Chemistry VSEPR Theory Quiz

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Questions and Answers

What does the Steric Number (SN) represent?

The sum of atoms bonded to a central atom and lone pairs on that atom. (correct)

The number of double bonds present around a central atom.

The molecular weight of a compound.

The total number of valence electrons in a molecule.

Which of the following electron-pair geometries corresponds to a Steric Number of 4?

Trigonal planar

Tetrahedral (correct)

Trigonal bipyramidal

Linear

How does the presence of lone pairs affect molecular geometry compared to electron-pair geometry?

Lone pairs can change angles and overall geometry. (correct)

Lone pairs have no effect on molecular geometry.

Lone pairs only affect bond angles and not geometry.

Molecular geometry is always identical to electron-pair geometry.

What bond angle is expected for a molecule with a trigonal planar electron-pair geometry?

120 degrees Signup and view all the answers

Which of the following statements about bond angles is true when lone pairs are present?

Bond angles are typically less than theoretical angles. Signup and view all the answers

What is the electron-pair geometry for a molecule with a Steric Number of 2?

Linear Signup and view all the answers

How does the repulsion between bonding pairs compare to that of lone pairs?

Lone pairs exert greater repulsion than bonding pairs. Signup and view all the answers

If a molecule has one lone pair and three bonded pairs, what is its molecular geometry?

Trigonal pyramidal Signup and view all the answers

What does the Valence-Shell Electron Pair Repulsion Theory (VSEPR) predict?

The arrangement of valence electron pairs around a central atom that minimizes their mutual repulsion. Signup and view all the answers

What is the steric number (SN) for a linear molecular geometry?

2 Signup and view all the answers

The molecular geometry will be the same as the electron-pair geometry if there are no ______ on the central atom.

lone pairs Signup and view all the answers

In a trigonal planar geometry, what is the bond angle?

120° Signup and view all the answers

Match the steric number with the corresponding electron-pair geometry:

2 = Linear 3 = Trigonal Planar 4 = Tetrahedral 5 = Trigonal Bipyramidal 6 = Octahedral Signup and view all the answers

Repulsion between lone pairs and bonding pairs is less than repulsion between bonding pairs.

False Signup and view all the answers

Study Notes

Valence-Shell Electron Pair Repulsion (VSEPR) Theory

Predicts the arrangement of valence electron pairs around a central atom.
Minimizes mutual repulsion for lowest energy orientations.
Electron pair geometry describes the 3D arrangement of bonding and lone electron pairs around a central atom.
Molecular geometry describes the 3D arrangement of atoms in a molecule.
Electron-pair geometry equals molecular geometry only when no lone pairs are present.

Steric Number (SN) and Electron-Pair Geometry

SN is the sum of atoms bonded to the central atom plus lone pairs on the central atom.
SN determines electron-pair geometry:
- SN = 2: linear
- SN = 3: trigonal planar
- SN = 4: tetrahedral
- SN = 5: trigonal bipyramidal
- SN = 6: octahedral

Electron-Pair vs. Molecular Geometry

Molecular geometry differs from electron-pair geometry when lone pairs are present on the central atom.
Molecular geometry is based on the positions of bonded atoms only.

Bond Angles and VSEPR

Bond angle is the angle between two atoms bonded to a third.
Electron-pair geometry provides a theoretical bond angle.
Lone pairs influence bond angles due to greater repulsion:
- Lone pair-lone pair repulsion > lone pair-bonding pair repulsion > bonding pair-bonding pair repulsion.
- Lone pair repulsion > double bond repulsion > single bond repulsion.
- Two lone pairs cause greater repulsion than one.
In molecules with lone pairs, bond angles are less than theoretical angles.

Valence-Shell Electron Pair Repulsion (VSEPR) Theory

Predicts the arrangement of valence electron pairs around a central atom.
Minimizes electron repulsion to achieve lowest energy.
Electron-pair geometry describes the 3D arrangement of bonding and lone pairs around a central atom.
Molecular geometry describes the 3D arrangement of atoms in a molecule.
Electron-pair geometry equals molecular geometry when no lone pairs are present.

Steric Number (SN) and Electron-Pair Geometry

SN is the sum of atoms bonded to a central atom plus lone pairs on that atom.
SN determines electron-pair geometry:
- SN = 2: Linear
- SN = 3: Trigonal planar
- SN = 4: Tetrahedral
- SN = 5: Trigonal bipyramidal
- SN = 6: Octahedral

Differences Between Electron-Pair and Molecular Geometry

Lone pairs affect molecular geometry.
Molecular geometry differs from electron-pair geometry when lone pairs are present. It's defined by the positions of the bonded atoms.

Bond Angles and Repulsion

Bond angle: Angle between two atoms bonded to a central atom.
Electron-pair geometry provides theoretical bond angles.
Lone pairs cause deviations from theoretical angles due to increased repulsion.
Repulsion strength: lone pair > double bond > single bond.
Multiple lone pairs increase repulsion compared to a single lone pair.
Molecules with lone pairs have bond angles less than the theoretical angles.

SN = 2 (Linear)

Electron-pair geometry: Linear
Number of bonded atoms: 2
Number of lone pairs: 0
Molecular geometry: Linear
Bond angle: 180°
Example: CO₂
Hybridization: sp

SN = 3 (Trigonal Planar)

Electron-pair geometry: Trigonal planar
Number of bonded atoms: 3
Number of lone pairs: 0
Molecular geometry: Trigonal planar
Bond angle: 120°
Example: CH₂O
Hybridization: sp²
Electron-pair geometry: Trigonal planar
Number of bonded atoms: 2
Number of lone pairs: 1
Molecular geometry: Bent (angular)
Bond angle: less than 120° (due to lone pair repulsion)

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Description

Test your understanding of Valence-Shell Electron Pair Repulsion (VSEPR) theory and its applications in predicting molecular geometry. This quiz covers key concepts including steric number and the differences between electron-pair and molecular geometry.