Advanced Placement (AP) Chemistry Practice Exam

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Study for the AP Chemistry Exam with targeted quizzes and interactive questions. Gain expertise with detailed explanations for each question and boost your confidence before the test day!

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Which geometry describes a molecule with five electron pairs and no lone pairs?

Trigonal planar
Octahedral
Trigonal bipyramidal
Tetrahedral

The correct answer is: Trigonal bipyramidal

The correct choice is based on the arrangement of five electron pairs around a central atom and no lone pairs being present. When a central atom has five electron pairs, all of which are bonding pairs, the molecular geometry is described as trigonal bipyramidal. In a trigonal bipyramidal geometry, there are three electron pairs that occupy equatorial positions 120 degrees apart from one another, and two additional electron pairs that occupy axial positions, which are aligned along the vertical axis. This geometry allows for optimal spacing between the electron pairs to minimize repulsion according to VSEPR (Valence Shell Electron Pair Repulsion) theory. The other geometries listed do not apply to this specific arrangement: - Trigonal planar has three electron pairs and would suggest the absence of the axial pairs needed for a trigonal bipyramidal structure. - Octahedral geometry involves six electron pairs, which exceeds the number of electron pairs in this question. - Tetrahedral geometry corresponds to four electron pairs and would not adequately describe the presence of five pairs. Thus, trigonal bipyramidal is the geometry that accurately captures the arrangement of five bonding electron pairs around a central atom.