Chemistry - Acids, Bases, and Electronegativity

Electronegativity and Bond Character

• Electronegativity (ΔEN) determines the character of a bond: covalent (ΔEN < 0.4), polar covalent (0.4 ≤ ΔEN ≤ 1.7), or ionic (ΔEN > 1.7)
• Polar covalent bonds have partial positive and partial negative charges

Acid and Base Definitions

Arrhenius Acid and Base

• Arrhenius acid: produces H+ in aqueous solution
• Arrhenius base: produces OH- in aqueous solution

Brønsted-Lowry Acid and Base

• Brønsted-Lowry acid: proton donor
• Brønsted-Lowry base: proton acceptor

Lewis Acid and Base

• Lewis acid: electron pair acceptor
• Lewis base: electron pair donor

Intermolecular Forces

• van der Waals forces: weak, exhibited by all molecules
• Dipole-dipole forces: moderate, exhibited by molecules with a net dipole
• Hydrogen bonding: strong, exhibited by molecules with O—H, N—H, or H—F bonds
• Ion-ion forces: very strong, exhibited by ionic compounds

Trends in Brønsted Acids

• Acidity increases with decreasing ionic radius of M and increasing charge of M
• Acidity increases with increasing electronegativity of E and number of oxo groups

Hard and Soft Acids and Bases (HSAB)

• Hard acids: highly polarizing, exhibit ionic character
• Soft acids: poorly polarizing, exhibit covalent character
• Hard bases: highly polarizable, exhibit ionic character
• Soft bases: poorly polarizable, exhibit covalent character

Anhydrous Oxides

• Nonmetal oxides: acidic in aqueous solution
• Metal oxides: basic in aqueous solution
• Metalloid oxides: amphoteric in aqueous solution

Fajan's Rules

• Summarize the factors affecting polarization in ionic and covalent bonds

Lewis Acids and Bases: HSAB Concept

• Hard acids and bases: exhibit ionic character, have small size and high charge
• Soft acids and bases: exhibit covalent character, have large size and low charge