Bond weak-strong

The fluoride ion is the least polarizable anion. It is small, having a diameter of 0.136 nm, 0.045 nm smaller than the chloride ion. The isoelectronic E and ions are the only anions of comparable size to many cations. These anions are about the same size as K" and Ba " and smaller than Rb" and Cs". The small size of E allows for high coordination numbers and leads to different crystal forms and solubiUties, and higher bond energies than are evidenced by the other haUdes. Bonds between fluorine and other elements are strong whereas the fluorine—fluorine bond is much weaker, 158.8 kj/mol (37.95 kcal/mol), than the chlorine—chlorine bond which is 242.58 kJ/mol (57.98 kcal/mol). This bond weakness relative to the second-row elements is also seen ia 0-0 and N—N single bonds and results from electronic repulsion. 

Scatena, L. F., Brown, M. G. and Richmond, G. L. (2001) Water at hydrophobic surfaces weak hydrogen bonding and strong orientation effects. Science, 292, 908-912. 

The symmetry of the anions and the surface stmcture tetrahedral bisulfates bond very strongly to threefold symmetry sites of (111), but weakly to (100) and (110) surfaces. Halides adsorb more strongly on (100) surfaces. 

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. 

Bond breaking potential energy (enthalpy) of bond is increased strong bonds — weak bonds AH > 0. 

Figure 11. Crystal structure of morellic add, 15 in its 1 1 complex with pyridine. Hydrogen bonds a (strong) and b through g (weak) are marked. The pyridine molecule assists in assembling the structure.

Fig. 7 Ir isotope shift associated with weak, strong and very strong hydrogen bonds.

If the direct and reverse electron transitions (3) are in equilibrium (case when electron equilibrium at the surface is established), then a certain portion of the total number of acceptor levels A will be occupied by electrons, while a certain portion of the total number of donor levels D will be unoccupied that is, out of the total number N of the particles of a given kind chemisorbed on unit surface, a certain fraction of particles will be in a state of weak, strong acceptor, and strong donor bonding with the surface. Let us denote, respectively, by N°, N, N+ the number of particles per unit surface in each of these states and introduce the notation ... 

The effects observed for 23 (Figure 8) are particularly clear-cut, since the spectrum is fully resolved." The key to the structure of 23 lies in the prominent enhanced absorption signals of H3 (5.2 ppm) and (-0.2 ppm) and the strong emission of (2,4 ppm), H4 (2.2 ppm), and H5 (1.5 ppm). This polarization pattern supports a spepies with spin density on C3 and C6, indicating the delocalization of spin and charge into the lateral cyclopropane bond. Weakly enhanced absorption observed for H2 (5.8 ppm), (0.8 ppm), and Hi (1.75 ppm), and weak emission for H5 further support this structure type. ... 

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