2.4_physical_properties_post

2.4_physical_properties_post - 2 Physical Properties 1...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 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 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 2. Physical Properties 3 Ion-Ion Forces Ionic bonds are very strong and a large amount of thermal energy is required to break electrostatic lattice forces that act between the positive and negative ions. Ionic compounds are solids at room temperature and have very high melting points. The boiling points of ionic compounds are usually so high that most compounds decompose before they boil. Intermolecular Forces Attractive forces between molecules and ions. Determine bulk properties of matter. Much weaker than intramolecular forces. Several types of forces: Ion-Ion Dipole–dipole Hydrogen “bonds.” Ion–dipole Instantaneous induced dipole (dispersion forces) 2. Physical Properties 4 Ion-Dipole Forces Important in aqueous solutions The magnitude of the interaction energy (E) depends on the charge of the ion ( z ) and the inverse square of the distance ( r ). E = z μ / r 2 Dipole-Dipole Forces Many molecules have permanent dipoles that give rise to intermolecular forces. Although the molecules are in constant motion and their orientations keep changing, the polar molecules will, on average, be oriented so that oppositely charged ends are closer to each other than ends with like charges Because of the combination of attraction and repulsion coupled with random thermal motion dipole-dipole forces are short range in nature, effective only for molecules that are relatively close to each other....
View Full Document

This note was uploaded on 07/18/2011 for the course NE 122 taught by Professor Nano during the Winter '09 term at Waterloo.

Page1 / 25

2.4_physical_properties_post - 2 Physical Properties 1...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online