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The following exergonic equilibrium gives rise to the triiodide ion: . I 2 + I − ⇌ I − 3. In this reaction, iodide is viewed as a Lewis base, and the iodine is a Lewis acid.The process is analogous to the reaction of S 8 with sodium sulfide (which forms polysulfides) except that the higher polyiodides have branched structures.
[1] [2] [3] Introduced by Gilbert N. Lewis in his 1916 article The Atom and the Molecule, a Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. [4] Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.
The aqueous solution is highly acidic, pH of 0.1N solution is 1.1. It decomposes to arsenic trioxide, elemental arsenic and iodine when heated in air at 200 °C. The decomposition, however, commences at 100 °C and occurs with the liberation of iodine.
An example of a dative covalent bond is provided by the interaction between a molecule of ammonia, a Lewis base with a lone pair of electrons on the nitrogen atom, and boron trifluoride, a Lewis acid by virtue of the boron atom having an incomplete octet of electrons. In forming the adduct, the boron atom attains an octet configuration.
The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms. [1] [2] The most common member is the triiodide ion, I −3.Other known larger polyiodides include [I 4] 2−, [I 5] −, [I 6] 2−, [I 7] −, [I 8] 2−, [I 9] −, [I 10] 2−, [I 10] 4−, [I 11] 3−, [I 12] 2−, [I 13] 3−, [I 14] 4-, [I 16] 2−, [I 22] 4−, [I 26] 3−, [I 26] 4−, [I 28] 4− and ...
Its formation explains why the solubility of iodine in water may be increased by the addition of potassium iodide solution: [11] I 2 + I − ⇌ I − 3 (K eq = ~700 at 20 °C) Many other polyiodides may be found when solutions containing iodine and iodide crystallise, such as I − 5, I − 9, I 2− 4, and I 2−
The structure of monomeric and dimeric forms have been characterized in the gas phase. [6] The monomer, AlI 3, is trigonal planar with a bond length of 2.448(6) Å, and the bridged dimer, Al 2 I 6, at 430 K is a similar to Al 2 Cl 6 and Al 2 Br 6 with Al−I bond lengths of 2.456(6) Å (terminal) and 2.670(8) Å (bridging).
Figure 2: A donor-acceptor interaction diagram illustrating construction of the triiodide anion σ natural bond orbitals from I 2 and I − fragments. In the natural bond orbital viewpoint of 3c–4e bonding, the triiodide anion is constructed from the combination of the diiodine (I 2 ) σ molecular orbitals and an iodide (I − ) lone pair.