CHM 2041 Chapter 10 Flashcards

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Questions and Answers

Why is molecular geometry important?

Molecular geometry is very important as it tells us about the shape of molecules and helps us account for their properties.

According to VSEPR theory, what determines the geometry of a molecule?

The number of electron groups around the central atom, including bonding groups and lone pairs.

Name the five basic electron geometries and their corresponding electron groups.

Linear (2 electron groups), Trigonal planar (3 electron groups), Tetrahedral (4 electron groups), Trigonal bipyramidal (5 electron groups), Octahedral (6 electron groups).

Explain the difference between electron geometry and molecular geometry.

Electron geometry is the arrangement of electron groups, while molecular geometry is the arrangement of atoms; they differ when a molecule contains one or more lone pairs. Signup and view all the answers

What is the electron and molecular geometry of a molecule with 4 electron groups, 3 bonding groups, and 1 lone pair?

Electron geometry: Tetrahedral; Molecular geometry: Trigonal pyramidal. Signup and view all the answers

What is the electron and molecular geometry of a molecule with 4 electron groups, 2 bonding groups, and 2 lone pairs?

Electron geometry: Tetrahedral; Molecular geometry: Bent. Signup and view all the answers

What is the electron and molecular geometry of a molecule with 5 electron groups, 4 bonding pairs, and 1 lone pair?

Electron geometry: Trigonal bipyramidal; Molecular geometry: Seesaw. Signup and view all the answers

What is the electron and molecular geometry of a molecule with 5 electron groups, 3 bonding pairs, and 2 lone pairs?

Electron geometry: Trigonal bipyramidal; Molecular geometry: T-shaped. Signup and view all the answers

What is the electron and molecular geometry of a molecule with 5 electron groups, 2 bonding pairs, and 3 lone pairs?

Electron geometry: Trigonal bipyramidal; Molecular geometry: Linear. Signup and view all the answers

What is the electron and molecular geometry of a molecule with 6 electron groups, 5 bonding pairs, and 1 lone pair?

Electron geometry: Octahedral; Molecular geometry: Square pyramidal. Signup and view all the answers

What is the electron and molecular geometry of a molecule with 6 electron groups, 4 bonding pairs, and 2 lone pairs?

Electron geometry: Octahedral; Molecular geometry: Square planar. Signup and view all the answers

How do you apply VSEPR theory to predict the shape of a molecule with more than one interior atom?

The same principles for predicting molecular geometries must be applied to each interior atom. Signup and view all the answers

How do you determine if a molecule is polar?

A molecule is polar if it has at least one polar bond and if the polar bonds do not cancel out to form a net dipole moment. Signup and view all the answers

What is a chemical bond according to valence bond theory?

A chemical bond is the interaction of half-filled atomic or hybrid orbitals. Signup and view all the answers

In valence bond theory, what determines the geometry of a molecule?

Geometry is determined using the hybridization concept. Signup and view all the answers

When is the interaction energy between two atoms negative in valence bond theory?

When a bond forms between the two atoms and the interaction energy decreases. Signup and view all the answers

What is hybridization, and why is it necessary in valence bond theory?

Hybridization is the combination of standard atomic orbitals to form new hybrid orbitals; it is necessary to explain bonding in some molecules. Signup and view all the answers

How does hybridization help lower the overall energy of a molecule?

Hybrid orbitals maximize orbital overlap and concentrate electron probability density, lowering the energy of the molecule. Signup and view all the answers

How is the number of hybrid orbitals related to the number of standard atomic orbitals that are hybridized?

The number of hybrid orbitals formed is always equal to the number of standard atomic orbitals that are hybridized. Signup and view all the answers

Describe a double bond according to valence bond theory and explain why rotation is restricted about a double bond.

A double bond consists of a sigma bond and a pi bond. Rotation is restricted because breaking the pi bond is required for rotation, unlike a single bond which allows free rotation. Signup and view all the answers

Match the following electron geometries with their corresponding hybridization scheme:

Linear = sp Trigonal planar = sp2 Tetrahedral = sp3 Trigonal bipyramidal = sp3d Octahedral = sp3d2 Signup and view all the answers

Study Notes

Importance of Molecular Geometry

Molecular geometry reveals the shape of molecules, which influences their properties.

VSEPR Theory

Geometry determined by the number of electron groups around the central atom, including both bonding groups and lone pairs.
Based on electron group repulsion, arranging in positions of least repulsion for stability.

Basic Electron Geometries

Linear: 2 electron groups, bond angle 180°
Trigonal Planar: 3 electron groups, bond angle 120°
Tetrahedral: 4 electron groups, bond angle 109.5°
Trigonal Bipyramidal: 5 electron groups, 120° equatorial, 90° axial
Octahedral: 6 electron groups, bond angle 90°

Electron vs. Molecular Geometry

Electron geometry refers to the arrangement of electron groups; molecular geometry refers to the arrangement of atoms.
Differences arise when lone pairs are present, as they exert greater repulsion than bonding pairs.

Specific Electron and Molecular Geometries

4 electron groups, 3 bonding, 1 lone pair: Tetrahedral electron geometry, Trigonal pyramidal molecular geometry.
4 electron groups, 2 bonding, 2 lone pairs: Tetrahedral electron geometry, Bent molecular geometry.
5 electron groups, 4 bonding, 1 lone pair: Trigonal bipyramidal electron geometry, Seesaw molecular geometry.
5 electron groups, 3 bonding, 2 lone pairs: Trigonal bipyramidal electron geometry, T-shaped molecular geometry.
5 electron groups, 2 bonding, 3 lone pairs: Trigonal bipyramidal electron geometry, Linear molecular geometry.
6 electron groups, 5 bonding, 1 lone pair: Octahedral electron geometry, Square pyramidal molecular geometry.
6 electron groups, 4 bonding, 2 lone pairs: Octahedral electron geometry, Square planar molecular geometry.

Applying VSEPR Theory

When multiple interior atoms exist, apply VSEPR principles to predict the geometry of each atom.

Determining Polarity

A molecule is polar with at least one polar bond.
To assess polarity, draw the molecular structure and evaluate for net dipole movement.
Polarity affects properties like solubility, surface tension, and melting/boiling points.

Chemical Bonding in Valence Bond Theory

A chemical bond arises from the interaction of half-filled atomic or hybrid orbitals.
Overlap between filled and empty orbitals may also be considered a bond.

Geometry and Hybridization

Molecular geometry is determined through hybridization, where standard atomic orbitals combine to form hybrid orbitals.
Hybridization stabilizes bonds by maximizing orbital overlap.

Energy Considerations in Hybridization

Hybrid orbitals reduce overall molecular energy by offering concentrated electron probability density in a directional lobe.
The number of hybrid orbitals equals the number of standard atomic orbitals hybridized.

Double Bonds in Valence Bond Theory

A double bond consists of a sigma bond (end-to-end overlap) and a pi bond (side-to-side overlap of p orbitals).
Rotation about double bonds is restricted due to the presence of the pi bond; single bonds can rotate freely since they lack this constraint.

Hybridization Correspondence to Electron Geometry

Linear: sp hybridization
Trigonal Planar: sp² hybridization
Tetrahedral: sp³ hybridization
Trigonal Bipyramidal: sp³d hybridization
Octahedral: sp³d² hybridization

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Explore the key concepts of molecular geometry and VSEPR theory in this quiz designed for CHM 2041. Understand how the structure of molecules influences their properties through fundamental definitions and principles. Perfect for studying or revising Chapter 10.