Draw the structure and predict the molecular geometry for NH3. What do the geometries of these molecules have in common? How would the bond angles compare
The Correct Answer and Explanation is:
Structure and Molecular Geometry of NH₃ (Ammonia)
1. Lewis Structure:
- Nitrogen (N) has 5 valence electrons, and each hydrogen (H) atom has 1 valence electron.
- In NH₃, nitrogen shares electrons with three hydrogen atoms, forming three N-H bonds.
- Nitrogen has a lone pair of electrons that occupies one of the positions in the valence shell.
The Lewis structure is as follows:
H
|
H - N - H
|
lone pair
2. Electron Geometry:
- The electron geometry around nitrogen is tetrahedral since nitrogen has three bonding pairs and one lone pair of electrons, making a total of four regions of electron density.
3. Molecular Geometry:
- The presence of the lone pair on nitrogen alters the shape of the molecule. This results in a trigonal pyramidal molecular geometry.
- The lone pair repels the bonding pairs, causing the H-N-H bond angles to be slightly less than the ideal 109.5° of a perfect tetrahedral structure.
Bond Angles:
- In NH₃, the bond angles between the hydrogen atoms (H-N-H) are approximately 107°, which is slightly less than the ideal 109.5° due to the lone pair occupying more space and causing increased repulsion on the bonding pairs.
Commonality in Geometries:
- Both NH₃ and molecules with similar structures (e.g., H₂O) have trigonal pyramidal geometries due to the lone pairs on the central atom.
- For example, H₂O has a bent molecular geometry due to two lone pairs on oxygen, while NH₃ has a trigonal pyramidal geometry with one lone pair on nitrogen.
Comparison of Bond Angles:
- Both NH₃ and H₂O show bond angles that are less than 109.5° because the lone pairs cause greater electron repulsion.
- NH₃ has bond angles around 107°, while H₂O has even smaller bond angles (104.5°) because of two lone pairs.
In summary, molecules like NH₃ and H₂O share a common trait of having lone pairs that reduce their bond angles from the ideal tetrahedral angle of 109.5°. This results in trigonal pyramidal and bent molecular geometries, respectively.
