Question

Which of the following molecules has a trigonal planar shape?

• A. \( \mathrm{CH_4} \)
• B. \( \mathrm{BF_3} \)
• C. \( \mathrm{NH_3} \)
• D. \( \mathrm{H_2O} \)

Hint:

Tip: Use VSEPR theory to determine molecular shape based on bonding and lone pairs.

Answer 1

The Correct Option is B

To identify the molecule with a trigonal planar shape, we must first understand molecular geometry. Molecular shape is dictated by the arrangement of atoms around the central atom, governed by electron-pair repulsion principles as described by VSEPR (Valence Shell Electron Pair Repulsion) theory.

VSEPR Theory: The spatial arrangement of valence electron pairs around a central atom minimizes repulsion. This arrangement determines the molecule's shape.

Molecule	Chemical Formula	Geometry
Methane	\( \mathrm{CH_4} \)	Tetrahedral
Boron Trifluoride	\( \mathrm{BF_3} \)	Trigonal Planar
Ammonia	\( \mathrm{NH_3} \)	Trigonal Pyramidal
Water	\( \mathrm{H_2O} \)	Bent

Analysis of each molecule's geometry:

• \( \mathrm{CH_4} \): Methane exhibits a tetrahedral geometry due to the central carbon atom bonded to four hydrogen atoms, with no lone pairs.
• \( \mathrm{BF_3} \): Boron trifluoride possesses a trigonal planar shape. This arises from the central boron atom being bonded to three fluorine atoms, with no lone pairs on boron.
• \( \mathrm{NH_3} \): Ammonia adopts a trigonal pyramidal geometry. The central nitrogen atom is bonded to three hydrogen atoms and has one lone pair of electrons.
• \( \mathrm{H_2O} \): Water's bent shape results from the oxygen atom bonded to two hydrogen atoms and possessing two lone pairs of electrons.

Consequently, the molecule with the trigonal planar shape is \( \mathrm{BF_3} \).