Fractional negative charge

For oxoacids having more than one OH group, we can determine values of pAj, pK2 etc. The difference (p/f —p/C , ) is nearly always between 4 and 5 the second and successive ionisations are always more difficult to accomplish than the first. It should not be difficult to see that SO4" is much more susceptible to protonation than S03(0H)" the former has four protonatable O atoms compared with only three in the latter, and each of these will be carrying a higher fractional negative charge than the O atoms in S03(0H)". 

Fig. 2). Electrical dipoles are thus created, the overall effect of which places a fractional negative charge (—5) on the chlorine atom and a fractional positive charge (+5) on the carbon atom. By analogy with the extreme case in which chlorine captures both shared electrons and forms an electrovalent ion pair [e.g., Na Cl — (Na) + ( Cl) ], such a covalent bond is said to have partial ionic character. ... 

Coordinate bonds are a special case of covalent bonds where the electrons for sharing are supplied by one atom. There is often a fractional positive charge on the donor atom and a fractional negative charge on the acceptor atom. CoBrs 3NH3 (Figure 2.2) exhibits this type of bonding and hence traditionally it is referred to as a coordination compound. 

Bromothio- and lodoselenocarbenium Salts. When the interaction between a selenium donor molecule and the linearly coordinated I-X (X=I, Br, Cl) acceptor is particularly strong, a remarkable fractional negative charge is induced on the terminal X atom, which can behave as donor towards another molecule of acceptor In the limiting case ionic [RSe-I] - -[X-I-X]"... 

An electrostatic interpretation of the hydrogen bond between water molecules. Electronegative oxygen carries a fractional negative charge, hydrogen a fractional positive charge. 

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