Molecular Symmetry & Point groups

Question 1

What is symmetry?

Answer 1

Symmetry is a property of molecules containing more than one atom of the same kind, with equal
bond lengths and/or bond angles.

Question 2

True or False: Symmetry in molecules can affect their physical and chemical properties.

Answer 2

True

Question 3

What is a point group?

Answer 3

A set of symmetry operations that describe the symmetry of a molecule.

Question 4

Fill in the blank: The simplest point group is ______.

Answer 4

C1

Question 5

What does the ‘C’ in ‘Cn’ point groups represent?

Answer 5

Rotation axis

Question 6

List the types of symmetry operations in molecular symmetry.

Answer 6

Rotation, reflection, inversion, improper rotation

Question 7

What is the significance of the principal axis in point groups?

Answer 7

It is the axis with the highest order of rotation.

Question 8

Multiple choice: Which of the following is a point group? A) C2v B) C3h C) D4d D) All of the above

Answer 8

D) All of the above

Question 9

What is an improper rotation?

Answer 9

A rotation followed by a reflection through a plane perpendicular to the rotation axis.

Question 10

True or False: A molecule with no symmetry elements belongs to the point group C1.

Answer 10

True

Question 11

What is the symmetry element for a mirror plane?

Answer 11

Reflection plane

Question 12

Fill in the blank: The point group Dnh is characterized by ______.

Answer 12

A principal rotation axis and n vertical mirror planes

Question 13

What is the role of symmetry in spectroscopy?

Answer 13

It helps predict the selection rules for transitions.

Question 14

Multiple choice: Which point group has only one symmetry element? A) C1 B) C2 C) D2h D) C∞v

Answer 14

A) C1

Question 15

What does the ‘h’ in ‘Dnh’ indicate?

Answer 15

Presence of horizontal mirror plane

Question 16

What is the relationship between symmetry and chirality?

Answer 16

Chiral molecules lack symmetry elements that relate them to their mirror images.

Question 17

True or False: All molecules with a center of inversion are achiral.

Answer 17

True

Question 18

What is the character table used for?

Answer 18

It summarizes the symmetry properties of a point group.

Question 19

Fill in the blank: The point group C∞v is associated with ______.

Answer 19

Linear molecules

Question 20

What is the effect of symmetry on molecular vibrations?

Answer 20

Symmetry determines the number of active vibrations and their selection rules.

Question 21

Multiple choice: Which of the following molecules belongs to the point group D2h? A) H2O B) CO2 C) NH3 D) CH4

Answer 21

B) CO2

Question 22

What is a symmetry operation?

Answer 22

An action that moves a molecule into an equivalent configuration.

Question 23

True or False: The identity operation is always a part of every point group.

Answer 23

True

Question 24

What is the significance of the order of a point group?

Answer 24

It indicates the number of symmetry operations in the group.

Question 25

Fill in the blank: A molecule with a single C3 axis and three vertical planes belongs to the point group ______.

Answer 25

C3v

Question 26

What is a point group in inorganic chemistry?

Answer 26

A point group is a set of symmetry operations that leave at least one point in the molecule unchanged.

Question 27

True or False: All molecules belong to a point group.

Answer 27

True

Question 28

Which point group does a molecule with a C2 rotational axis and two vertical planes of symmetry belong to?

Answer 28

C2v

Question 29

Fill in the blank: The point group for a linear molecule like carbon dioxide (CO2) is ____.

Answer 29

D∞h

Question 30

What symmetry operation is represented by the symbol 'σ'?

Answer 30

Reflection

Question 31

Identify the point group for a tetrahedral molecule.

Answer 31

T

Question 32

Which point group is associated with molecules that have a center of inversion?

Answer 32

i

Question 33

True or False: The point group C3 has three symmetry operations.

Answer 33

False

Question 34

What is the point group of ammonia (NH3)?

Answer 34

C3v

Question 35

Which point group does benzene (C6H6) belong to?

Answer 35

D6h

Question 36

Multiple Choice: Which of the following molecules belongs to the point group C2h? A) H2O B) NH3 C) Ethylene D) Cyclobutane

Answer 36

C) Ethylene

Question 37

What type of symmetry operation is a 'C3' rotation?

Answer 37

Rotation by 120 degrees around an axis

Question 38

Fill in the blank: The point group for a square planar molecule like xenon tetrafluoride (XeF4) is ____.

Answer 38

D4h

Question 39

What is the highest order of rotation in the point group C4?

Answer 39

4

Question 40

Which point group does a molecule with only a vertical mirror plane and no rotational symmetry belong to?

Answer 40

C1

Question 41

True or False: The point group Dnh has n-fold rotational symmetry and horizontal symmetry.

Answer 41

True

Question 42

Identify the point group for a molecule with a single C4 axis and four vertical planes of symmetry.

Answer 42

D4

Question 43

What is the point group of water (H2O)?

Answer 43

C2v

Question 44

Multiple Choice: Which point group does a molecule with a C2 axis and two perpendicular planes belong to? A) C2 B) D2 C) C2h D) C2v

Answer 44

B) D2

Question 45

Fill in the blank: A molecule with no symmetry operations belongs to the point group ____.

Answer 45

C1

Question 46

What is the point group of a molecule that has a center of inversion and a C2 axis?

Answer 46

D2h

Question 47

Which point group is characterized by having only rotational symmetry and no mirror planes?

Answer 47

Cn

Question 48

True or False: The point group C∞v is used to describe planar molecules.

Answer 48

False

Question 49

What is the point group of methane (CH4)?

Answer 49

T

Question 50

Identify the point group for a molecule that has both a C3 axis and three vertical mirror planes.

Answer 50

C3v

Question 51

Multiple Choice: Which point group has only one symmetry element? A) C1 B) Cs C) C2 D) D2

Answer 51

A) C1