Monatomic negative ions

Electronic configurations of ions are obtained in much the same way as those of elements. The fluorine atom has nine electrons, so the F ion (with ten electrons) would have the same configuration as Ne gas. Similarly, the sulfide ion (S2 ) would have the argon structure. All monatomic negative ions in ordinary systems have rare gas configurations (except for a negative ion of rhenium which has been reported). 

Figure 9.3 shows the relationship between ionic radius and proton affinity in a graphical way for monatomic ions having a — 1 charge. It is clear that to a good approximation there is a correlation between the size of the anion and its proton affinity. While this is in no way a detailed study, it is clear that the smaller (and thus harder] the negative ion (with the same type of structure) the more strongly it binds a proton. 

The anion (negative ion) is named and written last. Monatomic anions are formed from nonmetallic elements and are named by replacing the end of the element s name with the suffix -ide. 

The present paper reviews and assesses the current information about the formation and identification of X , AZ , and other doubly-charged negative ion species that have been reported. It also presents mechanisms and explanations for the production of the monatomic, diatomic and polyatomic doubly-charged negative ions that have been observed. Finally, some potentially fruitful paths for the further study of these ions are indicated. 

Ar . Long-lived metastable states of negative ions of the noble gas atoms other than He are unknown to the present, although Bethge indicated he has extracted very low intensity Xe ion beams from his dense plasma Penning source. Since so little other information is available at this time, it is not inappropriate to adopt He as a model for the isoelectronic monatomic ions of Group VII and for other species. 

The discovery of doubly-charged negative ions was first reported in 1966 by Stuckey and Kiser The species observed were the monatomic 0, F, Cl , and Br , and the diatomic CN ions. Their studies also included an estimate of the lifetime of these species based on the ion flight times and a discussion of the electronic configurations and possible modes of formation of the observed ions. 

The excited states of doubly-charged negative ions larger than monatomic are also of importance in providing for long lifetimes of these species. Studies of the energy stabilities of di-, tri-, and poly-atomic l ions involve molecular orbital treatments, however, rather than the approaches just discussed for atomic l species. A variety of semiempirical molecular calculation methods are possible. 

Certainly detailed theoretical treatments of the stabilities, energetics, and electronic states of the doubly-charged negative ions, both monatomic and polyatomic, are now warranted. It was noted eariier that the EHT calculations employed here are only a zerot/i order approximation the results obtained, however, now justify an effort to employ more sophisticated approaches. The MINDO and LCAO-MO-SCF calculations mentioned above are a distinct improvement over the EHT calculations. Other calculational techniques should be brought to bear on an improved understanding of doubly-charged negative ions. 

A summary of the negative oxidation states of the s- and p-block elements, as they exist in monatomic ions, is given in Table 5.3. Examples of negative ions containing more than one s- or p-block element exist e.g. 0 - , the peroxide ion), but are not detailed in this text. 

Ionic compounds form when a metal transfers electrons to a nonmetal, and the resulting positive and negative ions attract each other to form a three-dimensional array. In many cases, metal atoms lose and nonmetal atoms gain enough electrons to attain the same number of electrons as in atoms of the nearest noble gas. Covalent compounds form when elements, usually nonmetals, share electrons. Each covalent bond is an electron pair mutually attracted by two atomic nuclei. Monatomic ions are derived from single atoms. Polyatomic ions consist of two or more covalently bonded atoms that have a net positive or negative charge due to a deficit or excess of electrons. 

Ionic compounds contain positive ions (usually a metal) and negative ions (nonmetals or polyatomic ions). The positive ion is named first and is the element name presented unchanged. The negative ion is named second. If it is a monatomic element, the element name ending is changed to —ide. Sodium chloride is a good example. The numbers of ions in the formula are not stated in the formula name. 

Ionic compounds are composed of positive ions and negative ions. The cation is always named first, and then the negative ion. Naming of the positive ion depends on whether the positive ion is monatomic. If not, special Stock names are used. If the positive ion is monatomic, the name depends on whether the element forms more than one positive ion. 

If the anion is monatomic (has one atom), the name of the element is changed by changing the ending to 4de. This ending is used for binary metal-non-metal compounds. All monatomic ions have names ending in -ide, for example, chloride, Cl , oxide, and nitride,. However, there are a few negative ions that consist of more than atom which also end in -ide, for example cyanide, CN , and hydroxide, OH. ... 

Sen, K. D., and P. Politzer. 1989. Characteristic Features of the Electrostatic Potentials of Singly-Negative Monatomic Ions. J. Chem. Phys. 90, 4370. 

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