Chemistry Resonance Structures and VSEPR Theory

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Questions and Answers

What does VSEPR theory primarily help predict?

The phase changes of substances

The electrical conductivity of compounds

The reactivity of molecules

The geometrical shapes of molecules (correct)

In VSEPR theory, electron pairs around a central atom are said to be repelled due to their?

Neutral charge

Positive charge

Magnetic properties

Negative charge (correct)

Which of the following categories is NOT mentioned in the classification of molecules according to VSEPR theory?

Molecules with only single bonds

Molecules with multiple central atoms (correct)

Molecules with no lone pairs

Molecules with one or more lone pairs

According to VSEPR theory, how do electron pairs adjust their spatial arrangement?

They occupy maximum distance from each other Signup and view all the answers

Which of the following is likely to affect the geometry of a molecule?

Presence of lone pairs of electrons Signup and view all the answers

What is the primary goal of arranging electron pairs according to VSEPR theory?

To maximize distances between them Signup and view all the answers

What does the term resonance refer to in the context of molecular structures?

Multiple Lewis structures that represent the same molecule. Signup and view all the answers

In molecules of the type ABn, what does a higher 'n' indicate?

Increased complexity in molecular shape Signup and view all the answers

What is the main advantage of resonance structures for a molecule?

They stabilize the molecule by lowering its overall energy. Signup and view all the answers

What might cause distortions in the geometry of a molecule according to VSEPR theory?

Lone pairs present on the central atom Signup and view all the answers

Which of the following statements about the ozone molecule (O3) is true?

Ozone has resonance structures that depict different bond arrangements. Signup and view all the answers

Which feature distinguishes resonance structures from one another?

The arrangement and type of bonds between atoms. Signup and view all the answers

How does resonance contribute to the bonding characteristics in a molecule?

It averages the bond characteristics across different structures. Signup and view all the answers

What must be true about the canonical structures of a molecule demonstrating resonance?

They represent the same atom connectivity but differ in bond types. Signup and view all the answers

In which context would resonance structures be particularly useful?

To describe a molecule with delocalized electrons. Signup and view all the answers

What visual symbol is commonly used to denote resonance between structures?

A double-headed arrow. Signup and view all the answers

What is hybridisation in the context of molecular geometry?

The intermixing of atomic orbitals to form new hybrid orbitals. Signup and view all the answers

Which statement accurately describes hybrid orbitals formed during hybridisation?

The number of hybrid orbitals equals the number of atomic orbitals that hybridised. Signup and view all the answers

What type of overlapping occurs during the formation of an sp3 hybrid orbital?

Combination of one s and three p orbitals Signup and view all the answers

Which of the following statements about pi bonds is true?

Pi bonds consist of sideways overlapping orbitals. Signup and view all the answers

Why are hybrid orbitals used in bond formation?

They are equivalent in energy and shape. Signup and view all the answers

What type of overlap occurs in p–p overlapping?

Overlap of half filled p-orbitals to create bonds. Signup and view all the answers

Which of the following statements about sp hybridisation is false?

The hybrid orbitals are not equivalent. Signup and view all the answers

In terms of the number of orbitals, how are hybrid orbitals defined?

Equal to the atomic orbitals involved in hybridisation. Signup and view all the answers

What is the molecular geometry for a molecule with the formula AB3E?

Trigonal pyramidal Signup and view all the answers

What adjustment occurs to the bond angle in AB3E due to lone pair-bond pair repulsion?

From 120° to 119.5° Signup and view all the answers

What is the bond angle for a molecule with the formula AB2E2?

105° Signup and view all the answers

Which molecular shape would occur if AB2E2 had no lone pairs?

Tetrahedral Signup and view all the answers

In terms of repulsion strength, how does lone pair-bond pair repulsion compare to bond pair-bond pair repulsion?

It is stronger than bond pair-bond pair repulsion. Signup and view all the answers

What would logically happen to the bond angles in a tetragonal structure if one lone pair is introduced?

Decreases the angle to 107°. Signup and view all the answers

What determines the shape classification of AB3E?

The amount of lone pairs present. Signup and view all the answers

What is the primary reason for the angle distortion in the molecular geometry of AB2E2?

Presence of lone pairs. Signup and view all the answers

What is the reason for the reduction in bond angle from 109.5° to 104.5°?

lp-lp repulsion is greater than lp-bp repulsion. Signup and view all the answers

In which arrangement is the lone pair (lp) considered to be more stable?

When the lp is in an equatorial position. Signup and view all the answers

What geometric shape is described for the arrangement with the lp in an equatorial position?

Distorted tetrahedron Signup and view all the answers

How many lp-bp repulsions occur when the lone pair is in an axial position?

Three Signup and view all the answers

What is the bond angle that is commonly reduced in the presence of a lone pair?

104.5° Signup and view all the answers

Which of the following statements correctly describes the relationship between lp-lp, lp-bp, and bp-bp repulsions?

lp-lp repulsion is greater than bp-bp repulsion. Signup and view all the answers

Which term describes the shape when the lp is not in the most spatially favorable position?

See-saw configuration Signup and view all the answers

Which of the following correctly indicates the spatial positioning of rp-lp repulsions?

lp-lp repulsions impact shape more significantly than bp-bp repulsions. Signup and view all the answers

Study Notes

Resonance Structures

A single Lewis structure may not adequately represent a molecule's properties.
Ozone (O3), for example, can be equally represented by two resonance structures (I and II) showing one double bond and one single bond within the molecule.
The actual structure of ozone is a hybrid of these resonance structures, often denoted as structure III.
This hybrid structure reflects the fact that all oxygen-oxygen bonds in ozone are identical and intermediate in length between a single and a double bond.
Resonance structures are represented by a double headed arrow.
Resonance structures contribute to the stabilization of a molecule, as the energy of the resonance hybrid is less than the energy of any single contributing structure.
Resonance also averages bond characteristics, distributing electron density more evenly across the molecule.

VSEPR Theory

VSEPR theory predicts the shapes of molecules based on electron pair repulsion.
Electrons pairs in the valence shell of an atom repel each other, positioning themselves to maximize distance between their electron clouds.
The arrangement of electron pairs around the central atom depends on the number of both bonding and nonbonding (lone) pairs surrounding the atom.

Hybridisation

Hybridisation explains the geometrical shapes of polyatomic molecules.
Atomic orbitals mix to form new hybrid orbitals, which are used for bonding.
Hybrid orbitals are equivalent in energy and shape.
The number of hybrid orbitals equals the number of atomic orbitals that hybridize.
sp3 hybrid orbitals are formed by mixing one 2s and three 2p atomic orbitals.

Overlapping of orbitals

s-p overlapping: Occurs between a half-filled s-orbital and a half-filled p-orbital.
p-p overlapping: Occurs between half-filled p-orbitals of two atoms.
pi (π) bond: Formed by the sideways overlapping of atomic orbitals, creating two saucer-shaped charged clouds. The orbitals are parallel and perpendicular to the internuclear axis.

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Description

This quiz covers the concepts of resonance structures and VSEPR theory in chemistry. Learn how resonance contributes to molecular stability and shapes by predicting the arrangement of atoms based on electron interactions. Perfect for students looking to deepen their understanding of molecular geometry and bonding.