Thallium ionization energy

Arrange the following atoms in order of increasing first ionization energy boron, thallium, gallium. 

Thallium and lead have higher values of their first ionization energies than expected from the trends down their respective groups, because their p-orbitals are more compact. The relativistic effect upon the 6p-orbitals of the elements from Tl to Rn is to reinforce a stabilization of one orbital with respect to the other two. Instead of the expected trend, the first ionization energies ofTl, Pb and Bi ( + 589, +715 and +703 kJ mol- ) do not show a general increase like those of In, Sn and Sb (+558, +709 and + 834 kJ mol ) the value for Bi is lower than that of Pb. 

Element 113. Detailed predictions of element 113 (eka thallium) have been given by KeUer et al. (78). In this chemical group III A the main oxidation state is 3 only T1 has also a monovalent state which is associated with the ionization of the single 6 1/2 electron and the relatively increased stability of the 6s electrons. From this behavior, the high ionization energy of the 7pi/2 electron, and the even more increased stability of the 7s electrons, the principal oxidation state of element 113 is expected to be -(-1. 

Scott and Schmit [8.78] have reported a careful study of the infrared properties of thallium-doped Si, doped as highly as 5 x 10 atoms/cm thallium acts as an acceptor. They measured an infrared ionization energy of0.246 eV, corresponding to a long-wavelength cutoff = 5.0 pm, well suited for 3-5 pm detection. They also estimated a peak optical cross section of 2.6 x 10 cm for thallium in Si. Later work by Brotherton and Gill [8.79] verified the 0.24 eV ionization energy of thallium by means of thermal emission rate measurements. 

The two electrons in the low-energy s, orbital (with j - A and with m. values of + / and -A) arerelativistically stabilized with respect to the p levels, and form the inert pair typical of the chemistry of the 6p elements. In thallium the single 6p electron is in the p j orbital and to achieve trivalency a promotion of one of the 6s electrons to the relatively higher energy pjp orbital is necessaiy. In the lead atom, the two 6s electrons occupy the s,p orbital. The Pjy orbital is doubly occupied in lead and in bismuth. The single occupation of the destabilized p, orbital in bismuth explains the observation that the first ionization energy of the element (703 kJ mol ) is lower than that of lead (715 kJ mol ). 

Thallium (Tl) is a neurotoxin and exists mostly in the T1(I) oxidation state in its compounds. Aluminum (Al). which causes anemia and dementia, is only stable in the Al(III) form. The first, second, and third ionization energies of Tl are 589, 1971, and 2878 kj/mol, respectively. The first, second, and third ionization energies of Al are 577.5, 1817, and 2745 kJ/mol, respectively. 

Using Slater s rules, calculate the effective nuclear charge acting on the 3f> valence electron of aluminum. Do a similar calculation for the valence /> electrons of gallium, indium, and thallium, respectively. Comment on the results relative to the first ionization energies of these elements. 

From boron to aluminium, there is the usual drop from the second row to the third row of the Group, but thereafter, the values remain unexpectedly high, most notably at thallium whose first ionization energy exceeds that of aluminium. In Section 8, you saw that there is a steep drop in ionization energy when a new Period begins, followed by an overall increase across a Period as the nuclear charge builds up. 

The first ionization energies of the Group II and Group III elements. There is a marked decrease between magnesium and barium, which is not matched by that between aluminium and thallium. 

Unexpectedly high ionization energies for gallium, indium and thallium make conversion of the metals into ions more difficult. They are a major contribution to the greater resistance to oxidation revealed in Table 9.3. 

In fact, the product is TL(aq) thallium, more than any other Group III metal, has a prominent +1 oxidation number. The build-up of nuclear charge in the preceding 4f and 5d block elements leaves thallium s ionization energies higher than they would otherwise be. The higher oxidation number is therefore harder to attain, and the state most stable to oxidation or reduction is +1. 

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