The bond energy values in kJ mol⁻¹ of the C-CI bond, the C-Br bond and the C-I bond are 338, 276 and 238 respectively - Leaving Cert Chemistry - Question i - 2001
Question i
The bond energy values in kJ mol⁻¹ of the C-CI bond, the C-Br bond and the C-I bond are 338, 276 and 238 respectively. Suggest a reason for this trend.
Worked Solution & Example Answer:The bond energy values in kJ mol⁻¹ of the C-CI bond, the C-Br bond and the C-I bond are 338, 276 and 238 respectively - Leaving Cert Chemistry - Question i - 2001
Step 1
Increased atomic radius
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Answer
As you move down the group in the periodic table from chlorine (Cl) to iodine (I), the atomic radius increases. This results in greater bond lengths for the C-I bond compared to the C-Br and C-Cl bonds.
Step 2
Decreased electronegativity
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Answer
The electronegativity of iodine is lower than that of chlorine and bromine, leading to a weaker bond with carbon. This decrease in electronegativity results in less overlap between the carbon and iodine orbitals.
Step 3
Decreased bond strength
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Answer
The combination of increased bond length and decreased electronegativity reduces the bond strength. Consequently, the C-I bond has the lowest bond energy of the three.
Step 4
Greater bond length
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Answer
The longer bond lengths associated with larger atoms result in weaker bonds overall, contributing to the observed trend in bond energy values.
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