Acidity of simple acids electron density maps

 
Periodic tableGroup 14Group 15Group 16Group 17
Formula

Electron Density Map (calculated)		CH4NH3H2O HF
electronegativity
acidity		H 2.1 C 2.5
not acidic in water		N 3.0
not acidic in water		O 3.5
v weak acid		F 4.0
weak acid

increasing acidity
 
Proton transfer from EH involves
E-H bond breaking: E–H E + H
formation of E– and H+: E + H E– + H+

Relative acidity of EHn can be correlated with
E-H bond polarity (important for C-H, N-H, O-H, H-F)
(red more negative - blue more positive)

more polar more acidic (HF > H2O)

E-H bond strength (important if E in different rows)

longer bond more acidic (HI > HBr > HCl > HF)
HCl 
strong acid
HBr
stronger acid
HI
even stronger acid
Dr Sheila Woodgate
© The University of Auckland 2002