Chapter 3 - Chapter 3. Acids and Bases Acids and...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 3. Acids and Bases Acids and Bases Brønsted acids and Bases What has been transferred acid base protons acid Lewis acids and Bases base acid base electrons acid base Curved ­arrow nota:on 1. Showing the electron flow from the source to des:na:on 2. Conserva:on of total charge Electron ­pair displacement reac:ons Derive resonance structures O H3C N O H3C N O O Lewis Acid ­Base Associa:on and Dissocia:on Associa:on Dissocia:on Note that the total charge is conserved Lewis acid ­base reac:on Nucleophile (nucleus ­loving, Lewis base): dona:ng electrons Electrophile (electron ­loving, Lewis acid): accep:ng electrons Brønsted acids ­base reac:on Equilibria in acid ­base reac:ons Review of free energy and chemical equilibrium (Recita:ons at this week) Strength of Brønsted acids The strength of a Brønsted acid is determined by how well it transfers a proton to a standard Brønsted base. The standard base tradi:onally used for comparison is water. Amphoteric compounds Amphoteric compounds: compounds that can act as either acids or bases. Example: water pKa (table 3.1) Rela:onship of Structure to Acidity (Brønsted acids) 1.  The element effect: increase toward higher atomic number of atom within a group of the periodic table or within a row of the periodic table; 2. The charge effect: increase in acidity that results from increasing posi:ve charges on the atom bonded to the acidic hydrogen; 3. The polar effect: polar groups affect the acidity through their interac:ons with the charged species in the acid ­base equilibrium. The Element Effect Bond dissocia:on energy, ioniza:on poten:al, electron poten:al Energy required Bond dissocia:on energy Ioniza:on poten:al Electron affinity Free energy change The Charge Effect H3O+ pKa=  ­1.7 H2O pKa= 15.7 NH4+ pKa=9.25 NH3 pKa= 35 The Polar Effect Energy stabiliza:on causes acidity increase Posi:on of EWG affects the acidity Key Points •  Concepts of Lewis acid and base; •  General ideas of curved ­arrow nota:on; •  Lewis acid ­base associa:on and dissocia:on reac:ons; •  Acid ­base reac:ons (Brønsted and Lewis); •  Nucleophile and leaving groups; •  pKa and rela:ve strength of acids and bases; •  pKa affected by the elements, charges, and polarity of the molecule. ...
View Full Document

This note was uploaded on 08/24/2010 for the course CHEM 3351 at Colorado.

Ask a homework question - tutors are online