Binary ionic compound formation

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. 

We have already seen that when metals and nonmetals react to form solid binary ionic compounds, electrons are transferred and the resulting ions typically have noble gas electron configurations. An example is the formation of KBr, where the K ion has the [Ar] electron configuration and the Br- ion has the [Kr] electron configuration. In writing Lewis structures, the rule is that... 

Oxidation, Reduction, and the Formation of Binary Ionic Compounds... 

As we saw in Chapter 3, this transfer of electrons from metal atoms to nonmetal atoms is the general process for the formation of any binary ionic compound from its elements. For example, when sodium chloride is formed from the reaction of metallic sodium with gaseous chlorine, each sodium atom loses an electron, and each chlorine atom gains one. 

Depict the formation of binary ionic compounds with electron configurations, partial orbital diagrams, and Lewis electron-dot symbols ( 9.2) (SP 9.1) (EPs 9.16-9.19)... 

In stable chemical compounds, the atoms tend to achieve a noble gas electron configuration. In the formation of a binary ionic compound involving representative elements, the valence-electron configuration of the nonmetal is completed it achieves the configuration of the next noble gas. The valence or-... 

Use the octet rule to correctly predict the ions formed during the formation of ionic compounds, and write correct formulas for binary ionic compounds containing a representative metal and a representative nonmetal. (Section 4.3)... 

Figure 7.15 (a) Enthalpy of formation of ternary oxides and nitrides from their binary constituent compounds as a function of the ratio of ionic potential [16]. Reprinted with permission from [16] Copyright (1997) American Chemical Society, (b) Gibbs energy of the oxide-sulfide equilibrium for group 1 and 2 metals at 1773 K as a function of the optical basicity of the metal. 

Around 1928, Zintl had begun to investigate binary intermetallic compounds, in which one component is a rather electropositive element, e.g., an alkali- or an alkaline earth metal [1,2]. Zintl discovered that in cases for which the Hume-Rothery rules for metals do not hold, significant volume contractions are observed on compound formation, which can be traced back to contractions of the electropositive atoms [2]. He explained this by an electron transfer from the electropositive to the electronegative atoms. For example, the structure of NaTl [3] can easily be understood using the ionic formulation Na Tl" where the poly- or Zintl anion [TF] forms a diamond-like partial structure - one of the preferred structures, for a four electron species [1,2], Zintl has defined a class of compounds, which, in the beginning, was a somewhat curious link between well-known valence compounds and somehow odd intermetallic phases. 

The atomic and ionic properties of an element, particularly IE, ionic radius and electronegativity, underly its chemical behaviour and determine the types of compound it can form. The simplest type of compound an element can form is a binary compound, one in which it is combined with only one other element. The transition elements form binary compounds with a wide variety of non-metals, and the stoichiometries of these compounds will depend upon the thermodynamics of the compound-forming process. Binary oxides, fluorides and chlorides of the transition elements reveal the oxidation states available to them and, to some extent, reflect trends in IE values. However, the lEs of the transition elements are by no means the only contributors to the thermodynamics of compound formation. Other factors such as lattice enthalpy and the extent of covalency in bonding are important. In this chapter some examples of binary transition element compounds will be used to reveal the factors which determine the stoichiometry of compounds. 

The therniodynaniies of binary compound formation reflect the atomic and ionic properties of the metal and may be used to predict the slablility or otherwise of simple compounds. 

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