Bond energy

Bond energy (BE) is the average of all bond-dissociation energies of a single type of bond in a given molecule. The bond-dissociation energies of several different bonds of the same type can vary even within a single molecule. For example, a water molecule is composed of two O–H bonds bonded as H–O–H. The bond energy for H2O is the average energy required to break each of the two O–H bonds in sequence: : Although the two bonds are the equivalent in the original symmetric molecule, the bond-dissociation energy of an oxygen–hydrogen bond varies slightly depending on whether or not there is another hydrogen atom bonded to the oxygen atom. Thus, the bond energy of a molecule of water is 461.5 kJ/mol (110.3 kcal/mol). When the bond is broken, the bonding electron pair will split equally to the products. This process is called homolytic bond cleavage (homolytic cleavage; homolysis) and results in the formation of radicals. ==Predicting the bond strength by radius==

The strength of a bond can be estimated by comparing the atomic radii of the atoms that form the bond to the length of bond itself. For example, the atomic radius of boron is estimated at 85 pm, while the length of the B–B bond in Diboron tetrachloride, B2Cl4 is 175 pm. Dividing the length of this bond by the sum of each boron atom's radius gives a ratio of \frac{175 \ \text{pm}}{85 \ \text{pm} + 85 \ \text{pm}} = \frac{175 \ \text{pm}}{170 \ \text{pm}} \approx 1.03 . This ratio is slightly larger than 1, indicating that the bond itself is slightly longer than the expected minimum overlap between the two boron atoms' valence electron clouds. Thus, we can conclude that this bond is a rather weak single bond. In another example, the atomic radius of rhenium is 135 pm, This method of determination is most useful for covalently bonded compounds. ==Factors affecting ionic bond energy==

In ionic compounds, the electronegativity of the two atoms bonding together has a major effect on their bond energy. The extent of this effect is described by the compound's lattice energy, where a more negative lattice energy corresponds to a stronger force of attraction between the ions. Generally, greater differences in electronegativity correspond to stronger ionic bonds. For example, the compound sodium chloride (NaCl) has a lattice energy of −786 kJ/mol with an electronegativity difference of 2.23 between sodium and chlorine. Meanwhile, the compound sodium iodide (NaI) has a lower lattice energy of −704 kJ/mol with a similarly lower electronegativity difference of 1.73 between sodium and iodine. ==See also==