College Chemistry : Molecular Geometries and VSEPR Theory

Study concepts, example questions & explanations for College Chemistry

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Example Questions

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Example Question #1 : Molecular Geometries And Vsepr Theory

What is the molecular geometry of ?

Possible Answers:

T-shaped

Seesaw

Trigonal pyramidal

Square planar

Correct answer:

Seesaw

Explanation:

Start by drawing the Lewis structure of .

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Selenium has  fluoride molecules bonded to it, and it has a lone pair. This means its steric number is . A molecule with a steric number of  and  lone pair has a seesaw molecular geometry. Note that this is an expanded octet.

Example Question #23 : Introductory Topics

What is the molecular geometry of ?

Possible Answers:

Trigonal planar

T-shaped

Linear

Bent

Correct answer:

Bent

Explanation:

Start by drawing the Lewis structure of .

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Notice that the central oxygen atom has  other oxygen atoms bonded to it, as well as a lone pair. This means it has a steric number of . A molecule with a steric number of  and  lone pair has a bent molecular geometry.

Example Question #3 : Molecular Geometries And Vsepr Theory

What is the molecular geometry of the bonds surrounding the circled atom?

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Possible Answers:

Linear

Bent

T-shaped

Tetrahedral

Correct answer:

Bent

Explanation:

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Start by determining the steric number of the circled oxygen atom. Since it is bonded to a hydrogen and a carbon and has  lone pairs, its steric number must be . A molecule with a steric number of  and  lone pairs has a bent molecular geometry.

Example Question #4 : Molecular Geometries And Vsepr Theory

What is the molecular geometry of the circled element?

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Possible Answers:

Trigonal pyramidal

Tetrahedral

Trigonal planar

T-shaped

Correct answer:

Trigonal planar

Explanation:

In order to figure out the molecular geometry of the circled element, first determine the steric number.

The circled nitrogen has three electron groups attached to it, so its steric number is . Since there are no lone pairs on the nitrogen, its electron geometry and its molecular geometry are both trigonal planar.

Example Question #1 : Molecular Geometries And Vsepr Theory

What is the molecular geometry of the circled element?

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Possible Answers:

T-shaped

Linear

Tetrahedral

Bent

Correct answer:

Bent

Explanation:

In order to figure out the molecular geometry of the circled element, first determine the steric number.

Since the circled oxygen has four electron groups attached to it, its steric number is . The circled oxygen also has  lone pairs of electrons attached to it; therefore, it has a bent molecular geometry.

Example Question #6 : Molecular Geometries And Vsepr Theory

Which of the following correctly describes the VSEPR shape of the water molecule, ?

Possible Answers:

Bent

None of these

Trigonal planar

Trigonal bipyramidal 

Linear

Correct answer:

Bent

Explanation:

In the water molecule, there are four electron groups (steric number is four). Two of them (two pairs) are bonded (the bonds between both hydrogen atoms and the oxygen atom), while the other two are lone pairs on oxygen. Thus, the water molecule has a bent shape, with two bonded electron groups and two lone pair electron groups. A linear VSEPR shape has two electron groups, a trigonal planar has three electron groups, and a trigonal bipyramidal shape has five electron groups.

Example Question #25 : Introductory Topics

Which of the following is true of Valence Bond theory and Molecular Orbital theory?

Possible Answers:

The Valence Bond theory is the mathematical combination of atomic orbitals to produce anti bonding and bonding orbitals while the Molecular Orbital theory states that covalent bonds are formed from atomic orbital overlap. 

Neither Valence Bond theory nor Molecular Orbital theory produces hybridized geometries. 

The Valence Bond Theory states that covalent bonds are the result of electron repulsion while the Molecular Orbital theory states that covalent bonds form as a result of atomic overlap.  

The Valence Bond theory states that covalent bonds are formed from atomic orbital overlap while the Molecular Orbital theory is the mathematical combination of atomic orbitals to produce anti bonding and bonding orbitals.  

Both Valence Bond theory and Molecular Orbital theory produce hybridized geometries through anti bonding and bonding orbitals. 

Correct answer:

The Valence Bond theory states that covalent bonds are formed from atomic orbital overlap while the Molecular Orbital theory is the mathematical combination of atomic orbitals to produce anti bonding and bonding orbitals.  

Explanation:

The Valence Bond theory states that covalent bonds are formed from atomic orbital overlap while the Molecular Orbital theory is the mathematical combination of atomic orbitals to produce anti bonding and bonding orbitals.  

Hybridization occurs through combining atomic orbitals, a concept consistent with Valence Bond theory. Common bonds found in Valence Bond hybridization are sigma and pi bonds which overlap end-to-end or side-to-side respectively. Orbitals are combined in Molecular Orbital theory, producing either bonding or anti bonding orbitals. Molecular Orbital theory shows the destructive or constructive interference of sigma and pi bonds (displayed through bonding and anti bonding orbitals).  

Example Question #26 : Introductory Topics

A molecule has 4 electron groups and 2 lone pairs. What is the VSEPR notation, electron group geometry, and molecular geometry?

Possible Answers:

, octahedral, square planar 

, octahedral, square pyramidal 

, tetrahedral, bent 

, trigonal bipyramidal, t-shaped

, tetrahedral, tetrahedral 

Correct answer:

, tetrahedral, bent 

Explanation:

A molecule that has 4 electron groups and 2 lone pairs has an VSEPR notation of:.  The  indicates the central atom, the  the number of bonding atoms, and  the number of lone pairs.  There are 2 bonding atoms and 2 lone pairs, totaling a total of 4 electron groups.  All tetrahedral geometries consist of 4 electron groups. Molecular geometries of electron groups with the tetrahedral are tetrahedral (), trigonal pyramidal (), and bent ().  

Therefore the correct answer is: , tetrahedral, bent.

Example Question #2 : Molecular Geometries And Vsepr Theory

What is the molecular geometry of the molecule ?

Possible Answers:

Trigonal bipyramidal 

Square pyramidal 

T-shaped 

Trigonal pyramidal 

Trigonal planar 

Correct answer:

T-shaped 

Explanation:

 is t-shaped. By drawing the Lewis diagram for , we see that there are 5 electron groups and 2 lone pairs on the central atom, . Electron group geometry states that molecules with 5 electron groups have a trigonal bipyramidal geometry. The molecular geometries of trigonal bipyramidal molecules can be trigonal bipyramidal (no lone pairs), seesaw (1 lone pair), t-shaped (2 lone pairs). and linear (3 lone pairs).  

 consists of 5 electron groups and 2 lone pairs and therefore fits the molecular geometry of a t-shaped molecule.  

Example Question #3 : Molecular Geometries And Vsepr Theory

Which of the following is true of both molecular orbitals and atomic orbitals?

Possible Answers:

No comparison between molecular orbitals and atomic orbitals can be made as they are consistent with different theories of bonding.  

The number of molecular orbitals are half the number of atomic orbitals for a given molecule.

The number of molecular orbitals is equal to the number of atomic orbitals for a given molecule.  

The number of atomic orbitals are twice the number of molecular orbitals for a given molecule.  

Molecular orbitals are to valence bond theory as atomic orbitals are to atomic orbital theory.  

Correct answer:

The number of molecular orbitals is equal to the number of atomic orbitals for a given molecule.  

Explanation:

The number of molecular orbitals is equal to the number of atomic orbitals for a given molecule. The number of orbitals is consistent. Molecular orbitals shows destructive and constructive interference between sigma and pi bonds. In molecular orbital diagrams, these results appear as either bonding or anti bonding energies. Atomic orbitals combine the valence shells of overlapping orbitals to form more stable electron configurations.  

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