FORMAL CHARGE Formal Charge N :..... N :.... H H NH 2 - Bonded Unbonded Number of All One half of = valence electrons unshared + all shared in the neutral electrons electrons atom ( Formal Charge = = -1 ) 5e - 6e -

LEWIS DIAGRAMS SHOW IT ALL ! - all atoms including hydrogens - all bonds (lines not dots ) - all unshared pairs ( dots ) - all formal charges - all atoms with octets ( except H ) - the correct number of electrons ( count! ) When drawing a Lewis Diagram remember these rules.

Rumus Kimia Rumus empirik Rumus Molekul Rumus struktur  Rumus struktur lengkap  Rumus struktur panjang (expanded)  Rumus struktur termampatkan (condensed)

Rumus Struktur pada senyawa siklis – sikloheksana Expanded formula

Rumus Struktur pada senyawa siklis – sikloheksana Polygon formula (condensed formula)

Rumus Struktur pada senyawa siklis – sikloheksana Condensed formula

Contoh Molekul siklis

Beberapa cara penulisan struktur

Molekul polar dan Nonpolar To determine if a molecule is polar, we need to determine –if the molecule has polar bonds –the arrangement of these bonds in space Molecular dipole moment (  ):Molecular dipole moment (  ): the vector sum of the individual bond dipole moments in a molecule –reported in debyes (D)

Bond Dipole Moments are due to differences in electronegativity. depend on the amount of charge and distance of separation. In debyes,  x  (electron charge) x d(angstroms)

Molecular Dipole Moments Depend on bond polarity and bond angles. Vector sum of the bond dipole moments. Lone pairs of electrons contribute to the dipole moment.

Polar and Nonpolar Molecules these molecules have polar bonds, but each has a zero dipole moment

Polar and Nonpolar Molecules these molecules have polar bonds and are polar molecules

Polar and Nonpolar Molecules –formaldehyde has polar bonds and is a polar molecule

Intermolecular Forces Strength of attractions between molecules influence m.p., b.p., and solubility; esp. for solids and liquids. Classification depends on structure. –Dipole-dipole interactions –London dispersions –Hydrogen bonding

Dipole-Dipole =>

Dipole-Dipole Forces Between polar molecules Positive end of one molecule aligns with negative end of another molecule. Lower energy than repulsions, so net force is attractive. Larger dipoles cause higher boiling points and higher heats of vaporization.

London Dispersions Between nonpolar molecules Temporary dipole-dipole interactions Larger atoms are more polarizable. Branching lowers b.p. because of decreased surface contact between molecules. =>

Dispersions =>

Hydrogen Bonding Strong dipole-dipole attraction Organic molecule must have N-H or O-H. The hydrogen from one molecule is strongly attracted to a lone pair of electrons on the other molecule. O-H more polar than N-H, so stronger hydrogen bonding

H Bonds

Boiling Points and Intermolecular Forces

ASAM DAN BASA

Brønsted-Lowry Theory of Acids and Bases Acid:Proton Donor Base:Proton Acceptor Conjugate Acid: Base + Proton Conjugate Base: Acid - Proton

Strong Acids and Bases Strong acid - completely ionized in aqueous solution. Examples are: –HCl, HBr, HI, HNO 3, HClO 4, and H 2 SO 4 Strong base - completely ionized in aqueous solution. Examples are: –LiOH, NaOH, KOH, Ca(OH) 2, and Ba(OH) 2

Weak Acids and Bases Acetic acid is a weak acid –it is incompletely ionized in aqueous solution

Lewis Theory of Acids and Bases Acid: Electron-Pair Acceptor – Electrophile Base: Electron-Pair Donor – Nucleophile

Weak Acids and Bases The equation for the ionization of a weak acid, HA, in water and the acid ionization constant, K a, for this equilibrium are

Weak Acids and Bases

Acidity Constant (K a )

pKa a pK a = - log K a a Strong acid = large K a = small pK a Weak acid = a Weak acid = small K a = large pK a

Relative Acid Strength

Acid Strength Strong Acid –Conjugate base is weak – pK a is small Weak Acid – Conjugate base is strong – pK a is large

Base Strength Strong Base – Conjugate acid is weak – pK a is large Weak Base – Conjugate acid is strong – pK a is small

Position of equilibrium Favors reaction of the stronger acid and stronger base to give the weaker acid and weaker base

Position of equilibrium Stronger acid and stronger base react to give weaker acid and weaker base