Signs, gaseous elements

Find A5 for the formation of CH2Cl2(g) from its gaseous elements in their standard states. Rationalize the sign of AS . 

The sum of bond enthalpies is therefore related (with change of sign) to AHf of the gaseous compound, but with an altered reference state of gaseous atoms El(g) [rather than the standard form El(std)] for each element El, ... 

However, it would be a serious error to confuse electronegativity or ionization energy with hardness . The clearest counter-example is Tl(III) which is a rather soft central atom but which must have a rather high ionization energy. There are other physical properties which accentuate the opposite inequality signs of (1) even more, for instance the electric polarizability. Table 1 contains many values for this quantity a in the unit 10-24 cm3. Gaseous atoms and positive ions have polarizabilities which can be calculated from wavefunctions (9) by evaluating the sum of matrix elements of induced dipole moment ... 

The ffth column (o-value) contains the elements of the hyperfine coupling tensors of the coupling nuclei and states the nuclei. Where possible the signs of the tensor elements are given. The unit is mT (milli-Tesla), except for gaseous radicals where Mc/s ( = MHz) is applied. In many original papers Gauss or Mc/s are used as units. 

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