Ion, doubly-charged

If this concentration is larger than the oxygen vacancies created by thermal effects, then the conductivity from the motion of the doubly charged ions is directly proportional to the concentration of CaO (eq. 15). 

The internal structure of a liquid at a temperature near its freezing point has been discussed in Sec. 24. Each molecule vibrates in a little cage or cell, whose boundaries are provided by the adjacent molecules, as in Fig. 20, and likewise for each solute particle in solution in a solvent near its freezing point. It is clear that the question of the hydration of ions no longer arises in its original form. In aqueous solution an atomic ion will never be in contact with less than three or four water molecules, which in turn will be in contact with other water molecules, and so on. There is an electrostatic attraction, not only between the ion and the molecular dipoles in immediate contact with it, but also between the ion and molecular dipoles that are not in contact with it. For solvent dipoles that are in contact with a small doubly charged ion, such as Ca++,... 

The Electrostatic Energy. In Chapter 2 we drew attention to the fact that, when a proton transfer (117) has been carried out in a solvent, the electrostatic fields of two ions have been created and work must have been done to supply the amount of energy associated with these ionic fields. Let us now compare (117) with the process (123), both in aqueous solution at the same temperature. In both cases an (HaO)+ ion will be formed but in (123), when the proton is removed from the (IIS04)-ion, we have to separate the particles against the mutual attraction of the proton and the doubly charged ion (S04)". Consequently, more work must be done against the electrostatic forces of attraction than in the removal of a proton from a neutral particle. 

Let us consider now the work required to remove the first proton and the second proton. When the doubly charged ion of Fig. 46c has been formed, a certain amount of energy has been put into the electrostatic field of the ion this total amount differs, owing to the proximity of the two negative charges, from twice the amount put into the electrostatic... 

Two or more electro-active ions may be determined successively if their half-wave potentials differ by at least 0.4 volt for singly charged ions and 0.2 volt for doubly charged ions provided that the ions are present in approximately equal concentrations. If the concentrations differ considerably, the difference... 

As already mentioned, the experimental studies were restricted to singly charged ions. While singly charged ions are involved in the majority of the important condensed-phase ion chemistry, there are many important processes involving multiply charged ions. Thus, doubly charged ions such as Mg2+, Ca2+, Fe2+, Co2+, Ni2+, Cu2+, etc. are of paramount importance in condensed-phase chemistry and biochemistry. 

Examining Table 2, one comes to the conclusion that only Ba2+ (H20)n where n > 1 can be produced by the association reactions of M2+ with H20. For all the other ions only the monohydrate will be obtainable. For ions with high IE(M) values, even the monohydrate, M2+H20 may not be obtained because of charge transfer reactions to H20 (see equation 22). Other protic solvents will lead to charge reduction by proton transfer at different values of r. Only NH3 has been examined.71 It leads to much more facile charge reduction than H20. Many of the doubly charged ions that were observed as hydrates could not be observed as the equivalent clusters of NH3. 

The quaternary methylated diammines (CH3)3N(CH2)pN(CH3)3+ could be obtained from a methanol-water solution also for lower p values, i.e. p > 2. The greater stability of these doubly charged ions can be attributed to the more dispersed charge and to the absence of protic hydrogens. 

Doubly charged ion could not be produced from methanol-water mixture as solvent. 

Doubly charged ion could be dehydrated down to the naked ion without charge reduction. 

Difficulties of a different kind occur for proton transfer equilibria involving doubly charged ions, i.e. doubly deprotonated acids A2 or doubly protonated bases B2H +. For example, proton transfer reactions, involving the doubly protonated base B2H + and a reference base B0,... 

Figure 6.4. Fragmentation spectrum of a tryptic peptide obtained from bovine serum albumin. Peptide sequence LGEYGFQNALIVR, monoisotopic [M + H]+ = 1479.796, monoisotopic [M+2H]2+ =740.402. Upper panel full scan MS spectrum. Lower panel MS/MS spectrum of a doubly-charged ion at 740.7 m/z with a ladder of y ions, the distances between which correspond to amino acid residues (upper row of letters). A shorter series of b ions is also seen (lower row of letters). See Fig. 6.5 for description of nomenclature. Note the often observed phenomenon where multiply-charged ions lose the charge during fragmentation process and, therefore, have higher m/z values than the original parent ion.

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