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2.4_physical_properties_post

2.4_physical_properties_post - Physical Properties...

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2. Physical Properties 1 Physical Properties Intermolecular Forces An intermolecular attractive force is any force that causes otherwise independent atom, molecules or ions to cluster together. Intermolecular forces are responsible for phase changes such as condensation and solidification, and these forces must be overcome during changes such as melting and vaporization. Dipole Moments The dipole moment ( μ ) is a measure of a molecules molecular dipole. The SI unit for dipole moment is the coulomb meter (C m), but a much smaller unit the debye (D) is commonly used for molecules. It is defined as the magnitude of the charge Q at either end of the molecular times the distance of separation. μ = Q x r 1 D = 3.33 x10 -30 C m Dipole Moment (D) Electro- negativity Difference between atoms Dipole Moment (D) Electro- negativity Difference between atoms Dipole Moment (D) Electro- negativity Difference between atoms HF 1.82 1.8 H 2 O 1.85 1.2 NH 3 1.47 0.8 HCl 1.08 1.0 H 2 S 0.97 0.4 PH 3 0.58 0.0 HBr 0.28 0.8 AsH 3 0.20 0.1 HI 0.44 0.4 SbH 3 0.12 0.2
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2. Physical Properties 2 The dipole moment increases with increasing electronegativity difference between the bonded atoms. This is expected, since bond polarities also increase with increasing electronegativity differences. net dipole = 1.85 net dipole = 1.47
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