Question 1

For the series methane, ammonia, and water, the bond angle increases in the following order: H₂O < NH₃ < CH₄. This trend is due to ________ A) a decreasing effective nuclear charge. B) a decrease in the number of lone pairs. C) an increase in atomic radius. D) an increase in the polarity of the molecules. E) an increasing effective nuclear charge.

Accepted Answer

The bond angle increases due to a decrease in the number of lone pairs, which causes greater repulsion and reduces the bond angle in water and ammonia compared to methane.

Question 2

Which electron-pair geometry corresponds to a steric number of 2?
A) linear
B) trigonal planar
C) tetrahedral
D) trigonal bipyramidal
E) octahedral

Accepted Answer

The steric number of 2 corresponds to a geometry that has only 2 bonding pairs or lone pairs around the central atom. The only option with this geometry is linear.

Question 3

Which of the following has the largest bond angle? A) CF₄ B) NF₃ C) F₂O D) NF₂^- E) NH₃

Accepted Answer

A

Question 4

The tetrahedral bond angle is ________. A) 90^o B) 180^o C) 109^o D) 120^o E) 105^o

Accepted Answer

The tetrahedral bond angle is the angle formed between any two bonds in a tetrahedral molecule. This angle is approximately 109.5 degrees due to the geometry of the tetrahedron. Therefore, the best choice is C which represents 109^o.

Question 5

The correct H-N-H bond angle in NH₃ is ________ A) the same as the H-O-H angle in water. B) exactly 109.5$\degree$. C) greater than 109.5$\degree$. D) less than 109.5°. E) 120°.

Accepted Answer

The H-N-H bond angle in NH₃ is approximately 107°, which is less than the tetrahedral angle of 109.5° due to the presence of a lone pair on nitrogen that repels the bonding pairs, compressing the bond angle.

Question 6

Which electron-pair geometry has the lowest electron-electron repulsive forces?
A) linear
B) trigonal planar
C) tetrahedral
D) trigonal bipyramidal
E) octahedral

Accepted Answer

In a linear electron-pair geometry, the electron pairs occupy the furthest possible distance from each other, leading to the lowest electron-electron repulsive forces.

Question 7

Arrange the interactions between pairs of electrons in order of increasing strength.
A) bonding pair-bonding pair < lone pair-bonding pair < lone pair-lone pair
B) bonding pair-bonding pair < lone pair-lone pair < lone pair-bonding pair
C) lone pair-lone pair < lone pair-bonding pair < bonding pair-bonding pair
D) lone pair-lone pair < bonding pair-bonding pair < lone pair-bonding pair
E) lone pair-bonding pair < bonding pair-bonding pair < lone pair-lone pair

Accepted Answer

Lone pair-lone pair interactions are the strongest due to the high electron density and repulsion, followed by lone pair-bonding pair, and bonding pair-bonding pair interactions are the weakest.

Question 8

Which statement about VSEPR theory is not correct?
A) The molecular shape or geometry is determined by the positions of the atoms in the molecule.
B) In VSEPR theory, the shape or geometry of a molecule is determined by electron-electron repulsion.
C) The steric number of a central atom is the sum of the number of bonds around the atom.
D) The steric number has five values from 2 to 6.
E) The electron-pair geometry is determined by the positions of the bonds and lone pairs in a molecule.

Accepted Answer

The answer of Which statement about VSEPR theory is not...

Question 9

Why does the seesaw molecular geometry (ss) have a lower energy than the trigonal pyramidal molecular geometry (tp) in an AB₄ molecule with a trigonal bipyramidal electron-pair geometry? A) The ss geometry has fewer lone-pair bonding-pair interactions at 90^o. B) The ss geometry has fewer lone-pair bonding pair interactions at 120^o. C) The ss geometry has fewer bonding-pair bonding-pair interactions at 120^o. D) The ss geometry has fewer bonding-pair bonding-pair interactions at 90^o. E) The ss geometry has fewer lone-pair lone-pair interactions at 90^o.

Accepted Answer

The seesaw (ss) geometry has fewer lone-pair bonding-pair interactions at 90 degrees compared to the trigonal pyramidal geometry, which results in lower repulsion and thus lower energy for the seesaw geometry.

Question 10

Which one of the statements A-D about electron-pair geometry and molecular geometry is not correct?
A) The electron-pair geometry identifies the relative positions of the bonding regions of electrons and the lone pairs of electrons around a central atom in a molecule.
B) The molecular geometry identifies the relative positions of the atoms around a central atom in a molecule.
C) If there are no lone pairs, then the electron-pair geometry and the molecular geometry are the same.
D) The molecular geometry differs from the electron-pair geometry when the number of atoms around the central atom is smaller than the number of regions of electron density.
E) Statements A-D are all correct.

Accepted Answer

All statements A-D correctly describe aspects of electron-pair geometry and molecular geometry. Statement A defines electron-pair geometry, B defines molecular geometry, C explains the condition under which both geometries are the same, and D explains a scenario where the two geometries differ, which is accurate.

Question 11

Which statement about VSEPR theory is not correct?
A) VSEPR is an acronym for valence-shell electron-pair repulsion.
B) In VSEPR theory, the shape or geometry of a molecule is determined by electron-electron repulsion.
C) The steric number of a central atom is the sum of the number of bonds and lone pairs around the atom.
D) The steric number has five values from 2 to 6.
E) The molecular shape or geometry always is the same as the electron-pair geometry.

Accepted Answer

The molecular shape or geometry may be different from the electron-pair geometry in cases where there are lone pair-lone pair or lone pair-bond pair repulsions that distort the shape of the molecule.

