FORMAL%20CHARGE

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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 )
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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! )
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Rumus Kimia

• Rumus empirik
• Rumus Molekul
• Rumus struktur
• Rumus struktur lengkap
• Rumus struktur panjang (expanded)
• Rumus struktur termampatkan (condensed)

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Rumus Struktur pada senyawa siklis sikloheksana

• Expanded formula

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Rumus Struktur pada senyawa siklis sikloheksana

• Polygon formula(condensed formula)

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Rumus Struktur pada senyawa siklis sikloheksana

• Condensed formula

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Contoh Molekul siklis
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Beberapa cara penulisan struktur
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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)

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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)

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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.

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Polar and Nonpolar Molecules

• these molecules have polar bonds, but each has a
  zero dipole moment

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Polar and Nonpolar Molecules

• these molecules have polar bonds and are polar
  molecules

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Polar and Nonpolar Molecules

• formaldehyde has polar bonds and is a polar
  molecule

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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
  

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Dipole-Dipole
gt
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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.
  

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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.

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Dispersions
gt
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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

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H Bonds
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Boiling Points and Intermolecular Forces
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ASAM DAN BASA
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Brønsted-Lowry Theory of Acids and Bases

• Acid Proton Donor
• Base Proton Acceptor

Conjugate Acid Base Proton Conjugat
e Base Acid - Proton
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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

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Weak Acids and Bases

• Acetic acid is a weak acid
• it is incompletely ionized in aqueous solution

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Lewis Theory of Acids and Bases

• Acid Electron-Pair Acceptor
• Electrophile
• Base Electron-Pair Donor
• Nucleophile

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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

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Weak Acids and Bases
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Acidity Constant (Ka)
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pKa
pKa - log Ka Strong acid large Ka
small pKa Weak acid small Ka large pKa
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Relative Acid Strength
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Acid Strength

• Strong Acid
• Conjugate base is weak
• pKa is small
• Weak Acid
• Conjugate base is strong
• pKa is large

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Base Strength

• Strong Base
• Conjugate acid is weak
• pKa is large
• Weak Base
• Conjugate acid is strong
• pKa is small

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Position of equilibrium

• Favors reaction of the stronger acid and stronger
  base to give the weaker acid and weaker base

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Position of equilibrium

• Stronger acid and stronger base react to give
  weaker acid and weaker base