Below is a table of average bond lengths. The hydrogen-halide bond lengths increase as we go down a group on the periodic table. For example, H-Cl has a bond length of 127 pm and H-Br has a bond length of 142 pm. This is because as we go down the group, the atomic radius increases.
As we go across a period we see bond length decreases. If we look at CH4, NH3, H2O, and HF, we see the H-F bond is shorter while the C-H bond is longest.
Multiple bonds, double and triple bonds are shorter than single bonds. For example, C-C is 154 pm, C=C is 134 pm, and C≡C is 120 pm. The C≡C bond is the shortest.
The longer a bond, the weaker its bond strength. The shorter the bond, the stronger the bond strength. The table below lists bond strengths for different bonds. For the hydrogen halides, the bond strength decreases as we go down Group 7A in the periodic table.
*Bond dissociation energies for diatomic molecules can be directly measured. The rest are average bond energies.
The bond strength increases as we go across a period, and decreases as we go down a group as seen in the figure below. Multiple bonds have higher bond dissociation energies than single bonds.
The longer the bond length, the weaker the bond, and the shorter the bond length, the stronger the bond. It will take more energy to break a shorter or a multiple bond than it would to break a longer bond. In a multiple bond, there are more electrons shared, therefore, the bond is stronger than the corresponding single bond.
Worksheet: Bond Length, Bond Strength, and Electronegativity
Exercises
Exercise 1. Using only the periodic table, order the following from shortest to longest bond length. C-Cl, C-P, and C-S.
Exercise 2. Using only the periodic table, order the following from lowest to highest bond strength. C-Cl, C-P, C-S.
Exercise 3. Which of the following molecules have the strongest carbon-carbon bond?
CH3CH=CHCH3, C3H8, HC≡H, H2C=O.
Exercise 4. Which of the following bonds is more easily broken?
H-N, N-N, N=N, N≡N
Exercise 5. Which bond would have the highest bond dissociation energy?
H3C-CH3, HC≡CH, H2C=CH2, Cl2C=CCl2
Check Solutions/Answers to Exercises
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