Intermolecular Forces - Chemistry PDF

Intermolecular Forces Intramolecular vs. Intermolecular Intramolecular forces are the forces that hold the atoms together in molecules (bonds). Intermolecular forces are the forces between molecules. Both are electrostatic forces. What kind of interactions occur between water molecules?...

Intermolecular Forces Intramolecular vs. Intermolecular Intramolecular forces are the forces that hold the atoms together in molecules (bonds). Intermolecular forces are the forces between molecules. Both are electrostatic forces. What kind of interactions occur between water molecules? intermolecular Types of Intramolecular forces Ionic Bonds – attraction between positive cation and negative anion Covalent Bonds – attraction between atoms sharing electrons Metallic Bonds – attraction of positive metal cations sharing a sea of electrons Intermolecular Forces (IMF) Intermolecular forces are important because they explain many of the properties of substances including state, melting/freezing point, and viscosity, among other things. Covalent and Ionic bonding is about 10-100 times stronger than IMF States of Matter Intermolecular Forces Dipole-Dipole Forces Dipole-dipole forces exist between neutral polar molecules. Polar molecules need to be close together. The partial positive side of one molecule is attracted to the partial negative of another molecule Intermolecular Forces Hydrogen Bonding Special case of dipole-dipole forces. Through experiments it was found that boiling points of compounds with H-F, H-O, and H-N bonds are abnormally high. Intermolecular forces are abnormally strong. H-bonding requires H bonded to an electronegative element (most important for compounds of F, O, and N) Intermolecular Forces London Dispersion Forces (LDF) Weakest of all intermolecular forces. Every molecule and atom has LDF. It is possible for two adjacent neutral molecules to affect each other. The nucleus of one molecule (or atom) attracts the electrons of the adjacent molecule (or atom). For an instant, the electron clouds become distorted. In that instant a dipole is formed (called an instantaneous dipole). The strength of the LDF is dependent on the number of electrons (more electrons – stronger LDF)  Intermolecular Forces Chapter 11 Copyright 1999, PRENTICE HALL 10 London Dispersion Forces