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Bond strength (energy) can be directly related to the bond length / bond distance. Therefore we can use the metallic radius, ionic radius, or covalent radius of each atom in the molecule to determine the bond strength. For example, the covalent radius of boron is estimated at 83.0 pm, but the bond length of B–B in B2Cl4 is 175 pm, a significantly larger value. This would indicate that the bond between the two boron atoms is a rather weak single bond. In another example, the metallic radius of rhenium is 137.5 pm, with a Re–Re bond length of 224 pm in the compound Re2Cl8. From this data, we can conclude that the bond is a very strong bond or a quadruple bond. This method of determination is most useful for covalently bonded compounds. Determinants of ionic bond energy There are several contributing factors but usually the most important is the difference in the electronegativity of the two atoms bonding together. We should also note that the energy needed to break a particular bond, e.g., between carbon and oxygen, may also be influenced by the nature of the other atoms attached to the ones we are interested in. Thus the C=O double bond in carbon dioxide (O=C=O) has a bond energy of 187 kcal, whereas when this bond is found as part of a larger molecule, the value is closer to 170 kcal. Because of these variations, we speak of average bond energies. This table gives average bond energies for some of the bonds that are always being broken and formed in biochemical processes. Average bond energies, kcal/mole C-H 98 O-H 110 C-C 80 C-O 78 H-H 103 C-N 65 O=O 116 (2 x 58) C=O 187* (2 x 93.5) C=C 145 (2 x 72.5) (* as found in CO2) In chemistry, bond energy (E) is a measure of bond strength in a chemical bond. It is the heat required to break one Mole (unit) of molecules into their individual atoms.[1] For example, the carbon-hydrogen bond energy in methane E(C–H) is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen radicals divided by 0.5. Bond energy (E) should not be confused with bond dissociation energy ..