📚 Electron Domain Geometries Explained
Electron domain geometry focuses on the arrangement of all electron domains (bonds and lone pairs) around a central atom. It's the foundation for understanding molecular shapes.
🧪 Linear Geometry
- ⚛️ A molecule is linear when the central atom is bonded to two other atoms, and there are no lone pairs on the central atom.
- 📐 The bond angle is 180°.
- 📝 Example: $CO_2$. Carbon is double-bonded to two oxygen atoms ($O=C=O$).
📐 Trigonal Planar Geometry
- ⚛️ A molecule exhibits trigonal planar geometry when the central atom is bonded to three other atoms, and there are no lone pairs on the central atom.
- 📐 The bond angles are 120°.
- 📝 Example: $BF_3$. Boron is bonded to three fluorine atoms.
SixElectron Geometry
- ⚛️ A molecule exhibits tetrahedral geometry when the central atom is bonded to four other atoms, and there are no lone pairs on the central atom.
- 📐 The bond angles are approximately 109.5°.
- 📝 Example: $CH_4$. Carbon is bonded to four hydrogen atoms.
💡 Key Differences & Summary
The key difference lies in the number of atoms bonded to the central atom and the presence/absence of lone pairs. Here's a table summarizing the geometries:
| Geometry |
Bonded Atoms |
Lone Pairs |
Bond Angle(s) |
Example |
| Linear |
2 |
0 |
180° |
$CO_2$ |
| Trigonal Planar |
3 |
0 |
120° |
$BF_3$ |
| Tetrahedral |
4 |
0 |
109.5° |
$CH_4$ |
📝 Practice Quiz
Identify the electron domain geometry of the central atom in each of the following molecules:
- $BeCl_2$
- $SO_3$
- $CCl_4$
- $H_2O$ (Hint: consider lone pairs on oxygen)
- $BH_3$
Answers: 1. Linear, 2. Trigonal Planar, 3. Tetrahedral, 4. Tetrahedral (bent molecular shape), 5. Trigonal Planar