Valence Bond Theory in Chemistry
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Questions and Answers

Which bond has the highest bond strength among the following options?

  • H–I
  • H–Br
  • H–Cl
  • H–F (correct)

N2 exists at room temperature, while P2 does not exist because of the weak pi bond in P2.

True (A)

What type of hybridization occurs in CH4?

sp3

The order of bond dissociation energy in halogen molecules is ___ > ___ > ___ > ___.

<p>Cl2, Br2, F2, I2</p> Signup and view all the answers

Match the following bonding characteristics with their corresponding bond types:

<p>Strong p bond = N2 Weak bonding = P2 Higher bond strength = H–F Equal bond lengths = CH4</p> Signup and view all the answers

Which statement accurately describes s and p bonds?

<p>s-bonds have a stronger extent of overlapping than p-bonds. (A)</p> Signup and view all the answers

D-d overlapping can only occur between identical d orbitals.

<p>True (A)</p> Signup and view all the answers

What type of bond is formed by overlapping px orbitals along the x-axis?

<p>p-bond</p> Signup and view all the answers

The strength of a covalent bond is directly proportional to the extent of __________.

<p>overlapping</p> Signup and view all the answers

Match the molecules to their type of overlapping:

<p>Hydrogen = p-p overlapping Hydrogen chloride = s-p overlapping Chlorine = p-p overlapping Hydrogen bromide = p-s overlapping</p> Signup and view all the answers

Flashcards

Pi (π) Bond

A type of covalent bond formed by side-by-side overlap of atomic orbitals, leading to weaker bonds compared to sigma bonds.

Sigma (σ) Bond

Type of covalent bond where the overlapping occurs along the internuclear axis, leading to stronger bonds.

Hybridization

The process where atomic orbitals overlap, forming new hybrid orbitals that are more suited for bonding.

Bond Strength and Overlapping

The strength of a covalent bond depends on the extent of overlapping between participating atomic orbitals.

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p-p Overlap

Involves electrons in p orbitals, contributing to the formation of multiple bonds, like double and triple bonds.

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Lone pair-lone pair repulsion in bond strength

The strength of a bond is determined by the repulsion between lone pairs of electrons on adjacent atoms. Higher lp-lp repulsion leads to weaker bonds.

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Directional nature of orbitals in bond strength

The strength of a bond depends directly on the overlap between the orbitals of the atoms involved. More overlap means stronger bonds.

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Why does N2 exist at room temperature, but P2 does not?

The bond strength between two atoms is stronger when the atoms are from the same period on the periodic table (e.g. N2 vs. P2).

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Need for hybridization in CH4

When using pure orbitals, overlap is not equal and bond angles in molecules like methane (CH4) are not consistent. This inconsistency is resolved by the concept of hybridization.

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What is hybridization?

Hybridization is the mixing of atomic orbitals into new hybrid orbitals. This explains the geometry and bond strength in molecules like methane.

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Study Notes

Valence Bond Theory (VBT)

  • VBT explains chemical bonding by considering the overlap of atomic orbitals.
  • p-d overlapping (π-bonding) involves the overlapping of p and d orbitals.
    • p orbitals overlap with other p orbitals, resulting in pi bonds.
    • The combinations of d orbitals used in the overlapping are listed, along with the type of bond formed
    • Different types of d orbitals overlap with p orbitals to form different pi bonds. This can lead to differing bond types across different molecules.
  • d-d overlapping (π-bonding)
    • Different combinations of d orbitals overlap with each other to form pi bonds.
    • The combinations in the table show how different d orbitals overlap to form different kinds of pi bonds (x/y, y/z, x/z).
    • Again these different bond types can lead to differening molecules.
  • Comparison between σ and π bonds.
    • σ bonds result from head-on (axial) overlap of atomic orbitals.
    • π bonds result from sideways (lateral) overlap of atomic orbitals.
    • σ bonds are stronger than π bonds.
    • σ bonds allow free rotation around the bond axis.
    • π bonds do not allow free rotation around the bond axis.
  • Factors affecting overlapping/bond strength.
    • Size of orbital: Larger orbitals overlap less effectively than smaller ones; resulting in weaker bonds.
    • Lone pair-lone pair repulsion: Repulsion between lone pairs weakens the bond.
    • Directional nature of orbitals: The orbitals' directional properties influence bond strength. The stronger the directionality, the stronger the bond.
  • Predicting bond nature based on orbital combinations.
    • Different combinations of orbitals result in different types of bonds. The tables provide examples.
  • Number of σ and π bonds in a given molecule:
    • Example provided for the molecule CH3-CH=CH-C≡CH
    • The number of σ and π bonds in a molecule depends on how many covalent bonds are present in the structure.

Hybridisation

  • Hybridisation: Mixing of atomic orbitals to form new hybrid orbitals that have different shapes. These resulting orbitals are better positioned for bonding. 
    • Important in explaining the structure of molecules like methane where it produces a tetrahedral shape with identical bond lengths
    • C atom uses hybrid orbitals with different overlaps and shapes to form bonds.
  • Need for hybridisation
  • The presence of hybridisation is necessary for certain molecular structures, such as CH4, to be explained.

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Description

This quiz explores the concepts of Valence Bond Theory (VBT), focusing on the overlapping of atomic orbitals to explain various types of chemical bonds. Participants will examine p-d and d-d overlapping, as well as the distinctions between σ and π bonds. Test your understanding of these fundamental theories in chemical bonding.

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