Chemistry 14: Polar Molecules

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Chemistry 14 Polar Molecules

• Christopher Chui

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Polarity

• A polar covalent bond occurs when a shared pair
  of electrons is attracted more strongly to one of
  the atoms of the bond
• Dipole is another name for a polar molecule
• A dipole moment is a property of a polar molecule
• Partial charges within a molecule are indicated
  by d
• Dipole moment m depends upon the size of the
  partial charges and the distance between them, m
  Qd
• Melting point and boiling point are related to
  dipole moment

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Weak Forces

• Weak attractive forces between the protons of one
  atom and the electrons of another atom are van
  der Waals forces
• Intramolecular forces hold atoms together in a
  molecule while intermolecular forces hold
  different molecules together
• Dipole-dipole attraction exists between molecules
  that are permanent dipoles
• A nonpolar molecule may become an induced dipole
• Two nonpolar molecules may be attracted to each
  other
• Dispersion forces (London forces) result from
  temporary dipoles
• Van der Waals attraction can result from 1)
  dipole-dipole forces, 2) dipole-induced dipole
  forces, 3) dispersion forces

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Ligands

• A complex ion is formed when polar molecules or
  negative ions cluster around a central positive
  ion
• The polar molecules or negative ions are ligands
• The number of points of attachment of the ligands
  around a central positive ion is called the
  coordination number
• Water is the most common ligand
• A bidentate ligand attaches at two points
• Use the prefixes di-, tri-, tetra-, penta-, and
  hexa- to indicate the number of each kind of
  ligand in a name

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Naming Complex Ions

• Neutral molecules carbonyl, ammine, nitrosyl,
  aqua
• Anions bromo, cyano, chloro, fluoro, iodo,
  hydroxo, oxalato, oxo, thio, thiosulfato
• Metal complexes cuprate, aurate, ferrate,
  plumbate, argentate, stannate
• Complex ions are named 1) ligands first, in
  alphabetical order with prefixes 2) central ion
  3) ate ending, if the ion is negative 4) Roman
  numeral
• Ligands in the formulas of complex ions are
  written in a different order from ligands in the
  names

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Coordination Compounds-1

• It is possible to have a complex with a net
  charge of zero in a coordination compound
• If a complex ion occurs in the formula of a
  coordination compound, place the whole complex
  ion in brackets
• Transition metals have partially filled d
  orbitals that can become involved in bonding
• The colors of many complex ions are the result of
  the splitting of the d orbitals. Energy is
  absorbed as electrons move from the lower to
  higher energy levels
• The bonding structure of complex ions is similar
  to that of salts

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Coordination Compounds-2

• Gemstones have trace amounts of transition metal
  ions
• Beryl emerald Cr, aquamarine Fe
• Corundum ruby Cr, sapphire Fe or Ti
• Quartz amethyst Fe
• The bond formed when both electrons in the shared
  pair come from the same atom is a coordinate
  covalent bond
• Chromatography is a separation method that
  depends on the polarity of substances. The mobile
  phase, or mixture to be separated, passes over
  the stationary phase
• Thin layer chromatography may be used to separate
  amino acids
• Gas chromatography is used to analyze volatile
  liquids and mixtures of gases