What is the three-dimensional shape of NH3?
The correct answer and explanation is:
Correct Answer: The three-dimensional shape of NH₃ (ammonia) is trigonal pyramidal.
Explanation (300 Words):
The three-dimensional shape of a molecule like ammonia (NH₃) is determined by the VSEPR theory (Valence Shell Electron Pair Repulsion theory), which states that electron pairs around a central atom will arrange themselves to be as far apart as possible to minimize repulsion.
In ammonia, the central atom is nitrogen (N). It forms three single covalent bonds with three hydrogen (H) atoms and has one lone pair of electrons. This gives nitrogen a total of four regions of electron density (three bonding pairs and one lone pair).
According to VSEPR theory, four regions of electron density arrange themselves in a tetrahedral electron geometry. However, because one of those regions is a lone pair (not bonded to another atom), the molecular geometry (the actual shape we see based on atoms alone) is trigonal pyramidal, not tetrahedral.
The lone pair of electrons exerts a slightly stronger repulsive force than the bonding pairs, pushing the hydrogen atoms down slightly and giving the molecule a pyramid-like shape. This also causes the H-N-H bond angles to shrink from the ideal tetrahedral angle of 109.5° to approximately 107°.
Additionally, the presence of a lone pair and the difference in electronegativity between nitrogen and hydrogen make NH₃ a polar molecule with a net dipole moment pointing from the hydrogen atoms toward the lone pair.
To summarize:
- Electron geometry: Tetrahedral
- Molecular shape: Trigonal pyramidal
- Bond angle: ~107°
- Polarity: Polar molecule
The trigonal pyramidal shape of NH₃ plays a significant role in its chemical behavior, including its basicity (ability to accept a proton) and its solubility in water.