Question 12

In VSEPR theory, molecular geometry is determined by ________
A) electron-proton attractive forces.
B) electron-electron attractive forces.
C) electron-electron repulsive forces.
D) proton-proton repulsive forces.
E) electron-nucleus attractive forces.

Accepted Answer

According to VSEPR theory, molecular geometry is determined by electron-electron repulsive forces. Electrons in a molecule repel each other, leading to a geometry that minimizes the repulsive forces between electron pairs. This leads to various molecular shapes such as linear, trigonal planar, tetrahedral, etc.

Question 13

Which electron-pair geometry corresponds to a steric number of 5?
A) linear
B) trigonal planar
C) tetrahedral
D) trigonal bipyramidal
E) octahedral

Accepted Answer

The steric number of 5 corresponds to the trigonal bipyramidal electron-pair geometry. This geometry has five electron pairs, three in a trigonal-planar arrangement and two perpendicular to the plane.

Question 14

Which bond angle is the smallest? A) H-C -H in CH₄ B) H-C -H in C₂H₄ C) H-C -H in H₂CO D) H-C -C in C₂H₂ E) H-C -O in H₂CO

Accepted Answer

The H-C-H bond angle in CH₄ (methane) is the smallest among the options because it has a tetrahedral geometry with bond angles of approximately 109.5°. The other molecules have different geometries or electron repulsions that lead to larger bond angles.

Question 15

A triatomic molecule with a bond angle close to 120^o could be ________. A) SO₂ B) N₂O C) HCN D) CO₂ E) BeH₂

Accepted Answer

The answer of A triatomic molecule with a bond angle...

Question 16

Which statement A-D about VSEPR theory is not correct?
A) The molecular shape or geometry can differ from the electron-pair geometry.
B) In VSEPR theory, the shape or geometry of a molecule is determined by electron-electron repulsion.
C) The steric number of a central atom is the sum of the number of bonds and lone pairs around the atom.
D) The steric number has five values from 2 to 6.
E) Statements A-D are all correct.

Accepted Answer

Statements A through D are all correct in the context of VSEPR theory. A) highlights the difference between molecular shape and electron-pair geometry, B) emphasizes the role of electron-electron repulsion in determining molecular shape, C) accurately defines the steric number, and D) is incorrect because the steric number can indeed range beyond the values of 2 to 6, accommodating various molecular geometries.

Question 17

Which electron-pair geometry corresponds to a steric number of 4?
A) linear
B) trigonal planar
C) tetrahedral
D) trigonal bipyramidal
E) octahedral

Accepted Answer

A steric number of 4 corresponds to a tetrahedral electron-pair geometry, where there are four electron pairs (either bonding or lone pairs) around the central atom.

Question 18

Which statement about the shape or geometry of a molecule is not correct?
A) Physical properties of a substance are not affected by the shape of the molecules.
B) The shape of a molecule refers to the three-dimensional arrangement of the atoms in space.
C) Solubility of a substance in a solvent is affected by the shape of the molecules.
D) Taste and aroma of a substance are affected by the shape of the molecules.
E) Biological activity and chemical reactivity of a substance are affected by the shape of the molecules.

Accepted Answer

Physical properties such as melting point, boiling point, and density are affected by the shape of molecules. For example, the melting point of a substance can be affected by the degree of symmetry in its molecules.

Question 19

Which electron-pair geometry corresponds to a steric number of 3?
A) linear
B) trigonal planar
C) tetrahedral
D) trigonal bipyramidal
E) octahedral

Accepted Answer

A steric number of 3 corresponds to three electron pairs around the central atom, which results in a trigonal planar electron-pair geometry.

Question 20

Which electron-pair geometry corresponds to a steric number of 6?
A) linear
B) trigonal planar
C) tetrahedral
D) trigonal bipyramidal
E) octahedral

Accepted Answer

The steric number of 6 corresponds to an octahedral electron-pair geometry. This is because an atom with a steric number of 6 has six regions of electron density (bonds or lone pairs) around it, leading to an octahedral shape.

Quiz 9: Molecular Geometry: Shape Determines Function

For the series methane, ammonia, and water, the bond angle increases in the following order: H2O < NH3 < CH4. This trend is due to ________

Which electron-pair geometry corresponds to a steric number of 2?

Which of the following has the largest bond angle?

The tetrahedral bond angle is ________.

The correct H-N-H bond angle in NH3 is ________

Which electron-pair geometry has the lowest electron-electron repulsive forces?

Arrange the interactions between pairs of electrons in order of increasing strength.

Which statement about VSEPR theory is not correct?

Why does the seesaw molecular geometry (ss) have a lower energy than the trigonal pyramidal molecular geometry (tp) in an AB4 molecule with a trigonal bipyramidal electron-pair geometry?

Which one of the statements A-D about electron-pair geometry and molecular geometry is not correct?

Which statement about VSEPR theory is not correct?

In VSEPR theory, molecular geometry is determined by ________

Which electron-pair geometry corresponds to a steric number of 5?

Which bond angle is the smallest?

A triatomic molecule with a bond angle close to 120o could be ________.

Which statement A-D about VSEPR theory is not correct?

Which electron-pair geometry corresponds to a steric number of 4?

Which statement about the shape or geometry of a molecule is not correct?

Which electron-pair geometry corresponds to a steric number of 3?

Which electron-pair geometry corresponds to a steric number of 6?

For the series methane, ammonia, and water, the bond angle increases in the following order: H₂O < NH₃ < CH₄. This trend is due to ________

The correct H-N-H bond angle in NH₃ is ________

Why does the seesaw molecular geometry (ss) have a lower energy than the trigonal pyramidal molecular geometry (tp) in an AB₄ molecule with a trigonal bipyramidal electron-pair geometry?

A triatomic molecule with a bond angle close to 120^o could be ________.