Lesson 2 Intermolecular Forces.pptx
- 2. Section Objectives 1. Define intermolecular force. 2. Describe and differentiate the types of intermolecular forces.
- 3. Review Polar Polar molecules occur when two atoms do not share electrons equally in a covalent bond. Examples of polar molecules include: water - H2O ammonia - NH3 sulfur dioxide - SO2 hydrogen sulfide - H2S ethanol - C2H6O
- 4. In a polar covalent bond, one atom spends more time with the electrons than the other.
- 5. Nonpolar When molecules share electrons equally in a covalent bond there is no net electrical charge across the molecule. Examples of nonpolar molecules include: • any of the noble gasses: He, Ne, Ar, Kr, Xe (These are atoms, not technically molecules.) • any of the homonuclear diatomic elements: H2, N2, O2, Cl2 (These are truly nonpolar molecules.) • carbon dioxide - CO2 • benzene - C6H6
- 6. In a nonpolar covalent bond, the atoms share electrons equally with one another.
- 7. Dipole - a molecule in which a concentration of positive electric charge is separated from a concentration of negative charge.
- 9. Intermolecular Forces • Forces of attraction between molecules are called intermolecular forces (IMF). • These are forces that act between individual molecules that hold them close together as in a solid or a liquid.
- 10. Intermolecular forces can be grouped for convenience into Dipole-dipole forces, Ion- dipole forces, Dispersion forces and Hydrogen bonds.
- 11. The attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.
- 13. London dispersion forces (LDF) - Is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction.
- 15. London dispersion forces are weak intermolecular forces and are considered van der Waals forces. Temporary dipoles can occur in molecules when the electrons that constantly orbit the nucleus occupy a similar location by chance
- 16. • Dispersion (London) Forces exist between non polar molecules as a consequence of random electron positions (temporary dipole) • Much weaker than real dipole • Larger molecules are more likely to exhibit London forces
- 17. • This is why non-polars have lower melting and boiling points
- 20. Dipole-dipole forces are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule. Dipole-dipole forces have strengths that range from 5 kJ to 20 kJ per mole. The partially positive end of a polar molecule is attracted to the partially negative end of another.
- 21. Dipole-dipole forces - force that occurs between two polar molecules. They occur when the slightly positive end of one polar molecule is attracted to the slightly negative end of another polar molecule.
- 23. - result when two dipolar molecules interact with each other through space. When this occurs, the partially negative portion of one of the polar molecules is attracted to the partially positive portion of the second polar molecule
- 26. - these forces exist when polar molecules are attracted to ions. The positive pole is attracted to a negative ion (anion), while the negative pole is attracted to a positive ion (cation).
- 27. - are generated between polar water molecules and a sodium ion. The oxygen atom in the water molecule has a slight negative charge and is attracted to the positive sodium ion. These intermolecular ion-dipole forces are much weaker than covalent or ionic bonds.
- 31. Hydrogen bonding Hydrogen bonding is a special type of molecular attraction between the hydrogen atom in a polar bond and nonbonding electron pair on a nearby small electronegative ion or atom (usually F, O or N).
- 32. Hydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine. Also, when hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed.