Inorganic Chemistry - A Model Chapter

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ATOMS, IONS, ENVIRON‑

MENT AND REACTIVITY

A. The element, sodium, is a metal. It reacts with many elements directly. It reacts violently with water. Air oxidizes it. Fluorine and chlorine ignite it. But sodium chloride where sodium remains as sodium ion is not reactive. In water, sodium chloride simply dissolves. Sodium chloride crystal or a solution of sodium chloride is not affected by air, chlorine or fluorine.

In order to convert sodium atom into sodium ion energy corresponding to the first ionization potential of sodium must be spent. This means that sodium ion has greater energy than sodium atom and hence sodium atom must be more stable and hence less reactive than sodium ion. Is sodium atom more stable than sodium ion? The answer is, yes. Sodium atom is definitely more stable than sodium ion. However, it is true only in vacuum. Sodium ion is a charged particle and it has no free existence. In water, sodium ion is definitely more stable than sodium atom because the sodium ions are stabilized by hydration. In a crystal of sodium chloride, sodium and chloride ions are stabilized by the lattice. A solution of CsOH in water is stabilized through entropy. And manganate ion will exist only in strongly basic solutions because in acid, neutral or slightly basic solutions, it _will readily dispropor­tionate according to the equation,

3MnO₄^2- + 4H⁺ = 2MnO₄^- + MnO₂(s) + 2H₂O

Thus, the stabilization due to factors like solvation, lattice; entropy, 'pH is called environmental stabilization.

The course of the reaction also may be affected by the medium or environment. A quintessence is Deacon Process. Oxygen will replace Chlorine from hydrogen chloride because oxygen is more electronegative than chlorine.

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1/2 O₂ + 2HCI                        Cl₂ + H₂O

In aqueous medium C1₂ will replace O₂ from water since HC1 formed has greater affinity for water.

                               Cl₂ + H₂O                       2HCl (aq)  + 1/2 O₂

B.     It is customary to state that the primary ambition of the elements like sodium is to attain eight electron configuration (octet configuration) and that is the reason why sodium loses one electron and chlorine gains one electron during the formation of sodium chloride. In fact, all atoms are electrically neutral and are fully contented with their own electrons. Hence, it may be stated that the primary requirement of any element is to attain stable electronic arrangement and hence stable charge distribution in a given environment. In fact, when metals are dissolved in molten salts of IA metals, the dissolved metals are found to remain either in the atomic state, or in the form of solvated ions of an unusually low oxidation state (A1⁴, Ca⁺, Be⁺, etc). In a plasma ⁽¹⁾ medium, it has been reported, there exists some strange substances, rarely reported in chemistry books, such as A1₂0, Ba0₃, SO, SiO, CaCl.

C.    Energy must be spent for the ionization of atoms. However, a high ionization energy may be compensated by a high lattice energy (ionization energy and lattice energy have opposite signs). This does not mean that lattice energy will always guarantee oxidation of a metal. For example, ions such as Li²⁺, Be³⁺, Na²⁺ do not exist in solution or in ionic crystals. This means that the second ionization energy of, say, sodium is so high that it will not be compensated by hydration energy or lattice energy. B³⁺ ion too has never been observed in a compound even though B³⁺ is isoelectronic with helium. The explanation offered is that the third ionization potential of boron is too high (38eV) for the production of its +3 ion. Thus, there is a limit for the number of electrons that can be removed from an atom through chemical action because there is a limit for the amount of energy released during chemical reactions. However, if the ionic valence becomes saturated even

⁽¹⁾ Plasma: Plasma is the fourth state of matter (Physicists say that there are seven states of matter). Plasma may be considered as a gas. But it is not an ordinary one. In addition to neutral atoms and molecules it contains ions and electrons. Since an ordinary gas also contains ionized particles at higher temperatures. there is no clear cut boundary line between plasma and the ordinary gas. However, when the gases begin to show high electrical conductivity or any other property of plasma, they are conventionally considered as plasma.

Major portion of the universe is made of plasma. On earth, it is prepared in an apparatus called plasmotron.

