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Questions and Answers
Which statement accurately describes the relationship between Lewis structures and molecular shape?
Which statement accurately describes the relationship between Lewis structures and molecular shape?
- Lewis structures provide a foundation for predicting molecular shape but do not directly show it. (correct)
- Lewis structures directly depict the three-dimensional shape of a molecule.
- Lewis structures are irrelevant for determining molecular shape.
- Lewis structures are only useful for simple diatomic molecules.
According to VSEPR theory, lone pairs of electrons exert the same repulsive force as bonding pairs.
According to VSEPR theory, lone pairs of electrons exert the same repulsive force as bonding pairs.
False (B)
Explain how the presence of lone pairs on the central atom affects the bond angles in a molecule, as described by VSEPR theory.
Explain how the presence of lone pairs on the central atom affects the bond angles in a molecule, as described by VSEPR theory.
Lone pairs increase repulsion, compressing bond angles.
The shape of a molecule with four electron domains around the central atom and two bonding pairs is described as ______.
The shape of a molecule with four electron domains around the central atom and two bonding pairs is described as ______.
Match each molecular geometry with the correct number of bonding pairs and lone pairs around the central atom:
Match each molecular geometry with the correct number of bonding pairs and lone pairs around the central atom:
Which of the following statements accurately describes the relationship between Valence Bond Theory and VSEPR theory?
Which of the following statements accurately describes the relationship between Valence Bond Theory and VSEPR theory?
According to valence bond theory, a sigma (σ) bond is formed by the end-to-end overlap of atomic orbitals, resulting in electron density concentrated along the internuclear axis.
According to valence bond theory, a sigma (σ) bond is formed by the end-to-end overlap of atomic orbitals, resulting in electron density concentrated along the internuclear axis.
Describe the difference between atomic orbitals and hybrid orbitals in the context of valence bond theory.
Describe the difference between atomic orbitals and hybrid orbitals in the context of valence bond theory.
In methane ($CH_4$), the carbon atom undergoes $sp^3$ hybridization, resulting in four equivalent ______ orbitals that point towards the corners of a tetrahedron.
In methane ($CH_4$), the carbon atom undergoes $sp^3$ hybridization, resulting in four equivalent ______ orbitals that point towards the corners of a tetrahedron.
What is the significance of hybridization in valence bond theory?
What is the significance of hybridization in valence bond theory?
How does VSEPR theory explain the molecular shape of $BF_3$?
How does VSEPR theory explain the molecular shape of $BF_3$?
According to valence bond theory, the carbon atom in $CO_2$ undergoes $sp^3$ hybridization to form two sigma bonds with the oxygen atoms.
According to valence bond theory, the carbon atom in $CO_2$ undergoes $sp^3$ hybridization to form two sigma bonds with the oxygen atoms.
Explain why the bond angle in water ($H_2O$) is less than the ideal tetrahedral angle of 109.5°.
Explain why the bond angle in water ($H_2O$) is less than the ideal tetrahedral angle of 109.5°.
In Valence Bond Theory, the formation of hybrid orbitals is a direct consequence of the atom attempting to minimize ______ and achieve maximum bond strength.
In Valence Bond Theory, the formation of hybrid orbitals is a direct consequence of the atom attempting to minimize ______ and achieve maximum bond strength.
Match the following molecules with their predicted molecular shapes according to VSEPR theory:
Match the following molecules with their predicted molecular shapes according to VSEPR theory:
Which factor is MOST important in determining molecular shape according to VSEPR theory?
Which factor is MOST important in determining molecular shape according to VSEPR theory?
Valence bond theory accurately predicts bond angles even in complex molecules with multiple resonance structures.
Valence bond theory accurately predicts bond angles even in complex molecules with multiple resonance structures.
Describe the relationship between the number of hybrid orbitals formed and the number of atomic orbitals mixed during hybridization.
Describe the relationship between the number of hybrid orbitals formed and the number of atomic orbitals mixed during hybridization.
According to valence bond theory, a double bond consists of one ______ bond and one $\pi$ bond.
According to valence bond theory, a double bond consists of one ______ bond and one $\pi$ bond.
What is the primary limitation of VSEPR theory in predicting molecular geometry?
