Multiple Choice
Which of the following best explains why a water molecule (H_2O) has a bent geometry rather than a linear geometry?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
Multiple Choice
Which of the following molecules has a tetrahedral molecular geometry?
A
CO2
B
CH4
C
NH3
D
H2O
Verified step by step guidance1
Recall that molecular geometry depends on the arrangement of atoms around the central atom, which is determined by the number of bonding pairs and lone pairs of electrons according to the VSEPR (Valence Shell Electron Pair Repulsion) theory.
Identify the central atom and count the number of bonding pairs and lone pairs of electrons for each molecule:
- For CO2: The central atom is carbon, bonded to two oxygen atoms with no lone pairs on carbon.
- For CH4: The central atom is carbon, bonded to four hydrogen atoms with no lone pairs on carbon.
- For NH3: The central atom is nitrogen, bonded to three hydrogen atoms with one lone pair on nitrogen.
- For H2O: The central atom is oxygen, bonded to two hydrogen atoms with two lone pairs on oxygen.
Use the VSEPR model to determine the molecular geometry based on electron pairs:
- CO2 has two bonding pairs and no lone pairs, resulting in a linear geometry.
- CH4 has four bonding pairs and no lone pairs, resulting in a tetrahedral geometry.
- NH3 has three bonding pairs and one lone pair, resulting in a trigonal pyramidal geometry.
- H2O has two bonding pairs and two lone pairs, resulting in a bent (angular) geometry.
Conclude that the molecule with a tetrahedral molecular geometry is the one with four bonding pairs and no lone pairs on the central atom, which is CH4.
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