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.. . . . : N N : H . . H FORMAL CHARGE Unbonded Bonded Number of All One half of = valence electrons unshared + all shared in the neutral electrons electrons atom Formal Charge . NH2- . 6e- 5e- ( Formal Charge = 5 - 4 - 2 = -1 )
When drawing a Lewis Diagram remember these rules. LEWIS DIAGRAMS SHOW IT ALL ! - all atomsincluding hydrogens - all bonds (lines not dots ) - all unshared pairs ( dots ) - allformal charges - all atoms with octets ( except H ) - the correct number of electrons ( count! )
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
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 (): the vector sum of the individual bond dipole moments in a molecule • reported in debyes (D)
are due to differences in electronegativity. depend on the amount of charge and distance of separation. In debyes, = 4.8 x (electron charge) x d(angstroms) Bond Dipole Moments
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 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.
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
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, HNO3, HClO4, and H2SO4 • 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, Ka, for this equilibrium are
pKa pKa = - log Ka Strong acid = large Ka = small pKa Weak acid = small Ka = large pKa
Acid Strength • Strong Acid • Conjugate base is weak • pKa is small • Weak Acid • Conjugate base is strong • pKa is large
Base Strength • Strong Base • Conjugate acid is weak • pKa is large • Weak Base • Conjugate acid is strong • pKa 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