Chart for part B 19) From \"A Modern Approach to Acid-Base Chemistry\" by Russ D
ID: 517997 • Letter: C
Question
Chart for part B 19) From "A Modern Approach to Acid-Base Chemistry" by Russ Drago: a) In a half page (typed) or more, explain Drago's attempts to quantify HSAB chemistry. b) Calculate enthalpy of adduct formation using Drago's E and C equation U-AH (E AE B CACB] for the following: (use the table on the next page) i) 12 and Dimethylamine ii) Trimethyl gallium and Diethylsulfide c) What does it mean that the enthalpy of adduct formation in part b i is lower than the enthalpy of adduct formation from part biiExplanation / Answer
answer A;
Drago attempt to quantify the HSAB chemistry are, An attempt is made to explain the e.c formulation for ionic interactions in terms of the ionic approximation to chemical bonding. Dravo's E-C equation is seen to be a first approximation to the bond energy equation as it is given by the ionic bonding approach.
The meaning of the ratio C/E is discussed and its relation with the hardness and softness of interacting species, as these occur in Pearson's HSAB rule, shows that the electron affinity or electronegativity of elements completely determines the chemical behavior of ionic species. This analysis illustrates the consistency of the ionic approximation to chemical bonding.The ionic approximation to chemical bonding 5 a offers the possibility of discussing the E-C equation more in detail. Indeed, the following equation was proposed 5a for the valence-electron energy of a two center two-electron heteronuclear bond AB,
ab • eAB = IEA + IEB + a2EAA + b2EAB ...................................................................(1)
where I EX and EAx respectively stand for the ionization energy and the electron affinity of element X.
a2 + b2 = 1 and 7,
the permanent polarity of the AB bond, is given by
I = b2 — a2 = (EAB - EAA) / (EAA + EAB) .
For the enthalpy of a reaction A + +B-^a b one readily obtains:
AHAB = IEA + IEB + a2EAA + b2EAB-IEB-EAB = IEa-EAaI.................................................. (2)
HSAB theory is also useful in predicting the products of metathesis reactions. In 2005 it was shown that even the sensitivity and performance of explosive materials can be explained on basis of HSAB theory.[2]
Ralph Pearson introduced the HSAB principle in the early 1960s.The theory is used in contexts where a qualitative, rather than quantitative, description would help in understanding the predominant factors which drive chemical properties and reactions. This is especially so in transition metal chemistry, where numerous experiments have been done to determine the relative ordering of ligands and transition metal ions in terms of their hardness and softness.The gist of this theory is that soft acids react faster and form stronger bonds with soft bases, whereas hard acids react faster and form stronger bonds with hard bases, all other factors being equal. The classification in the original work was mostly based on equilibrium constants for reaction of two Lewis bases competing for a Lewis acid.
Answer 2; by using the formula given in the question we get
Iodine (I2) and dimethylamine; Values of Ca= 1 , Ea= 1 and Cb= 8.73, Eb= 1.09; ANSWER IS :- 9.46
Trimethylgallinium and Diethylsulfide; Values of Ca= .881 , Ea= 13.3 and Cb=7.4 Eb= .399; ANSWER IS :- 11.028
Delta E= Ea*Eb + Ca*Cb;
Answer C : enthalpy of adduct I is lower than adduct II it means that Generally speaking, acids and bases interact and the most stable interactions are hard-hard (ionogenic character) and soft-soft (covalent character).