1. Physical Inorganic Chemistry : THE STRENGTH OF ACIDS & BASES
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2. 1. The Bronsted-Lowry Concept
Acid Strength is a measure for the tendency of an acid to lose proton : An acid is called to be stronger as the tendency increases.
Base Strength is a measure for the tendency of an acid to gain proton : A base is called to be stronger as the tendency increases.
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3. HF HCl HBr HI CH4 NH3 H2O HF Acid strength increases
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4. The concept is essentially based on electrostatic interaction between the corresponding acids and bases
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5. HA + H2O H3O+ + A-
[H3O+][A-]
Ka =
[HA]
- ∆Ho/RT
Ka = e
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6. Acid Conjugate Base K H2SO3 HSO3- 1.72 x 10-2 H3PO3 H2PO3- 1.60 x 10-2
HNO2
NO2-
4.00 x 10-4
H2CO3
HCO3-
4.30 x 10-7
SO3=
6.24 x 10-8
HPO4=
6.20 x 10-8
H2S
HS-
5.70 x 10-8
HCN
CN-
7.20 x 10-10
NH4+
NH3
5.50 x 10-10
CO3=
5.60 x 10-11
PO43-
4.80 x 10-13 S=
1.20 x 10-15
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7. 2. The Lewis Concept
Acid Strength is a measure for the tendency of an acid to accept an electron pair to form chemical bond : An acid is called to be stronger as the tendency increases.
Base Strength is a measure for the tendency of a base to donate an electron pair to form chemical bond : A base is called to be stronger as the tendency increases.
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8. The Strength of Bases
Donor of Electron Pair
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9. The ability of a base to furnish a pair of electrons to an acceptor depends on :δ- δ+
The more negatively charged the donor atom, the more effective the chemical bond formed
THE NEGATIVE PARTIAL CHARGE OF THE DONOR ATOM
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10. δ- δ+ Involvement of the Donor in Bond Multiplicity
Capacity of the Groups Attached to the Donor
THE NEGATIVE PARTIAL CHARGE OF THE DONOR ATOM
Polarizability of the Donor
Concentration of the Donor Electron Pair
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11. Acceptor of Electron Pair
The Strength of Acids
Empty Orbital
Acceptor of Electron Pair
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12. The ability of an acid to gain a pair of electrons from a donor depends on :
The more positively charged the acceptor atom, the more effective the chemical bond formed
THE POSITIF PARTIAL CHARGE OF THE ACCEPTOR ATOM
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13. The more empty orbitals available in the acceptor atom, the more effective the chemical bond formed
THE EMPTY ORBITALS AVAILABLE IN THE ACCEPTOR ATOM
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14. The concept is essentially based on a covalent interaction between the corresponding acids and bases
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15. THE CONCEPT OF HSAB HARD AND SOFT ACIDS AND BASES
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16. ? The Goldschmidt (1935) : Geochemical Ore Classification
Nickel (Ni), zinc (Zn), and copper (Cu) ores are exclusively found as sulfides, whilst aluminum (Al) and calcium (Ca) are usually found as oxide and carbonate, respectively. ?
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17. An acid = an electron pair acceptor A base = an electron pair donor
The Lewis concept of acids and bases involves covalent interaction to form a covalent (coordination) bond :
An acid = an electron pair acceptor
A base = an electron pair donor
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18. Polarizability
The capacity of a group of atoms in a molecule and/or an ion to polarize its electron. δ- δ+
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19. The Elements Li Be B C N O F Na Mg Al Si P S Cl K Ca Sc Ti V Cr Mn FeCo Ni Cu Zn Ga Ge As Se Br Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi -
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20. The Elements Elements tend to form bases Elements tend to form acidsLi Be B C N O F Na Mg Al Si P S Cl K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi -
Elements tend to form acids
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21. Elements tend to form bases
Harder Base
Electronegativity factors
Softer Base N O F P S Cl As Se Br Sb Te I
Size factor
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22. Elements tend to form acids
Harder Acid
Electronegativity factors Li Be B C Na Mg Al Si K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Softer Acid
Size factor
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23. Hard & Soft Acids Li Be B C Na Mg Al Si K Ca Sc Ti V Cr Mn Fe Co Ni CuZn Ga Ge Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Hard Acid
Soft Acid
Borderline
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24. The HSAB Concept : HSAB classification of metal ions (acids) :
Perason, R.G., Journal of American Chemical Society, 1963, 85, 3533–3539.
HSAB classification of metal ions (acids) :
class (a) metal ions :
class (b) metal ions
Alkali : H+, Li+, Na+, K+, Rb+, and Cs+,
Heavier transition metals of lower oxidation states :
alkaline earth: Be2+, Mg2+, Ca2+, Sr2+, and Ba2+,
Cu+, Ag+, Hg+, Hg2+, Pd2+, and Pt2+.
Lighter transition metals of higher oxidation states : Ti4+, Cr3+, Fe3+, and Co2+.
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25. HSAB classification of bases (ligands) :
Tendency to complex with class (a) metal ions :
Tendency to complex with class (b) metal ions
N >> P > As > Sb
N << P < As < Sb
O >> S > Se > Te
O << S < Se < Te
F > Cl > Br > I
F < Cl < Br < I
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26. class (a) metal ions : class (b) metal ions
Tendency to complex with class (a) metal ions :
Tendency to complex with class (b) metal ions
N >> P > As > Sb
N << P < As < Sb
O >> S > Se > Te
O << S < Se < Te
F > Cl > Br > I
F < Cl < Br < I
class (a) metal ions :
class (b) metal ions
H+, Li+, Na+, K+, Rb+, Cs+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Ti4+, Cr3+, Fe3+, and Co2+.
Cu+, Ag+, Hg+, Hg2+, Pd2+, and Pt2+.
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27. Hard Acids
Hard Bases
Soft Acids
Soft Bases
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28. The HSAB Concept : Hard Acids prefer to form complex with Hard Bases and Soft Acids prefer to form complex with Soft Bases
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29. HSAB Classification of Lewis Acids and Bases
Hard
Borderline
Soft
ACIDS
H+, Li+, Na+, K+, Rb+, Cs+, Be2+, Mg2+, Ca2+, Ba2+, Cr3+, SO3, BF3.
Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, SO2, BBr3.
Cu+, Ag+, Au+, Tl+, Hg+, Pd2+, Cd2+, Pt2+, Hg2+, BH3.
BASES
F-, OH-, H2O, NH3, CO32-, NO3-, O2-, SO42-, PO43-, ClO4-.
NO2-, SO32-, N3- Cl-, C6H5N, SCN-
H-, R-, CN-, CO, I-, R3P, C6H6, R2S
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30. Thank you
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