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What factors affect acid strength and base strength?
This lesson describes the factors that affect acidity and basicity.
The factors below affect acidity and basicity (acronymn ARIO):-
1.Atom -electronegativity and size.
2. Resonance stabilization.
3. Inductive effect – and electronegativity.
4. Orbital type – hybridization
1. Electronegativity and acidity (Atom effect)
Electronegativity is the affinity of electrons by an atom. Electronegativity increases from the left of the periodic table to the right of the periodic table this means that fluorine is the most electronegative element in the periodic table.
2. Size (Atom effect)
Consider the general acid dissociation below:-
H-A = H+ + A–
In the above general equation, the acid (H-A) dissociated to form a proton (H+) and a conjugate base (A-). We will explain the size effect on the conjugate base (A-) in two ways.
– The bigger the conjugate base (A-) the better it can accomodate (spread/hold/hide) electrons (polarization), making it a weaker conjugate base! also the better and making the parent acid (HA) a stronger acid!
– The bigger the conjugate base (A-) the weaker the bond between H-A, making it easier for the “H” of H-A to be donated away, making H-A a stronger acid (remember that acids
Drawing resonance structures review [ Ссылка ]
Hybridization review [ Ссылка ]
3. Resonance Stabilization
Resonance is the reason why ethanoic acid is more acidic than ethanol. If the conjugate base is resonance stabilized, the parent acid is more acidic. Ethanoic acid (acetic acid) produces ethanoate (acetate) which is resonance stabilized, while ethanol produces ethoxide which is not resonance stabilized.
4. Inductive effect
Inductive effect is the electron density pull through bond. When a carboxylic acid or an organic molecule has electron withdrawing elements or Group of elements on the chain, those electron withdrawing elements will attract electron density towards themselves reducing the electron density on the other side of the molecule having an OH making the O-H bond polarized and the more acidic. Let us assume that we have acetic acid, chloroacetic acid, dichloroacetic acid, and trichloroacetic acid. Let us rank these three from the least acidic to the most acidic. We use inductive effect to rank them with the one having the most electron withdrawing groups having the most interactive effect and being most acidic
5. Orbital (Hybridization) stabilization
Hybridization can affect acidity. S orbitals are usually the closest to the nucleus in a shell. Increase in s-character (%) in an orbital tends to increase electronegativity, and in turn better charge stabilization of an anion of a conjugate base formed after ionization of an acid. Please visit the my website at for more and quizes [ Ссылка ]
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