Transcript Chemistry 14: Polar Molecules Christopher Chui 5/24/2016

Chemistry 14:
Polar Molecules
Christopher Chui
5/24/2016
Polar Molecules - C. Chui
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Polarity
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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
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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
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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
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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
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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
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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
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