10.1.2 Molecular Shapes for Steric Numbers 2-4

Question 1

Molecular Shapes for Steric Numbers 2-4

Answer 1

• Knowing the Lewis dot structure of a molecule and the steric number (SN) of the central atom allows prediction of the shape and reactivity of that molecule.

Question 2

note

Answer 2

• Molecules with a steric number of 2 are built on the
  linear electronic geometry. These molecules have a linear molecular geometry (shape).
• The bond angle is 180° in molecules with SN 2.
• Molecules with a steric number of 3 are built on the trigonal planar electronic geometry. The bond angles are approximately 120° in molecules with SN 3.
• Molecules with SN 3 and no lone pairs have a
  trigonal planar molecular geometry.
• Molecules with SN 3 and one lone pair have a bent molecular geometry.
• Molecules with a steric number of 4 are built on the
  tetrahedral electronic geometry. The bond angles are
  approximately 109.5° in molecules with SN 4.
• Molecules with SN 4 and no lone pairs have a tetrahedral molecular geometry.
• Molecules with SN 4 and one lone pair have
  trigonal pyramidal molecular geometries.
• Molecules with SN 4 and two lone pairs have bent molecular geometries.

Question 3

What is the bond angle of the H–S–H bond in a hydrogen sulfide molecule?

Answer 3

near 109.5°

Question 4

Which of the following has a trigonal planar electronic geometry?

Answer 4

CH2O

Question 5

The picture shows one of the resonance structures for nitrous oxide (N2O). What is the steric number of the central nitrogen in this molecule, and what is the angle formed by the two bonds in the molecule.

Answer 5

SN = 2, 180°

Question 6

Which steric number leads to the trigonal planar geometry, and what are the expected bond angles?

Answer 6

3, 120°

Question 7

The picture shows carbon dioxide (CO2 ). What is the steric number of this molecule, and what is the angle formed by the two bonds in the molecule.

Answer 7

SN = 2, 180°

Question 8

What are the steric numbers for the central nitrogen atoms in these two molecules?

Answer 8

2, 2

Question 9

What is the shape (molecular geometry) of phosphorus trichloride (PCl3 )?

Answer 9

Trigonal pyramidal

Question 10

Which of the following does not have a linear molecular geometry?

Answer 10

SO2

Question 11

Which of the following has a steric number of three and a bent molecular geometry?

Answer 11

O3

Question 12

Which of the following molecules has only one lone pair on the central atom?

Answer 12

SO2