Acidity and Bascitity

• Lewis: An electron pair acceptor is an acid and an electron pair donor is a base
• Bronsted-Lowry: A proton donor is an acid while proton acceptor is a base
• • The more stable the conjugate base, A-, is then the more the equilibrium favours the product side (Ka > 1), i.e. more dissociation of H-A
  • More dissociation of H-A then the stronger H-A is as an acid
• • The larger Ka implies more dissociation of HA and so the stronger the acid.
  • The larger Ka is, the more negative the pKa so the lower the pKa, the stronger the acid.
• What factors affect the stability of the conj. base?

  Electronegativity.  When comparing atoms within the same row of the periodic table, the more electronegative the anionic atom in the conjugate base, the better it is at accepting the negative charge.

  Size: the bigger the atom, the more likely the electron cloud can accommodate the negative charge

  Resonance: resonance helps delocalize the charge and spread it out
• A convenient way to look at basicity is based on electron pair availability.... the more available the electrons, the more readily they can be donated to form a new bond to the proton and, and therefore the stronger base.
• Key factors that affect electron pair availability in a base, B?

  Electronegativity.  When comparing atoms within the same row of the periodic table, the more electronegative the atom donating the electrons is, the less willing it is to share those electrons with a proton, so the weaker the base

  Size. The larger the atom the weaker the H-X bond and the lower the electron density making it a weaker base.

  Resonance.  Delocalization across 2 electronegative atoms makes it the electrons less available than when they localized on a specific atom