Introduction to VSEPR Theory and molecular shape

Which of the following best describes the shape of a molecule with two bonding pairs and no lone pairs on the central atom according to VSEPR theory?

• Trigonal planar

• Linear

• Tetrahedral

• Bent

Answer explanation

According to VSEPR theory, a molecule with two bonding pairs and no lone pairs on the central atom adopts a linear shape. This arrangement minimizes repulsion between the bonding pairs, resulting in a straight line.

What is the bond angle in a perfect tetrahedral molecule?

Answer explanation

In a perfect tetrahedral molecule, the bond angles are approximately 109.5°. This geometry arises from the repulsion between four equivalent bonding pairs of electrons, maximizing their distance from each other.

• Linear

• Trigonal planar

• Trigonal pyramidal

• Tetrahedral

Answer explanation

Ammonia (NH3) has a central nitrogen atom bonded to three hydrogen atoms and one lone pair of electrons. This arrangement leads to a trigonal pyramidal geometry due to the repulsion between the lone pair and bonding pairs.

What is the bond angle in a molecule with a trigonal planar geometry?

Answer explanation

In a trigonal planar geometry, the bond angles are 120 degrees. This arrangement allows for optimal spacing between the three bonding pairs of electrons, minimizing repulsion according to VSEPR theory.

Which of the following molecules has a bent shape?

Answer explanation

The molecule H₂O has a bent shape due to the two lone pairs on the oxygen atom, which repel the hydrogen atoms. In contrast, CO₂, CH₄, and BF₃ have linear or trigonal planar shapes.

• 0

• 1

• 2

• 4

Answer explanation

In the linear molecule CO₂, the central carbon atom forms two double bonds with oxygen atoms. Since all valence electrons are used in bonding, there are 0 lone pairs on the central atom.

• Tetrahedral

• Trigonal planar

• Trigonal pyramidal

• Bent

Answer explanation

The geometry of BF₃ is trigonal planar because it has three bonding pairs of electrons around the central boron atom and no lone pairs, resulting in a flat, triangular shape.

What is the expected bond angle in a molecule with a linear geometry?

Answer explanation

In a linear geometry, the atoms are arranged in a straight line, resulting in a bond angle of 180°. This is characteristic of molecules like CO2, where the two bonds are opposite each other.

Which of the following molecules has a trigonal pyramidal shape?

Answer explanation

The molecule NH₃ (ammonia) has a trigonal pyramidal shape due to the presence of one lone pair of electrons on the nitrogen atom, which pushes the hydrogen atoms down, creating a pyramid-like structure.

• Linear

• Trigonal planar

• Tetrahedral

• Bent

Answer explanation

The molecular geometry of CH₄ (methane) is tetrahedral because it has four hydrogen atoms bonded to a central carbon atom, with bond angles of approximately 109.5 degrees, resulting in a three-dimensional shape.