Multiple Choice
Which term best describes the molecular geometry of the carbon dioxide (CO_2) molecule?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
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Which word or two-word phrase best describes the molecular geometry of the hydrogen cyanide (HCN) molecule?
A
Tetrahedral
B
Bent
C
Trigonal planar
D
Linear
Verified step by step guidance1
Identify the central atom in the HCN molecule, which is carbon (C), since hydrogen (H) and nitrogen (N) are bonded to it.
Determine the number of regions of electron density (bonding and lone pairs) around the central carbon atom. In HCN, carbon forms a single bond with hydrogen and a triple bond with nitrogen, so there are two regions of electron density.
Recall that molecular geometry depends on the arrangement of atoms around the central atom to minimize electron pair repulsion, according to VSEPR theory.
With two regions of electron density and no lone pairs on the central atom, the electron pairs arrange themselves 180° apart, resulting in a linear shape.
Therefore, the molecular geometry of HCN is best described as linear.
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