Predict the molecular shape of these compounds. ammonia, NH3 H- linear trigonal pyramidal tetrahedral -H trigonal planar (120°) bent beryllium fluoride, BeF2 bent linear Be- -F: trigonal planar (120°) trigonal pyramidal tetrahedral ammonium, NH4+ + linear trigonal pyramidal bent trigonal planar (120°) tetrahedral hydrogen sulfide, H2S HSH trigonal planar (120°) bent trigonal pyramidal tetrahedral linear
The Correct Answer and Explanation is :
To predict the molecular shape of the compounds mentioned—ammonia (NH3), beryllium fluoride (BeF2), ammonium (NH4+), and hydrogen sulfide (H2S)—we’ll use the VSEPR (Valence Shell Electron Pair Repulsion) theory. This theory states that electron groups around a central atom will arrange themselves to minimize repulsion, influencing the molecular shape.
Ammonia (NH3)
- Electron Groups: 4 (3 bonding pairs, 1 lone pair)
- Molecular Geometry: Trigonal pyramidal
- Reasoning: Ammonia has three hydrogen atoms bonded to a central nitrogen atom, with one lone pair of electrons on the nitrogen. The lone pair contributes to the electron count but does not affect the visible shape, making the molecule adopt a trigonal pyramidal structure.
Beryllium Fluoride (BeF2)
- Electron Groups: 2 (2 bonding pairs)
- Molecular Geometry: Linear
- Reasoning: Beryllium fluoride has two fluorine atoms bonded to a central beryllium atom. There are no lone pairs on beryllium, leading to a straightforward linear arrangement due to the two electron groups trying to stay as far apart as possible.
Ammonium (NH4+)
- Electron Groups: 4 (4 bonding pairs)
- Molecular Geometry: Tetrahedral
- Reasoning: The ammonium ion consists of four hydrogen atoms bonded to a central nitrogen atom. The positive charge indicates an additional proton, but there are still no lone pairs on nitrogen, resulting in a symmetric tetrahedral shape.
Hydrogen Sulfide (H2S)
- Electron Groups: 4 (2 bonding pairs, 2 lone pairs)
- Molecular Geometry: Bent
- Reasoning: Hydrogen sulfide has two hydrogen atoms bonded to a central sulfur atom, which also has two lone pairs of electrons. This configuration forces the molecule into a bent shape due to the repulsion between the lone pairs and the bonding pairs.
Summary
Each molecule’s geometry results from minimizing the repulsion between both the bonding pairs and lone pairs of electrons around the central atom:
- NH3 is trigonal pyramidal due to one lone pair affecting the arrangement of three bonding pairs.
- BeF2 is linear, lacking lone pairs and having only two bonding pairs.
- NH4+ is tetrahedral, with four bonding pairs and no lone pairs influencing its shape.
- H2S is bent, significantly influenced by its two lone pairs along with two bonding pairs.
Understanding these geometries provides insights into each molecule’s chemical properties and interactions, such as bonding tendencies, polarity, and reactivity.