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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.
Iodine can form compounds using multiple oxidation states. Iodine is quite reactive, but it is much less reactive than the other halogens. For example, while chlorine gas will halogenate carbon monoxide, nitric oxide, and sulfur dioxide (to phosgene, nitrosyl chloride, and sulfuryl chloride respectively), iodine
A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH 3 is a Lewis base, because it can donate its lone pair of electrons.
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 ...
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.
A good example is the formation of adducts between the Lewis acid borane and the oxygen atom in the Lewis bases, tetrahydrofuran (THF): BH 3 ·O(CH 2) 4 or diethyl ether: BH 3 ·O(CH 3 CH 2) 2. Many Lewis acids and Lewis bases reacting in the gas phase or in non-aqueous solvents to form adducts have been examined in the ECW model . [ 3 ]
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.