strongly than lone pairs, influencing the overall shape.

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#### Activity: Filling in the Table

The table requires filling in the Lewis structure, VSEPR chart details, molecular shape, and drawing the VSEPR model for each compound. Let’s analyze each row step by step.

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##### Row 1: H₂O (Water)
- Compound: H₂O
- Lewis Structure:
- Central atom: Oxygen (O)
- Hydrogen atoms (H) are bonded to O.
- Oxygen has two lone pairs.
- Correct Lewis structure: `H-O-H` with two lone pairs on O.
- VSEPR Chart:
- Total Domains: 4 (2 bonding pairs + 2 lone pairs)
- Bonded Atoms: 2 (two H atoms)
- Lone Pairs: 2
- Molecular Shape:
- Electron Geometry: Tetrahedral (due to 4 total domains)
- Molecular Shape: Bent (due to 2 lone pairs causing distortion)
- VSEPR Model:
- Draw the molecule with a bent angle (~104.5°).

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##### Row 2: SiH₄ (Silane)
- Compound: SiH₄
- Lewis Structure:
- Central atom: Silicon (Si)
- Four hydrogen atoms (H) are bonded to Si.
- Silicon has no lone pairs.
- Correct Lewis structure: `H-Si-H` with all four H atoms bonded to Si.
- VSEPR Chart:
- Total Domains: 4 (4 bonding pairs)
- Bonded Atoms: 4 (four H atoms)
- Lone Pairs: 0
- Molecular Shape:
- Electron Geometry: Tetrahedral (due to 4 total domains)
- Molecular Shape: Tetrahedral (no lone pairs, so no distortion)
- VSEPR Model:
- Draw the molecule with a tetrahedral arrangement of H atoms around Si.

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##### Row 3: Br₂ (Bromine)
- Compound: Br₂
- Lewis Structure:
- Central atom: Bromine (Br)
- Two bromine atoms are bonded to each other.
- Each Br atom has three lone pairs.
- Correct Lewis structure: `Br-Br` with three lone pairs on each Br.
- VSEPR Chart:
- Total Domains: 2 (1 bonding pair + 1 lone pair per Br)
- Bonded Atoms: 2 (two Br atoms)
- Lone Pairs: 0 (considering only the central atom's perspective)
- Molecular Shape:
- Electron Geometry: Linear (due to 2 total domains)
- Molecular Shape: Linear (no lone pairs causing distortion)
- VSEPR Model:
- Draw the molecule as a straight line with a bond angle of 180°.

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Final Answer:

Here is the completed table:

| Compound | Draw Lewis Structure | Use VSEPR Chart to Determine: | Determine the Structures of the Molecule | Draw the VSEPR Model |
|----------|-----------------------|--------------------------------|-------------------------------------------|-----------------------|
| H₂O | `H-O-H` (with 2 lone pairs on O) | Total Domains: 4<br>Bonded Atoms: 2<br>Lone Pairs: 2 | Molecular Shape: Bent<br>Electron Geometry: Tetrahedral |  |
| SiH₄ | `H-Si-H` (all 4 H atoms bonded to Si) | Total Domains: 4<br>Bonded Atoms: 4<br>Lone Pairs: 0 | Molecular Shape: Tetrahedral<br>Electron Geometry: Tetrahedral |  |
| Br₂ | `Br-Br` (each Br has 3 lone pairs) | Total Domains: 2<br>Bonded Atoms: 2<br>Lone Pairs: 0 | Molecular Shape: Linear<br>Electron Geometry: Linear |  |

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Explanation of Drawings:

- H₂O: The molecule is bent due to the presence of two lone pairs on oxygen, which cause repulsion and distort the shape from tetrahedral to bent.
- SiH₄: The molecule is perfectly tetrahedral because there are no lone pairs on silicon, and all four electron domains are bonding pairs.
- Br₂: The molecule is linear because there are no lone pairs on the central bromine atom affecting the bond angle.

This completes the worksheet. If you have any further questions, feel free to ask!