Forces of Attraction Intermolecular Forces

Bonding Forces Forces of attraction that hold atoms together in one structure are intramolecular (inside) forces. metallic (mobile electrons in a solid) covalent (nonmetals sharing electrons) ionic (separate ions in crystal lattice)

Forces Between Particles Forces that exist outside a molecule are called intermolecular forces. (+) to (-) attraction Intramolecular Forces are stronger than intermolecular forces and require more energy to break. Intermolecular attractions cause the molecules to align themselves (+) to (-).

Types of IMFs Different kinds of particles have different types and strengths of attractions. F2 (nonpolar) F2 (nonpolar) London Dispersion Force

Types of IMFs Attractions between polar molecules are stronger than those between nonpolar molecules. CO (polar) CO (polar) Dipole-Dipole Force

Types of IMFs The strongest attraction between covalent molecules is the hydrogen bond, which occurs between H and N, O, or F only. Hydrogen Bond H2O (very polar) H2O (very polar) False

Types of IMFs Charged particles (ions) interact with polar molecules to form an even stronger bond. H2O H2O Na1+ (ion) embed video of electric field response H2O Ion-Dipole Force

Comparison of Forces strength of attraction Are ions present? Are polar molecules present? Ionic Bonds Ion-Dipole Forces Are H atoms bound to N, O, or F? Hydrogen Bonds Dipole-Dipole Forces Dispersion Forces Only no yes yes no no yes yes no True strength of attraction

IMF Observations Intermolecular attractions explain why some substances are solids and others are liquids or gases at the same temperatures. At 300K: NaCl is solid H2O is liquid Cl2 is gas

IMF Observations Ions dissolve in water due to the strength of ion-dipole forces pulling apart the ions from the crystal lattice. False

Intermolecular Force Practice 1) ___________ are always stronger and require more energy to break than ____________. dipole-dipole, ion-dipole intermolecular, intramolecular hydrogen bonds, dispersion forces ion-dipole, ionic bonds C) HB, LDF

Intermolecular Force Practice 2) True or False: London Dispersion Forces result from temporary shifts in the electron density of a nonpolar molecule. True

Intermolecular Force Practice 3) Van der Waals Forces are forces of attraction between covalent molecules. They are divided into: dispersion forces, dipole-dipole forces, and ion-dipole forces dipole-dipole forces, hydrogen bonds, and dispersion forces ionic bonds and hydrogen bonds ion-dipole forces and ionic bonds B) d-d, HB, LDF

Intermolecular Force Practice 4) True or False: Hydrogen bonds are intramolecular (bonding) forces. False

Intermolecular Force Practice 5) A pair of the molecule shown below would likely exhibit which IMF most strongly? London dispersion forces dipole-dipole forces ion-dipole forces hydrogen bonds O F B) dp-dp

Intermolecular Force Practice 6) A pair of the molecule shown below would likely exhibit which IMF most strongly? London dispersion forces dipole-dipole forces ion-dipole forces hydrogen bonds H H A) LDF

Intermolecular Force Practice 7) A pair of the molecule shown below would likely exhibit which IMF most strongly? H N London dispersion forces dipole-dipole forces ion-dipole forces hydrogen bonds D) HB

Intermolecular Force Practice 8) When heat is added to solid water, it is observed that the molecules begin to liquefy. What is happening to the molecules? The molecules to give off heat and take up more space as they overcome hydrogen bonds. The molecules move faster and are able to overcome the intermolecular forces. B) move faster, breaking IMFs

Intermolecular Force Practice 9) Ionic solids typically dissolve into water. This is best explained by: Multiple ion-dipole interactions overcome the force of attraction between ions. Hydrogen bonds between ions and water are weaker than ionic bonds. London dispersion forces overcome the ionic bonds to dissolve the crystal lattice. A) ion-dipole overcoming ionic bonds

Intermolecular Force Practice 10) Methane (CH4) is a gas at room temperature. Explain using IMFs. Since methane has hydrogen bonds, the attractions aren’t strong enough to hold the molecules together. Since methane has polar bonds, the dipole-dipole forces are too weak to hold molecules closely together. Since methane is nonpolar, the only interactions between molecules are very weak. C) nonpolar