Which of the following bonds will be most difficult to break?

(1) C-O
(2) C-P
(3) C-N
(4) C-S

Strongest Covalent Bonds: Which Bond is Hardest to Break?

What Determines Bond Strength?

The strength of a covalent bond depends on several factors, including bond energy, electronegativity differences, bond length, orbital overlap, and resonance stabilization. Bonds that are shorter and involve highly electronegative atoms tend to be stronger due to greater electrostatic attraction between the nuclei and shared electrons.

Factors Affecting Bond Strength:

1. Bond Energy: The amount of energy required to break a bond. Higher bond energy means a stronger bond. For example, the C-H bond in methane has a bond energy of ~412 kJ/mol, while the O-H bond in water has a higher energy (~463 kJ/mol), making it harder to break.
2. Electronegativity Differences: When two atoms have similar electronegativity, they share electrons more equally, forming stronger bonds. Electronegativity refers to an atom’s ability to attract shared electrons in a bond. The greater the difference in electronegativity, the more polar the bond becomes, which can sometimes weaken the bond due to increased ionic character.

For instance, the C-F bond is one of the strongest covalent bonds because fluorine is highly electronegative, resulting in a shorter bond length and strong attraction between the bonded atoms. In contrast, the C-I bond is weaker due to iodine’s lower electronegativity and larger atomic radius, leading to a longer and weaker bond. Another example is the O-H bond in water, which is stronger than an S-H bond due to oxygen’s higher electronegativity compared to sulfur, making hydrogen bonding in water more significant than in thiols.

3. Bond Length: Shorter bonds are generally stronger due to increased nuclear attraction. Triple bonds (e.g., C≡C) are stronger than double bonds (C=C), which are stronger than single bonds (C-C).
4. Orbital Overlap: The better the overlap of atomic orbitals, the stronger the bond. Sigma (σ) bonds, formed by head-on orbital overlap, are generally stronger than pi (π) bonds, which result from sideways orbital overlap.
5. Resonance and Delocalization: Bonds in resonant structures are more stable and harder to break. For example, the C-O bond in carbonate (CO₃²⁻) is stronger than a typical C-O single bond due to electron delocalization.

Understanding these factors helps predict bond strength and chemical stability in different molecules.
The strength of a covalent bond depends on several factors, including bond energy, electronegativity differences, and bond length. Shorter bonds with higher bond dissociation energy are harder to break.

Comparing the Strength of C-O, C-P, C-N, and C-S Bonds

H1: Bond Dissociation Energy and Strength

The bond dissociation energy (BDE) is the energy required to break a bond. Higher BDE indicates a stronger bond.

H2: Analysis of Given Bonds

1. C-O (Carbon-Oxygen bond) ✅
   • Bond dissociation energy: ~358 kJ/mol
   • Strong double bonds in molecules like CO₂ make it highly stable.
2. C-P (Carbon-Phosphorus bond) ❌
   • Bond dissociation energy: ~264 kJ/mol
   • Weaker than C-O due to larger atomic size of phosphorus.
3. C-N (Carbon-Nitrogen bond) ❌
   • Bond dissociation energy: ~305 kJ/mol
   • Strong, but not as strong as C-O.
4. C-S (Carbon-Sulfur bond) ❌
   • Bond dissociation energy: ~272 kJ/mol
   • Weakest among these due to the larger atomic radius of sulfur.

H3: Correct Answer

The strongest and hardest bond to break is:

(1) C-O (Carbon-Oxygen bond)

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