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Subject Test Chemistry

Question 11 of 17

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SAT Subject Test

Each of the questions or incomplete statements below is followed by five suggested answers or completions.  Select the one that is best in each case.

From their electron configurations, one can predict that the geometric configuration for which of the following molecules is NOT correct?

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text PF end text subscript 3 trigonal planar

Correct Answer: 
Yes

text CF end text subscript 4 tetrahedral

Correct Answer: 
No

text CHCl end text subscript 3 irregular tetrahedron

Correct Answer: 
No

text OF end text subscript 2 bent (v-shaped)

Correct Answer: 
No

text HF end text linear

Correct Answer: 
No

This is a question on chemical bonding that requires you to apply the principles of molecular bonding. Each of the molecules given is correctly paired with the term describing its molecular geometry except choice (A). The geometry of text PF end text text end text subscript 3 end subscript is not trigonal planar, but trigonal pyramidal because this geometry corresponds to a maximum possible separation of the electron pairs around the central atom, phosphorus, and therefore yields the most stable configuration. The central atom of the molecule is surrounded by the three single bonds and one unshared electron pair. Thus, the correct answer is choice (A). Note that this is the type of question that asks you to identify the one solution to the problem that is inappropriate.

Question Difficulty: 
medium