Bond Energy is also known as the average Bond Enthalpy and gives a measure of the strength of a chemical bond. The larger the bond energy the more will be the stability of the molecules.
Definition: Bond Energy is an average of the bond dissociation energy of the same type of bonds within the concerned compound.
Q1: How can we determine the strength of a bond by the radius of an atom?
Answer: Any of the radius i.e. metallic radius, ionic radius or covalent radius can be used to determine the strength of bond formed by the given atoms.
For example: Boron (B) has a covalent radius of 83 pm. It makes a B-B bond of bond length 175 pm in B2Cl4. This indicates that the B-B bond length is even higher than the radius of an atom of B. Thus, this is a weak bond. However, in the case of Rhenium (Re), the metallic radius is 137.5 pm. The Re-Re bond length in Re2Cl8 is 224 pm. This indicates that the Re-Re is a very strong quadruple bond.
Q2. What is the difference between a primary and secondary bond? Give 2 examples of each.
Answer: A Primary bond is formed by the mutual sharing or complete transfer of electrons. This type of bond is stronger than the secondary bond. For example: O2, NaCl.
A secondary bond is formed either due to permanent dipole or due to certain imbalances in the symmetrical charge distribution within the atom- creating a dipole. These dipoles induce a charge imbalance in their immediate neighbouring atoms. For example: N2, H2O.
Q3. How is the melting temperature of solids related to the bond energy?
Answer: The melting temperature is associated with the breaking of bonds of solid substances. The higher the melting temperature, the stronger the bond. The stronger the bond, the higher the bond energy. Hence, the melting temperature of solids has a direct relationship with the bond energy.
Q4. What is the enthalpy change for the given reaction?
Given the enthalpies:
Bonds
Bond Enthalpy (kJ mol -1 )