Formation of Ionic Compounds

Lewis dot representations) as a convenient bookkeeping method for keeping track of these chemically important electrons. We now introduce this method for atoms of elements in our discussion of chemical bonding we will frequendy use such formulas for atoms, molecules, and ions. 

Chemical bonding involves only the valence electrons, which are usually the electrons in the outermost occupied shells. In Lewis dot representations, only the electrons in the outermost occupied r and p orbitals are shown as dots. Table 7-1 shows Lewis dot formulas for atoms of the representative elements. All elements in a given group have the same outer-shell electron configuration. It is somewhat arbitrary on which side of the atom S)mibol we write the electron dots. We do, however, represent an electron pair as a pair of dots and an unpaired electron as a single dot. Because of the large numbers of dots, such formulas are not as useful for compounds of the transition metals, lanthanides, and actinides. 

Ionic bonding is the attraction of oppositely charged ions (cations and anions) in large 

The chemical and physical properties of an ion are quite different from those of the atom from which the ion is derived. For example, an atom of Na and an Na+ ion have extremely different chemical properties, it is important to keep track of charges and oxidation states. 

As our previous discussions of ionization energy, electronegativity, and electron affinity would suggest, ionic bonding can occur easily when elements that have low 

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Click Chemistry Interactive for the self-study module formation of ionic compounds. 

We can use Lewis dot formulas to represent the transfer of electrons in the formation of ionic compounds. For example, the formation of the ionic compound sodium fluoride, NaF, can be represented using Lewis dot formulas and valence electron conflgurations ... 

Lewis and many other chemists had recognized the shortcomings of the ionic bond. When diatomic molecules, such as or Cl, were considered, there was no reason why one atom should lose an electron and an identical atom should gain an electron. There had to be another explanation for how diatomic molecules formed. We have seen how the octet rule applies to the formation of ionic compounds by the transfer of electrons. This rule also helps explain the formation of covalent bonds when molecules (covalent compounds) form. Covalent bonds result when atoms share electrons. Using fluorine, F, as a representative halogen, we can see how the octet rule applies to the formation of the molecule. Each fluorine atom has seven valence electrons and needs one more electron to achieve the stable octet valence configuration. If two fluorines share a pair of electrons, then the stable octet configuration is achieved ... 

In the calculations of enthalpies of formation of ionic compounds, the differences from the accepted experimental values (which are very accurate) are probably due to the essential simplicity of the model, rather than having any other significance. If large discrepancies are found between experimental and calculated quantities, this probably means that the model is in error and that the compounds have a considerable covalent character. 

Clearly, U is the biggest number in the cycle and is the main driving force for the formation of ionic compounds. Nevertheless, the other factors can tip the balance one way or another. For example, AHSub is particularly large for the transition metals niobium, tantalum, molybdenum, tungsten, and rhenium, with the result that, in their lower oxidation states, they do not form simple ionic compounds such as ReCl3 but rather form compounds that contain clusters of bonded metal atoms (in this example, Re3 clusters are involved, so the formula is better written ResClg). 

In principle, we can use the Born-Haber cycle to predict whether a particular ionic compound should be thermodynamically stable, on the basis of calculated values of U, and so proceed to explain all of the chemistry of ionic solids. The relevant quantity is actually the free energy of formation, AGf, and this is calculable if an entropy cycle is set up to complement the Born-Haber enthalpy cycle. However, in practice AHf dominates the energetics of formation of ionic compounds. 

We have therefore deduced from the formula for the heat of formation of ionic compounds the important rule that the halogens replace one another in the order F2, Cl2, Br2, I2. There are ho known exceptions to this rule. Fluorine displaces chlorine, bromine and iodine from all chlorides, bromides and iodides, while chlorine and bromine displace iodine from all iodides. It is to be expected that the same substitution reactions can take place with the chal-cogens 02, S, Se and Te, and, since the heat of formation of the oxides is, as a rule, greater than that of the sulphides, the reactions of the type... 

The formation of ionic compounds depends on a balance of energies and energy input required to form ions must be compensated by the lattice energy of the compound. For ions in solution, a similar cycle could be drawn, including the solvation energy rather than the lattice energy. 

