INTERMOLECULAR FORCES AND ITS EFFECTS TO PROPERTIES OF.pptx

science

1. INTERMOLECULAR FORCES AND ITS EFFECTS TO PROPERTIES OF SUBSTANCES

2. Intermolecular Forces Atoms and molecules in ionic substances are attracted to each other either by sharing or complete transfer of electrons. These attractions keep the molecules and their identities intact.

3. Electronegativity Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical bond. The greater the electronegativity of an element, the stronger it's attractive pull-on electrons.

4. Intermolecular Force (IMF) The force of attraction by which two atoms or two molecules combine to form a molecule or matter. It is basically attractive in nature. It acts between atom and ions also. The intermolecular force varies for solid, liquid and gaseous matter.

5. Table 1: Types of Interaction Type of Interaction Interacting Particles 1. London Dispersion Force (LDF) All molecules (especially nonpolar molecules) 2. Dipole-dipole Forces Polar molecules 3. Hydrogen bond N, O, or F bonded with H atom

6. DIPOLE-DIPOLE FORCES Dipole-dipole forces are attractive forces existing between polar molecules (molecules that exhibit dipole moment), such as HCl. These forces arise due to interaction between oppositely charged ends of polar molecules. The greater the dipole moment of molecules, the greater is the forces of attraction. Dipole-Dipole interactions 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.

7. DIPOLE-DIPOLE FORCES

8. DISPERSION FORCES OR LONDON FORCES (induced-dipole-induced-dipole attraction) London Dispersion Forces are the weakest attractive forces that are formed due to the temporary dipoles induced in nonpolar molecules. Example: if there is an ion or a polar molecule near an atom or a nonpolar molecule, there will be distortion in the electron clouds of the atom of the nonpolar molecule due to the force exerted by the ion or the polar molecule. This distortion will result in temporary dipoles in the nonpolar molecule which is called induced dipole .

9. Induced dipole Induced dipole is the separation of the positive and negative charges in a nonpolar molecule due to the nearness of an ion or a polar molecule. Dipole-induced dipole when the induced dipole is due to the interaction between a polar and a nonpolar molecule.

10. Hydrogen Bond Hydrogen bond is a special type of dipole-dipole interaction between the hydrogen atom in a polar molecule and the highly electronegative atoms, N, O and F in another molecule. The water molecule is a very good example of a substance that exhibits hydrogen bonding.

11. Hydrogen Bond

12. Properties Of Substances Affected By Intermolecular Forces

13. Surface Tension This is the amount of energy required to stretch the surface area of liquids (e.g., 1 cm2). Liquids with high intermolecular forces tend to have high surface tensions. When water is dropped on a waxy surface, it tends to form a round bead to minimize the surface area that it occupies.

14. Viscosity Viscosity is a measure of a liquid’s resistance to flow. The greater the viscosity of a liquid, the more slowly it flows. The viscosity of substances decreases with high temperatures; thus, syrup flows faster when hot.

15. Boiling Point and Melting Point Boiling point depends on the equilibrium vapor pressure exerted by the liquid or solid above the liquid or the solid. This means that the rate of vaporization is equal to the rate of condensation of the substance in a closed container. Vapor pressure also varies with temperature.

16. The graph below shows the effect of temperature on the vapor pressure of water

17. Solubility Solubility is the ability of a substance (solid, liquid, or gas) to dissolve in a given substance (solid, liquid, or gas). The amount of any substance dissolved in a solvent (the substance that dissolves another substance) depends on the types of interaction among molecules, pressure, and temperature. Solubility follows the 'Like dissolves like' rule, where substances with similar properties, including polarity, are more likely to form solutions; for instance, polar molecules dissolve substances with dipoles, while nonpolar substances dissolve nonpolar ones, facilitated by intermolecular forces like dispersion forces.

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