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The Aqueous Chemistry of the Elements$
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George K. Schweitzer and Lester L. Pesterfield

Print publication date: 2010

Print ISBN-13: 9780195393354

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195393354.001.0001

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The Boron Group

The Boron Group

(p.150) 7 The Boron Group
The Aqueous Chemistry of the Elements

George K. Schweitzer

Lester L. Pesterfield

Oxford University Press

The elements which constitute the Boron Group of the Periodic Table are boron B, aluminum Al, gallium Ga, indium In, and thallium Tl. All five of the elements have atoms characterized by an outer electron structure of ns2np1 with n representing the principal quantum number. There are marked similarities in the elements, except for B whose small size and high charge density make it a non-metal. B evidences an oxidation state of III but shows no aqueous cation chemistry. The other elements all show cation chemistries involving an oxidation state of III, but the I oxidation state becomes progressively more stable until at Tl it is the predominant state. All ions in the group are colorless. Ionic sizes in pm are B+3(27), Al+3(53), Ga+3(62), In+3(80), Tl+3(89), and Tl+(150), with the B+3 value being hypothetical since B bonds only covalently. In line with the increasing sizes, the basicity of the oxides and hydroxides increases: H3BO3 or B(OH)3 is weakly acidic, M(OH)3 for Al, Ga, and In are amphoteric, and Tl(OH)3 or Tl2O3 is basic. The E° values in volts for the M(III)/M couples are as follows: H3BO3/B (−0.89), Al+3/Al (−1.68), Ga+3/Ga (−0.55), and In+3/In (−0.35). The E° value for the Tl+/Tl couple is −0.33 v. a. E–pH diagram. The E–pH diagram for 10−1.0 M B is presented in Figure 7.1. In the figure legend are equations which describe the lines which separate species. Considerably above the H3BO3/B line, the HOH≡H+/H2 line appears, which indicates that elemental B is thermodynamically unstable in HOH, but in practice B has a strong tendency to be non-reactive, vigorous treatment usually being required to oxidize it.

Keywords:   discovery, extraction, health aspects, oxides and hydroxides, redox reactions, solubilities

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