What is the primary limitation of VSEPR theory in predicting molecular geometry?
Flashcards
VSEPR Theory
VSEPR Theory
A theory used to predict the 3-D shape of a molecule based on minimizing electron pair repulsions around a central atom.
Molecular Shape
Molecular Shape
The three-dimensional arrangement of atoms in a molecule.
Trigonal Planar Geometry
Trigonal Planar Geometry
A molecule with a central atom surrounded by three regions of electron density, forming a flat, triangular shape.
Tetrahedral Geometry
Tetrahedral Geometry
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Trigonal Pyramidal Shape
Trigonal Pyramidal Shape
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Bent Shape
Bent Shape
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Valence Bond Theory
Valence Bond Theory
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Hybrid Orbitals
Hybrid Orbitals
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Sigma (σ) Orbital
Sigma (σ) Orbital
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Study Notes
Molecular Shape and Lewis Structures
- Lewis structures are helpful for understanding electron arrangement in molecules.
- Lewis structures do not show the molecule's 3D shape or the types of orbitals involved in molecule formation.
Valence Shell Electron Pair Repulsion (VSEPR) Theory
- VSEPR theory predicts a molecule's 3D shape.
- Electron pairs around an atom repel each other and the shape is adopted to minimize these repulsions.
- Determining the Lewis structure is the first step in using VSEPR theory to predict a molecule's shape.
Geometries Based on Electron Pair Repulsion
- Two electron domains result in a linear geometry with a 180° angle.
- Three electron domains lead to a trigonal planar geometry with 120° angles.
- Four electron domains create a tetrahedral geometry with 109° angles.
- Five electron domains form a trigonal bipyramidal geometry with 120° and 90° angles.
- Six electron domains result in an octahedral geometry with 90° angles.
Trigonal Planar Geometry: Boron Trifluoride (BF3)
- Boron trifluoride (BF3) has a trigonal planar shape.
- The central boron atom has three sets of electrons corresponding to the shared pairs forming the B-F bonds.
- Lone pairs on the F atoms do not affect the overall molecular shape.
Methanal (Formaldehyde)
- Methanal (CH2O) also has a trigonal planar shape.
- VSEPR theory does not distinguish between single, double, or triple bonds.
- The central carbon atom has three sets of electrons: one for each C-H bond and one for the C-O bond.
Tetrahedral Geometry: Methane (CH4)
- Methane (CH4) has a tetrahedral structure.
- The Lewis structure shows four shared pairs of electrons around the central carbon atom.
Ammonia (NH3)
- Ammonia (NH3) has a tetrahedral arrangement of electron pairs but a trigonal pyramidal shape
- The central nitrogen has four sets of electrons in a tetrahedral arrangement.
- Only three of these are shared pairs, and the molecule's shape is defined by the arrangement of the bonds.
Water (H2O)
- Water (H2O) has a bent shape.
- The central oxygen has four sets of electrons with a tetrahedral arrangement.
- Two shared pairs forming O-H bonds define the shape.
Repulsion of Lone Pairs
- Lone pairs repel more than shared pairs.
- The H-C-H bond angle in CH4 is 109°, in NH3 the H-N-H angle is 107°, and in H2O, the H-O-H bond angle is 104.5°.
Valence Bond Theory and Overlap of Orbitals
- VSEPR theory helps in understanding molecular shape.
- The types of orbitals, bonding, and lone pairs of electrons also need consideration.
- Valence Bond Theory says that a bond forms by overlapping half-filled atomic orbitals to create a new orbital containing a pair of electrons.
Sigma (σ) Orbitals
- A sigma (σ) orbital is spherically symmetrical about the internuclear axis.
Bonding in Methane and Hybrid Orbitals
- Lewis structures and VSEPR theory suggest methane has a tetrahedral structure with H-C-H bonds at 109.5°.
- The electron configuration of carbon is 1s² 2s² 2p².
- Valence electrons on the carbon atom are in 2 different types of atomic orbitals.
- Four half-filled orbitals are needed, which are all the same and lie at 109° to each other.
- Mixing the wavefunctions of the 2s and 2p orbitals can achieve this to make new types of orbitals – hybrid orbitals.
- Hybrid orbitals always lead to sigma bonds.
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