Polyatomic anions

Polyatomic Cations. Polyatomic cations derived by addition of more protons than required to give a neutral unit to polyatomic anions are named by adding the ending -onium to the root of the name of the anion element for example, PH4, phosphonium ion HjU, iodonium ion H3O+, oxonium ion CH3OHJ, methyl oxonium ion. 

See Secs. 3.1.2.2 and 3.1.2.8 for naming monatomic and certain polyatomic anions. When an organic group occurs in an inorganic compound, organic nomenclature (q.v.) is followed to name the organic part. 

Protonated Anions. Ions such as HSOy are recommended to be named hydrogensulfate with the two words written as one following the usual practice for polyatomic anions. However, in the Nomenclature of Organic Chemistry, 1979 edition, hydrogen is used as a separate word this practice is followed in this Handbook. 

Other Polyatomic Anions. Names for other polyatomic anions consist of the root name of the central atom with the ending -ate and followed by the valence of the central atom expressed by its oxidation number. Atoms and groups attached to the central atom are treated as ligands in a complex. 

Pu(IV) forms polyatomic complexes with inorganic and organic ligands. As the number of anionic ligands increases, cationic, neutral, and anionic complexes form and the sequential stabiUty constants, typically decrease. For the following reaction, where M is Pu + and L is a ligand,... 

Nearly all cations are monatomic the majority of anions are polyatomic. 

Count the number of valence electrons. For a molecule, simply sum up the valence electrons of the atoms present. For a polyatomic anion, one electron is added for each unit of negative charge. For a polyatomic cation, a number of electrons equal to the positive charge must be subtracted. 

Polyatomic zintl anions of the post-transition elements. J. D. Corbett, Chem. Rev., 1985, 85, 383 (117). 

For other polyatomic anions, find the name of the ion in Table D.l or Appendix 3A. If hydrogen is present, add hydrogen" to the name of the anion. If two hydrogen atoms are present, add dihydrogen to the name of the anion. 

Carbon is the only Group 14/IV element that forms both monatomic and polyatomic anions. There are three classes of carbides saline carbides (saltlike carbides), covalent carbides, and interstitial carbides. The heavier elements in Group 14/IV form polyatomic anions, such as Si44 and Sn52, in which the atoms form a tetrahedron and trigonal bipyramid, respectively. 

The azide ion is a highly reactive polyatomic anion of nitrogen, N3 . Its most common salt, sodium azide, NaN3, is prepared from dinitrogen oxide and molten sodium amide ... 

In this equation, r) the absolute hardness, is one-half the difference between /, the ionization potential, and A, the electron affinity. The softness, a, is the reciprocal of T]. Values of t) for some molecules and ions are given in Table 8.4. Note that the proton, which is involved in all Brdnsted acid-base reactions, is the hardest acid listed, with t — c (it has no ionization potential). The above equation cannot be applied to anions, because electron affinities cannot be measured for them. Instead, the assumption is made that t) for an anion X is the same as that for the radical Other methods are also needed to apply the treatment to polyatomic... 

There are many different polyatomic anions, including several that are abundant in nature. Each is a stable chemical species that maintains its stmcture in the solid state and in aqueous solution. Polyatomic anions are treated as distinct units when writing chemical formulas, naming compounds, or drawing molecular pictures. The names, formulas, and charges of the more common polyatomic anions are listed in Table 3-4. You should memorize the common polyatomic ions because they appear regularly throughout this textbook. 

Most polyatomic anions contain a central atom surrounded by one to four oxygen atoms. These species are called oxoanions, and they are named according to the following guidelines ... 

CaCl2 Ammonium is not present, but there is a metal (Ca). There is no polyatomic anion, but Ca is from Group 2, and there is a halide (Cl), so this compound is ionic. 

Magnesium nitrate contains (Group 2) and the polyatomic anion NO3 . Again, there must be... 

NH4HSO4 The polyatomic ammonium cation is combined with a hydrogen-containing anion ammonium hydrogen sulfate. 

When a salt containing polyatomic ions dissolves In water, the cations separate from the anions, but each polyatomic ion remains intact. An example Is ammonium nitrate, composed of NH4 polyatomic cations and NO3 polyatomic anions. Ammonium nitrate dissolves In water to give a solution containing NH4 cations and NO3 anions, as Figure 3-21 Illustrates. 

Although the nonmetals do not readily form cations, many of them combine with oxygen to form polyatomic oxoanions. These anions have various stoichiometries, but there are some common patterns. Two second-row elements form oxoanions with three oxygen atoms carbon (four valence electrons) forms carbonate, C03, and nitrogen (five valence electrons) forms nitrate, NO3. In the third row, the most stable oxoanions contain four oxygen atoms Si04 -, P04 -, S04, and CI04. ... 

Closely related to silica are the silicate minerals, all of which contain polyatomic anions made of silicon and oxygen. The simplest silicates, called orthosilicates, contain Si04 anions. The 8104 anion is tetrahedral, with a central silicon atom bonded to four outer oxygen atoms. 

C09-0108. Carbon, nitrogen, and oxygen form two different polyatomic ions cyanate ion, NCO, and isocyanate ion, CNO". Write Lewis stmctures for each anion, including near-equivalent resonance structures and indicating formal charges. 

---