AP Chem unit 11

VSEPR, molecular and electron geometry

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion

What is the main idea behind VSEPR theory?

Electron groups around a central atom will be most stable when they are as far apart as possible.

What are the types of electron groups considered in VSEPR theory?

Lone pairs, single bonds, double bonds, and triple bonds.

What is the bond angle for linear electron geometry?

180 degrees

Describe the arrangement of electron groups in trigonal planar geometry.

Three electron groups occupy positions in a flat triangle around the central atom.

What is the bond angle for trigonal planar electron geometry?

120 degrees

What shape results from four electron groups around a central atom?

Tetrahedral geometry

What is the bond angle for tetrahedral electron geometry?

109.5 degrees

Describe the arrangement of electron groups in trigonal bipyramidal geometry.

Five electron groups with three in a plane and two above and below this plane.

What are the bond angles in a trigonal bipyramidal arrangement?

90 degrees (axial positions) and 120 degrees (equatorial positions)

What shape is formed with six electron groups around a central atom?

Octahedral geometry

What is the bond angle for octahedral electron geometry?

90 degrees

How do lone pairs affect molecular geometry?

Lone pairs exert greater repulsion than bonding pairs, altering the molecular shape.

What is the molecular shape when there are four electron groups and one lone pair?

Trigonal pyramidal shape

What is the molecular shape when there are four electron groups and two lone pairs?

Bent shape

What molecular shape results from five electron groups with one lone pair?

Seesaw shape

What molecular shape results from five electron groups with two lone pairs?

T-shaped

What is the molecular shape when there are six electron groups with one lone pair?

Square pyramidal geometry

What is the molecular shape when there are six electron groups with two lone pairs?

Square planar geometry

What is the first step in predicting molecular geometry?

Draw the Lewis structure.

How do you determine the number of electron groups around a central atom?

Count the bonding pairs and lone pairs.

What is the significance of molecular polarity?

Polar molecules have a difference in charge, affecting their behavior in electric fields.

How can you determine if a molecule is polar?

By assessing its geometry and the presence of a net dipole moment.

What is the molecular geometry of CO2, and is it polar or non-polar?

Linear and non-polar.

What is the molecular geometry of H2O, and is it polar or non-polar?

Bent and polar.

What does it mean if a molecule has a net dipole moment?

It indicates that the molecule has a positive and negative end, making it polar.

How does VSEPR theory help in molecular chemistry?

It allows us to account for molecular shape based on the repulsion between electron groups.

What are considered electron groups in VSEPR theory?

Lone pairs, single bonds, double bonds, and triple bonds.

What is the stability of electron groups around a central atom according to VSEPR?

Electron groups will be most stable when they are as far apart as possible.

What is the bond angle for a linear electron geometry?

180 degrees.

What is the bond angle for a trigonal planar electron geometry?

120 degrees.

What is the bond angle for a tetrahedral electron geometry?

109.5 degrees.

Describe the arrangement of electron groups in a trigonal bipyramidal geometry.

Three groups lie in a single plane, while two are positioned above and below this plane.

What are the bond angles in a trigonal bipyramidal geometry?

90 degrees for axial positions and 120 degrees for equatorial positions.

What is the bond angle for an octahedral electron geometry?

90 degrees.

What is the molecular shape when there are four electron groups and one is a lone pair?

Trigonal pyramidal shape.

What is the molecular shape when there are four electron groups and two are lone pairs?

Bent shape.

What is the molecular geometry with five electron groups and one lone pair?

Seesaw geometry.

What is the molecular geometry with five electron groups and two lone pairs?

T-shaped geometry.

What is the molecular geometry with six electron groups and one lone pair?

Square pyramidal geometry.

What is the molecular geometry with six electron groups and two lone pairs?

Square planar geometry.

How can molecular polarity be determined?

By analyzing the Lewis structure, molecular geometry, and the presence of net dipole moments.

What is a polar molecule?

A molecule that displays a difference in charge, causing a dipole moment.

What happens to the polarity of a molecule when two polar molecules are sandwiched between a nonpolar molecule?

The overall molecule becomes nonpolar, resulting in no net dipole moment.

What is the effect of lone pairs on bond angles?

Bond angles are slightly altered due to greater repulsion from lone pairs.

What is the significance of resonance in molecular geometry?

For molecules that exhibit resonance, the electron geometry remains the same regardless of the resonance form.

What is the first step in determining molecular geometry?

Draw the Lewis structure of the molecule.

How do you determine if bonds in a molecule are polar?

Evaluate the electronegativity difference between the bonded atoms.

What is the significance of summing the vectors of polar bonds?

If the vectors sum to zero, the molecule is nonpolar; if they sum to a net vector, the molecule is polar.

How do polar molecules interact with water?

Polar molecules are attracted to other polar molecules and dissolve well in water.

What is a limitation of the Lewis model?

It does not provide good numerical predictions for bond angles or structures where resonance is important.

What does Valence Bond Theory define?

It describes how chemical bonds form through the interaction of electrons and nuclei of two approaching atoms.

What results from the overlap of two half-filled orbitals?

A chemical bond forms through spin-pairing of the valence electrons.

What determines the shape of a molecule according to Valence Bond Theory?

The geometry of the overlapping orbitals.

What happens to atomic orbitals during hybridization?

Different types of orbitals mix to create a new set of degenerate orbitals.

What is the relationship between standard atomic orbitals and hybrid orbitals?

The number of standard atomic orbitals combined equals the number of hybrid orbitals formed.

What is the geometry of an atom with sp³ hybridization?

Tetrahedral geometry.

What is the purpose of hybridization in bonding?

To maximize bonding by creating new orbitals that yield the lowest overall energy for the molecule.

How does bonding occur according to Valence Bond Theory?

Bonding occurs when atomic or hybrid orbitals overlap.

What alignment is required for orbitals to interact?

Orbitals must be aligned along the axis between the atoms or be parallel and perpendicular to the interatomic axis.

What are hybrid orbitals?

Orbitals formed from the combination of standard atomic orbitals that determine the shape and energy of the molecule.

What is a characteristic of molecules with both polar and nonpolar parts?

They can exhibit complex solubility behaviors in different solvents.

What does the term 'degenerate orbitals' refer to?

Orbitals that have the same energy level after hybridization.

What is the role of resonance in molecular structures?

Resonance allows for multiple valid Lewis structures that contribute to the overall structure of the molecule.

What is the effect of molecular polarity on solubility?

Polar molecules tend to dissolve well in polar solvents, while nonpolar molecules do not.

What is the importance of bond angles in molecular geometry?

Bond angles affect the spatial arrangement of atoms and the overall shape of the molecule.