Table 5 IONIZATION ENERGIES (MJ mor1) 66

Z Element I II III 1 H 1.31 2 He 2.37 5.25 3 Li 0.52 7.29 11.81 4Be 0.89 1.75 14.84 5 B 0.80 2.42 3.65 6 C 1.08 2.35 4.62 7 N 1.40 2.85 4.57 8 0 1.31 3.38 5.30 9 F 1.68 3.37 6.05 10 He 2.08 3.95 6.12 11 Na 0.49 4.56 6.91 12 Mg 0.73 1.45 7.73 13 AI 0.57 1.81 2.74 14 Si 0.78 1.57 3.23 15 P 1.01 1.90 2.91 16 S         0.99 2.25 3.36 17 CI 1.25 2.29 3.82 18 Ar 1.52 2.66 3.9 19 K 0.41 3.05 4.4 20 Ca 0.58 1.14 4.91, 21 Sc 0.63 1.23 2.38 22 Ti 0.65 1.31 2.65 23 V 0.65 1.41 2.82 24 Cr 0,65 1.49 2.98 25 Mn 0.71 1.50 2.24 26 Fe 0.75 1.56 2.95 27 Co 0.75 1.64 3.23 28 Ni 0.73 1.75 3.39 29 Cu 0.74 1.95 3.53 30 Zn 0:90 1.73 3.83 31 Ga 0.57 1.97 2.96 32 Ge 0.76 1.53 3.30 33 As 0.94 1.79 2.73 34 Se 0.94 2.04 2.97 35 Br 1.13 2.10 3.5 36 Kr 1.35 2.35 3.56 37 Rb 0.40 2.63 3.9 38 Sr 0.54 1.06 4.21 39 Y 0.61 1.18 1.98 40 Zr 0.66 1.26 2.21 41 Nb 0.66 1.38 2.41 42 Mo 0.68 1.55 2.62 43 Tc 0.70 1.47 2.85 44 Ru 0.71 1.61 2.74 45 Rh 0.73 1.74 2.99 46 Pd 0.80 1.87 3.17 47 Ag 0.73 2.07 3.36 48 Cd 0.86 1.63 3.61 49 In 0.55 1.82 2.70 50 Sn 0.70 1.41 2.94 51 Sb 0.83 1.59 2.44

Z Element I II III 52 Te 0.86 1.79 2.69 53 I 1.00 1.84 3.2 54 Xe 1.17 2.04 3.10 55 Cs 0.37 2.23 56 Ba 0.50 0.96 57 La 0.53 1.06 1.85 58 Ce 0.52 1.04 1.94 59 Pr 0.52 1.01 2.08 60 Nd 0.53 1.03 2.11 61 Pm 0.53 1.05 2.15 62 Sm 0.54 1.06 2.26 63 Eu 0.54 1.08 2.40 64 Gd 0.59 1.17 1.99 65 Tb 0.56 1.11 2.11 66 Dy 0.57 1.12 2.20 67 Ho 0.58 1.13 2.20 68 Er 0.58 1.13 2.20 69 Tm 0.59 1.16 2.28 • 70 Yb 0.60 1.17 2.41 71 Lu 0.52 1.34 2.02 72 Hi 0.65 1.44 2.25 73 Ta 0.761 74 W 0.77 75 Re 0.76 76 Os 0,84 77 Ir 0.88 78 Pt 0.87 1.79 79 Au 0.89 1.98 80 Hg 1.00 1.80 3.30 81 TI 0.58 1.97 2.87 82 Pb 0.71 1.45 2.08 83 Bi 0.70 1.61 2.46 84 Po 0.81 85 At 86 Rn 1.03 87 Fr 88 Ra 0.50 0.97 89 Ac 0.49 1.17 90Th 0.59 1.11 1.93 91 Pa 0.57 92 U 0.59 93 Np 0.60 94 Pu 0.58 95 Am 0.57 96 Cm 0.58 97 Bk 0.60 98 Cf 0.60 99 Es 0.61 100 Fm 0.62 101 Md 0.63 102 No 0.642

Source for this book : Inorganic Chemistry by James E.Huheey.

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before the attainment of the inert gas configuration, ionicity will be, very often, overtaken by covalency. Thus, when Si is treated with excess of fluorine gas, the reaction gives SiF₄

Si (s) + 2F₂ (g)                             SiF₄ (g)

rather than giving the ionic compound, SiF₂

Si (s) + F₂ (g)                            SiF₂ (s)

As considerable amount of energy must be spent to remove electrons from neutral atoms, all simple cations must be highly electro-negative - more electro-negative than even fluorine atom. Hence, it attracts the electrons of any atom which remain in its range. Not only cations can attract electrons but also they can accommodate outside electrons. Besides, they possess both polarizing power and polarizability. These are the reasons why cations have no free existence except, however, for the brief existence inside ionization chambers. But, their potential activity towards electron donors is restricted when they are in a protective environment as in donor solvents such as water (see chapter 30).




Continued -- See the previous post