Redox reactions are not limited to single replacement reactions. They really describe a wide variety of reactions, but each shares the common theme of involving an oxidation and a reduction. An oxidation occurs when a substance loses electrons and becomes more positively charged. Earlier in the book we discussed a similar phenomenon in the formation of ionic compounds. Substances don t just lose electrons for no reason. They lose electrons because another substance takes them. When a substance acquires additional electrons and becomes more negatively charged, it is called a reduction. An oxidation cannot take place without a reduction, so these processes must occur simultaneously. These reactions describe the simultaneous oxidation and reduction of materials, which has earned them the name oxidation-reduction reactions. 

The formation of ionic compounds in the reactions of NF30 with strong Lewis acids was reported in the initial publications on the compound and studied in greater detail subsequently (47,288). Loss of a fluoride ion occurs as shown below, as in the reactions of NOF and N02F with Lewis acids. 

To write octet rule electronic structures for the formation of ionic compounds and to deduce the formulas of compounds of main group metals with nonmetals... 

With regard to the formation of ionic compounds, it is not too relevant whether the 8p or 7d shell is occupied in the neutral atom, as studied in extenso by Mann and Wdber (50). Instead, the significant question for more ionic compounds is whether in the ions, after all outer s, p and d electrons are removed, some g or f electrons will be in frontier orbitals or whether they might be easily excited to an outer electron shell so that they can be removed as well. Prince and Waber (103) showed that even in the divalent state of element 126 one g electron has changed to an / electronic state. However, the 8s electrons are not the first to be removed. Thus, the divalent ions will be expected to act as soft Lewis acids and possibly form covalent complex ions readily. Crystal or ligand fields influence the nature of the hybridization. Details such as directionality of bonds... 

Formation of ionic compounds from the elements appears to be one of the simpler overall reactions, but can also be written as a series of steps adding up to the overall reaction. The Born-Haber cycle is the process of considering the series of component reactions that can be imagined as the individual steps in compound formation. For the example of lithium fluoride, the first five reactions added together result in the sixth overall reaction. 

At the same time, interaction of the neutral base 1 with polyboranes or boron trifluoride does occur even at low temperatures (Scheme 17)179. NMR monitoring showed that while 1 with diborane or BF3 gave salts of similar type, 144 and 145, interaction between 1 and decaborane resulted in proton transfer, and reaction with pentaborane led to the formation of ionic compound X+ B9II 4, whose cationic part (X+) remained unidentified. 

Formation of Ionic Compounds 7-8 Polar and Nonpolar Covalent... 

Chapter 3 periodicity of eiectron arrangements in atoms importance of valence electrons Chapter 4 formation of ionic compounds, formation of covalent compounds... 

MiniLab 4.2 The Formation of Ionic Compounds ChemLab The Formation and Decomposition of Zinc Iodide... 

The force of attraction between two species is called a bond. It might be a strong attraction or a weak one, but it is a bond nonetheless. Most ionic compounds are composed of metals and nonmetals, and most covalent compounds are composed of only nonmetals. Let s start the discussion by looking at the formation of ionic compounds. 

The following three examples show the formation of ionic compounds by the complete transfer of one or more electrons from the metal to the nonmetal. In each case, the total number of electrons lost equals the total number gained. Note that each ion has the electronic configuration of a noble gas. As you inspect each example, notice how the number of electrons lost by the metal and gained by the nonmetal determines the formula of the ionic product. The formula of the product can be predicted from the electronic configurations of the reactants. 

The definitions of oxidation and reduction in terms of loss and gain of electrons apply to the formation of ionic compounds such as CaO and the reduction of ions by Zn. However, these definitions do not accurately characterize the formation of hydrogen chloride (HCl) and sulfur dioxide (SO2) ... 

Formation of Ionic Compounds Formation of Covalent Compounds... 

These reactions involve the formation of ionic compounds from neutral metal carbonyls in the presence of a Lewis base with a nitrogen or oxygen donor atom. The reaction of Fe3(CO)i2 with pyridine typifies... 

Writing equations for the formation of ionic compounds using Lewis symbois... 

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