Atomic numbers group trends

By considering the trends in the vertical groups of the Periodic Table, deduce possible answers to the following questions concerning the element astatine (At), atomic number 85. 

Mercury, with interatomic distances 2-999(6) and 3-463(6), appears to have valency 3 . With bond numbers and, respectively, these distances lead to Rx = 1-410 and 1-498, the latter being much too large fort = 4(1 = 1-403), whereas bond numbers and lead to I i = 1-410 and 1-408, in approximate agreement with the value 1-418 for v — 3 . The decrease in valency from cadmium to mercury conforms to a general trend toward smaller metallic valencies with increasing atomic number in a group of elements. 

The observed dissociation enthalpies of f-Bu3Al—E(f-Pr)3 adducts (12.2 kcal/mol 9, 9.9 kcal/mol 10, 7.8 kcal/mol 11 and 6.9 kcal/mol 12) steadily decrease with increasing atomic number of the pnictine, as was expected (Fig. 3). Since steric interactions within analogously substituted adducts should become less effective with increasing atomic radius of the central group 15 element, the observed trend obviously results from the decreased Lewis basicity of the heavier pnictines. 

The electron affinity of atoms varies with atomic number. In moving across any main group blue lines), the electron affinity becomes more negative, but this is the only clear trend. 

The chemistry of the transition metals is determined in part by their atomic ionization energies. Metals of the 3d and 4d series show a gradual increase in ionization energy with atomic number (Z), whereas the trend for the 5d series is more pronounced (Figure 20-3). First ionization energies for transition metals in the 3d and 4d series are between 650 and 750 kJ/mol, somewhat higher than the values for Group 2 alkaline earth metals but lower than the typical values for nonmetals in the p block. 

These experimentally observed structural trends were confirmed by computational calculations on H3A1 and Me3Al adduct families. In each adduct family, the amount of increase of the M-X bond lengths and decrease of the X M-X bond angles (X = H, Me) compared to uncomplexed MX3 diminishes with the atomic number of the group 15 element. The structural trends very well reflect the trends observed for the thermodynamic stability of such adducts, as is illustrated in Tables XI and XII. 

Electron energy calculations now offer a coherent explanation of trends observed both across and down the periodic table and the grouping and overlaps observed in structure maps. Of particular importance are the marked changes that occur on moving to elements of higher atomic number, which means that some of the earlier assumptions concerning similarities of behaviour for compounds of the 3d, 4d, and 5d elements (Kaufman and Bernstein 1970) have had to be revised. Quantum... 

True, except for the group 18 noble gas elements, which are not assigned an electronegativity number. The trend is that electronegativity decreases with an increasing number of shells down any one atomic group (vertical column) of the periodic table. 

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