Electronegativity

Electronegativity and Bond Polarity Dipole Moments

Acids and Bases BrØnsted-Lowry Acids and Bases A BrØnsted-Lowry acid is a proton donor. A BrØnsted-Lowry base is a proton acceptor. H+ = proton

Formal Charge Used for electron ‘book-keeping’ in molecules Sometimes atoms have different numbers of bonds than their ‘usual’ number FC = # of valence electrons – (# of bonds to atom + # of nonbonding electrons) Example: DMSO

Structure and Bonding Resonance These structures are called resonance structures. A double headed arrow is used to separate the two resonance structures. Resonance allows certain electron pairs to be delocalized over several atoms, and this delocalization adds stability

Structure and Bonding Drawing Resonance Structures Rule [1]: Two resonance structures differ in the position of multiple bonds and nonbonded electrons. Rule [2]: Two resonance structures must have the same number of unpaired electrons. Rule [3]: Resonance structures must be valid Lewis structures.

Structure and Bonding Drawing Resonance Structures Curved arrow notation shows the movement of an electron pair.

Structure and Bonding Resonance Hybrids A “better” resonance structure is one that has more bonds and fewer charges.

Structure and Bonding Drawing Resonance Hybrids

Acids and Bases Reactions of BrØnsted-Lowry Acids and Bases A BrØnsted-Lowry acid base reaction results in the transfer of a proton from an acid to a base. Strong acids have weak conjugate bases (and vice-versa)

Acids and Bases Reactions of BrØnsted-Lowry Acids and Bases Curved arrow notation. Equilibrium arrows.

Acids and Bases Acid Strength and pKa The more readily a compound donates a proton, the stronger an acid it is. Acidity is measured by an equilibrium constant

Acids and Bases Acid Strength and pKa Various pKa values: HCl, HCN, H2O, CH3COOH, CH4

An acid will donate a proton to the conjugate base of a weaker acid The conjugate base of a weaker acid will remove the proton from a stronger acid

Predicting if acid-base reactions will occur Water (pKa = 15.74); acetylene (pKa = 25). Which is the stronger acid? Does hydroxide ion react with acetylene? (It’s useful to identify acid, base, conj. acid, conj. base)

Acids and Bases Lewis Acids and Bases A Lewis acid is an electron pair acceptor. A Lewis base is an electron pair donor; lone pair or an electron pair in a  bond. A BrØnsted -Lowry base always donates this electron pair to a proton, but a Lewis base donates this electron pair to anything that is electron deficient.

Acids and Bases Lewis Acids and Bases Any species that is electron deficient and capable of accepting an electron pair is also a Lewis acid. Common examples of Lewis acids: BF3 and AlCl3.

Acids and Bases Lewis Acids and Bases Lewis acid-base reactions illustrate a general pattern in organic chemistry. Electron-rich species react with electron-poor species. In the simplest Lewis acid-base reaction one bond is formed and no bonds are broken. This is illustrated in the reaction of BF3 with H2O. H2O donates an electron pair to BF3 to form a new bond. electrophile nucleophile

Acids and Bases Lewis Acids and Bases

Noncovalent interactions between molecules Dipole-Dipole Forces Dispersion Forces

Hydrophilic / Hydrophobic