The Nature of Transition Metal Compounds Groups 4 to

The Simple Forms in Which Main Group Biological Elements Occur in Aerated Soil, Water, Rivers, Lakes and Sea (or in Blood Plasma) 

Note Hardness is defined (see textbooks in Further reading ) as rjM = (/ - Af , where I is the ionisation potential of the state of M concerned and Ae is its electron affinity. I dominates for positive ions, but in aqueous solution must be considered relative to zjr (data from Ahrland, S., Chatt, J. and Davies, N.R. (1958). Quart. Rev., 12, 265-276 Pearson, R.G. (1963). J. Am. Chem. Soc., 85, 3533-3539). 

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