FORMAL CHARGE Unbonded Formal Charge NH 2 Number

FORMAL CHARGE Unbonded Formal Charge = NH 2 - Number of valence electrons in the neutral atom . . N: . Bonded All One half of unshared + all shared electrons 5 e- ( Formal Charge = 5 - 4 - 2 = -1 ) . . H. . N: . . H 6 e-

When drawing a Lewis Diagram remember these rules. 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! )

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

Rumus Struktur pada senyawa siklis – sikloheksana l Expanded formula

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

Rumus Struktur pada senyawa siklis – sikloheksana l 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 ( ): 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, = 4. 8 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: • Base: Proton Donor 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, HCl. O 4, and H 2 SO 4 • Strong base - completely ionized in aqueous solution. Examples are: – Li. OH, Na. OH, 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

Weak Acids and Bases

Acidity Constant (Ka)

p. Ka = - log Ka Strong acid = large Ka = small p. Ka Weak acid = small Ka = large p. Ka

Relative Acid Strength

Acid Strength • Strong Acid – Conjugate base is weak – p. Ka is small • Weak Acid Conjugate base is strong – p. Ka is large –

Base Strength • Strong Base Conjugate acid is weak – p. Ka is large – • Weak Base Conjugate acid is strong – p. Ka 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