University:
East Georgia State College
Course:
CHEM 1211 | Principles of Chemistry I
Academic year:

2023
Views:

167

Pages:

1
Author:

5CelestialChronicle

Intermolecular Forces of Attraction: Attractive forces between molecules and atoms A hydrogen bond occurs when electrons from a highly electronegative atom are partially shared with a positively polarized hydrogen atom Requirements for hydrogen bond formation 1. The covalent bond to hydrogen must be highly polar 2. There must be nonbonding electrons on a highly electronegative atom These requirements restrict hydrogen bond formation to molecules that have hydrogen atoms bonded to fluorine, oxygen, and nitrogen. Examples: water , NH3, CH3OH, HF, CH3NH2 , C6H12O6 Hydrogen bonding is the strongest IMF, but is still only about 5% as strong as a “typical” covalent bond. Dipole- dipole - Interaction of polar molecules with other polar molecules Examples: HCl in water , HBr, CH3Cl London forces (or Dispersion forces) are the net attractive forces generated by temporary charge imbalances (induced dipoles) among molecules. All molecules exhibit London forces, but they are much weaker than the other IMF’s, and are therefore only noticeable in the Nonpolar molecular substances, which employ London forces to stick together. The molecular polarizability is a measure of how easy it is to distort the electron cloud of a molecule. The number of electrons a molecule possesses affects its polarizability; the greater the number of electrons a substance has, the stronger its London force Less polarizability means weaker intermolecular forces Examples: He, hydrocarbons (CH4, C8H18…), I2, CO2 "Like Dissolves Like" Whether or not a given substance dissolves in a liquid depends primarily on three types of intermolecular forces of attraction: 1. Those between solute molecules 2. Those between solvent molecules 3. Those between solvent and solute in the solution A substance dissolves if the forces of attraction between the solvent molecules and the solute molecules are comparable or greater than the solute-solute and solvent-solvent interactions. Substances that dissolve in each other usually have similar types of intermolecular interactions. Polar substances will dissolve in other polar substances. Nonpolar substances will dissolve in other nonpolar substances. Other “ Intermolecular” Forces 1.Ionic - result of electrostatic forces between ions; usually considered an “intra”molecular force examples: NaCl(s), solid sodium nitrate, NaOAc(s) 2.Ion-dipole - interaction of an ion (cation or anion) with a polar molecule examples: dissolving any ionic compound in water Notes: 1.You must be able to first determine whether something is ionic, polar covalent, or nonpolar covalent before you can identify the type of IMF. 2.Once you have identified the type of intermolecular forces present, you should be able to make predictions about boiling point (volatility), melting point, and other physical properties. 3.You should also be able to predict whether one substance will be miscible or soluble with another.