Intermolecular Forces
description
Transcript of Intermolecular Forces
![Page 1: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/1.jpg)
Courtesy: labinitio.com
![Page 2: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/2.jpg)
A phase is a homogeneous part of a system in contact with other parts of the system but separated from them by a well-defined boundary.
2 Phases
Solid phase - ice
Liquid phase - water
![Page 3: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/3.jpg)
Gases:•Assumes the volume and shape of its container.•Low Density•Very Compressible•Very Free Motion
![Page 4: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/4.jpg)
Liquids:•Has a definite volume but assumes the shape of its container.•High Density•Only Slightly Compressible•Molecules slide past one another easily.
![Page 5: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/5.jpg)
Solids:•Has definite volume and shape.•High Density•Virtually Incompressible•Molecules vibrate about a fixed position.
![Page 6: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/6.jpg)
•Intermolecular forces are attractive forces between molecules.•Intramolecular forces hold atoms together in a molecule.Intermolecular vs Intramolecular
• 41 kJ to vaporize 1 mole of water (inter)
• 930 kJ to break all O-H bonds in 1 mole of water (intra)
Generally, intermolecular forces are much weaker than intramolecular forces.
“Measure” of intermolecular force
boiling point
melting point
Hvap
Hfus
Hsub
![Page 7: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/7.jpg)
Types of Intermolecular Forces1. Hydrogen Bond (strongest)The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. IT IS NOT A BOND.
A H … B A H … Aor
A & B are N, O, or F
![Page 8: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/8.jpg)
Figure (a): The polar water molecule.Figure (b): Hydrogen bonding among water molecules. Note that the small size of the hydrogen atom allows for close interactions.
![Page 9: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/9.jpg)
Hydrogen Bonding
Electrostatic potential diagrams – red indicates the most electron-rich region and blue indicates the most electron-poor region.
![Page 10: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/10.jpg)
•Hydrogen bonding has very important effect on physical properties.•Note that the nonpolar tetrahedral hydrides of Group 4A (14) show a steady increase in boiling point with molar mass (i.e., going down the group).•But in the other groups the lightest member has the highest boiling point.
![Page 11: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/11.jpg)
Why do H2O, HF, and NH3 break the trend of decreasing molar mass = decreasing boiling point?
Unusually strong hydrogen bonding forces due to two factors: 1.relatively large electronegativity values which leads to especially polar X-H bonds 2.small size of the element, which allows for the close approach of the dipoles, strengthening the intermolecular forces.
Hydrogen bonding is so strong it takes a great amount of energy to overcome attraction and separate the molecules to produce the gaseous state.
![Page 12: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/12.jpg)
Types of Intermolecular Forces
2. Dipole-Dipole Forces
Attractive forces between polar molecules
![Page 13: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/13.jpg)
Types of Intermolecular Forces3. London Dispersion Forces – (weakest)
Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules
ion-induced dipole interaction
dipole-induced dipole interaction
![Page 14: Intermolecular Forces](https://reader036.fdocuments.net/reader036/viewer/2022070406/5681405e550346895dabd0f8/html5/thumbnails/14.jpg)
Intermolecular Forces3. London Dispersion Forces Continued
Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted.
Polarizability increases with:
• greater number of electrons
Dispersion forces usually increase with molar mass.