Bond energies main group

The third part of the EDA investigation of nonpolar bonds between main group elements in polyatomic molecules focuses on the difference between atoms that come from different rows of the periodic system. The changes in the nature of the homopolar bonds in H3E-EH3 are given in Table 13.6. The results of the EDA analyses predict that the interaction energies decrease monotonically from the lighter elements... 

Point 4 The metal-ligand bonds of transition metal complexes in high oxidation states are similar to normal covalent bonds of main group elements, which are frequently predicted with accurate interatomic distances already at the HF level of theory. The bonding of low oxidation state transition metal complexes is similar to that of donor-acceptor complexes, which need correlation energy for a reliable calculation of the bond lengths, particularly when the donor-acceptor interaction is not strong. ... 

An atom s valence electrons are those that are important in chemical bonding. For main-group elements, the valence electrons are those in the outermost principal energy level. For transition elements, we also count the outermost d electrons among the valence electrons (even though they are not in an outermost principal energy level). The chemical properties of an element depend on its valence electrons, which are instrumental in bonding because they are held most loosely (and are therefore the easiest to lose or share). We can now see why the elements in a column of the periodic table have similar chemical properties they have the same number of valence electrons. 

All the elements in a main group have in common a characteristic valence electron configuration. The electron configuration controls the valence of the element (the number of bonds that it can form) and affects its chemical and physical properties. Five atomic properties are principally responsible for the characteristic properties of each element atomic radius, ionization energy, electron affinity, electronegativity, and polarizability. All five properties are related to trends in the effective nuclear charge experienced by the valence electrons and their distance from the nucleus. 

Such secondary bonds are formed by donation from the lone pair of a nucleophile into the a orbital of a covalent bond ( n —> a attack ). Weak covalent bonds (implying low-energy a levels) are easier attacked by n - a overlap, leading to unsymmetric or symmetric 3c le bonds, than strong bonds this is why supramolecular arrays, due to secondary interactions or 3c-4e bonds, play a particular role in the chemistry of the heavier main group elements. 

The first-row homonuclear diatomic molecules A2 of main-group elements (A = B, C, N, O, F) exhibit a well-known diversity of ground-state multiplicities, bond lengths, and bond energies. Calculated potential-energy curves for low-lying singlet and triplet states of these species are pictured in Fig. 3.27 and summarized in Table 3.13 (with comparison experimental values). Because these homonuclear... 

---