Molecular Shapes for Steric Numbers 2-4 (10.1.2) Flashcards
• 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.
• 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.
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 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 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.
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.
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.
SN = 2, 180° (A)
Which of the following has a trigonal planar electronic geometry?
CH2O (D)
Which steric number leads to the trigonal planar geometry, and what are the expected bond angles?
3, 120° (C)
Steric number 3 leads to a trigonal planar geometry with the three outer atoms arranged in a triangle and with the entire molecule arranged within one plane. The angle formed by these bonds is 120°, or 360° divided by 3.
What are the steric numbers for the central nitrogen atoms in these two molecules?
2, 2 (C)
Steric number is equal to the number of bonds (2, 2) plus the number of free electron pairs (0, 0) associated with the central atom (N).
Which of the following has a steric number of three and a bent molecular geometry?
O3 (D)
Ozone (O3 ) has a steric number of three and a bent molecular geometry. There are two atoms bonded to the central oxygen atom that also has one lone pair of electrons associated with it.
Which of the following molecules has only one lone pair on the central atom?
SO2 (B)
Sulfur dioxide (SO2 ) has a steric number of three and a bent shape. The bent shape (molecular geometry) is created for a molecule of steric number three when there is only one lone pair of electrons on the central atom of the molecule.
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.
SN = 2, 180° (C)
What is the bond angle of the H–S–H bond in a hydrogen sulfide molecule?
near 109.5° (B)
Hydrogen sulfide has a steric number of four and a tetrahedral (electronic) geometry. The tetrahedral geometry has a bond angle of 109.5°. Hydrogen sulfide also has two lone pairs of electrons on the central sulfur atom. These lone pairs will cause the H–S–H bond angle to be a little smaller than expected. Thus, the bond angle will be slightly less than 109.5°.
Which of the following does not have a linear molecular geometry?
SO2 (C)
Sulfur dioxide(SO2 ) has a steric number of three and one lone pair of electrons on the central sulfur atom. Sulfur dioxide has a bent shape (molecular geometry).
What is the shape (molecular geometry) of phosphorus trichloride (PCl3 )?
Trigonal pyramidal (C)
Phosphorus trichloride (PCl3 ) has a steric number of four and is based on the tetrahedral geometry. Because there is one lone pair of electrons on the central atom of the molecule, it has a trigonal pyramidal shape (molecular geometry).
