Nonmetals anion formation

Shallow acceptor levels lie close to the valence band and take up electrons from it to create holes in the valence band and produce p-type semiconductors. Interstitial nonmetal atoms often generate shallow acceptor levels because anion formation involves taking up extra electrons. Acceptor levels are said to be ionized when they take electrons from the valence band, creating holes in the process. The energy of a neutral acceptor atom is different to that of an ionized acceptor. The electrons on the ionized anions are often trapped and do not contribute to the conductivity. 

Cation formation is not restricted, as normally observed, to association with metallic species. It can also occm among nonmetals and even the most typical ones such as halogens or interhalogens, which are usually more noted for halide and polyhalide anion formation. 

The formation of most ionic compounds is exothermic because of lattice energy, the energy released when metal cations and nonmetal anions coalesce to form the solid the smaller the radius of the ions and the greater their charge, the more exothermic the lattice energy. 

To predict the electron configuration of a monatomic cation, remove outermost electrons in the order np, ns, and (n — l)d fora monatomic anion, add electrons until the next noble-gas configuration has been reached. The transfer of electrons results in the formation of an octet (or duplet) of electrons in the valence shell on each of the atoms metals achieve an octet (or duplet) by electron loss and nonmetals achieve it by electron gain. 

A common feature of metal atoms is that they are generally larger in size in comparison with nonmetal atoms. A characteristic of nonmetals is that their atoms have the ability to attach electrons to themselves, leading to the formation of anions. The opposite is true for the metals and as told they alter to cationic forms when their removable electrons leave them. 

Ionic bonding involves the transfer of electrons from one atom to another. The more electronegative element gains electrons. The less electronegative element loses electrons. This results in the formation of cations and anions. Usually, an ionic bond forms between a metal and a nonmetal. The metal loses electrons to form a cation. The nonmetal gains electrons to become an anion. The attraction of the opposite charges forms an ionic solid. 

Ionic compounds consist of positive ions (cations) and negative ions (anions) hence, ionic compounds often consist of a metal and nonmetal. The electrostatic attraction between a cation and anion results in an ionic bond that results in compound formation. Binary ionic compounds form from two elements. Sodium chloride (NaCl) and sodium fluoride (NaF) are examples of binary ionic compounds. Three elements can form ternary ionic compounds. Ternary compounds result when polyatomic ions such as carbonate (C032 ), hydroxide (OH-), ammonium (NH4+), form compounds. For example, a calcium ion, Ca2+, combines with the carbonate ion to form the ternary ionic compound calcium carbonate, CaC03. Molecular compounds form discrete molecular units and often consist of a combination of two nonmetals. Compounds such as water (H20), carbon dioxide (C02), and nitric oxide (NO) represent simple binary molecular compounds. Ternary molecular compounds contain three elements. Glucose ( 12 ) is a ternary molecular compound. There are several distinct differences between ionic and molecular compounds, as summarized in Table 1.2. 

The radii of the negative ions, anions, are bigger than those of their parent neutral atoms. The addition of an electron or electrons in the formation of an anion increases the repulsive forces between the outer electrons. Therefore, the radii of anions are bigger than those of their parent nonmetal atoms. For example,... 

Formulas of Ionic Compounds As we mentioned earlier, compounds (like atoms) must be electrically neutral. The net charge on an ionic compound must be zero. When a metal gives its electrons away to form a cation, there has to be some other species, often a nonmetal, present to accept the electrons. Thus, whenever a cation is forming, there is also a concurrent formation of an anion. Chemical systems have to remain electrically neutral. 

Nonaqueous electrolyte solutions can be reduced at negative electrodes, because of an extremely low electrode potential of lithium intercalated carbon material. The reduction products have been identified with various kinds of analytical methods. Table 3 shows several products that detected by in situ or ex situ spectroscopic analyses [16-29]. Most of products are organic compounds derived from solvents used for nonaqueous electrolytes. In some cases, LiF is observed as a reduction product. It is produced from a direct reduction of anions or chemical reactions of HF on anode materials. Here, HF is sometimes present as a contaminant in nonaqueous solutions containing nonmetal fluorides. Such HF would be produced due to instability of anions. A direct reduction of anions with anode materials is a possible scheme for formation of LiF, but anode materials are usually covered with a surface film that prevents a direct contact of anode materials with nonaqueous electrolytes. Therefore, LiF formation is due to chemical reactions with HF [19]. Where does HF come from Originally, there is no HF in nonaqueous electrolyte solutions. HF can be produced by decomposition of fluorides. For example, HF can be formed in nonaqueous electrolyte solutions by decomposition of PF6 ions through the reactions with H20 [19,30]. 

The major components of seawater can also affect the rates of ionic reactions of metals and nonmetals in seawater and other natural waters (Millero, 1985, 1989, 2001). The rates of oxidation of metals can be affected by the anions (Cl, OH, SO4, HCO3 ) in aqueous solutions. For example, the formation of the ion pairs... 

We have already seen this principle operating in the formation of ions (see Table 12.2). We can summarize this behavior as follows when representative metals and nonmetals react, they transfer electrons in such a way that both the cation and the anion have noble gas electron configurations. 

This type of bonding occurs between nonmetals. Instead of a bond formed from the attraction between a cation and an anion (as with ionic bonds), we have the formation of a bond from the sharing of electrons between atoms. 

Complex-formation and redox reactions have so far been the most frequently used for the determination of both metals and nonmetals (Table 3). A variety of transition metal ions have been thus determined including such common elements as iron, copper, and calcium and rare earths as well as technetium and europium. Common nonmetals such as nitrogen anions and phosphate, bromide, and sulfur anions have also been determined this way. However, the most important applications of noncatalytic reactions in inorganic analysis are the simultaneous determinations of metal ions. As can be seen in Table 4, a wide variety of binary mixtures and some ternary and even... 

We ve already learned that there are energy changes in the formation of ions, as represented by ionization energies and electron affinities. We also know how those energy changes vary as we move through the periodic table. Those trends correlate very well with the location of metals and nonmetals in the table, and this correlation explains the observations that metals form cations and nonmetals form anions. In each case, the ions we find in compounds are those whose formation is not too costly in energy. 

FIGURE 3.2 Ihe Formation of an Ionic Compound An atom of sodium (a metal) loses an electron to an atom of chlorine (a nonmetal), creating a pair of oppositely charged ions. The sodium cation is attracted to the chloride anion and the two are held together as part of a crystalline lattice. 

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