I Intermolecular and Intramolecular Forces section 2 Ch

I. Intermolecular and Intramolecular Forces section 2 Ch. 13 - Liquids & Solids C. Johannesson

Intramolecular Forces • Forces within a molecule (between atoms) • Some covalent bonds are broken more easily than others • Strength depends on distance (bond length) • Size of atoms • Number of shared electron pairs • As the number of shared pairs increases, bond length decreases • Shorter bond=stronger bond • Triple bonds shortest, strongest C. Johannesson

Intermolecular Forces • Attractive forces between molecules • a. k. a. van der Waals forces • weaker than intramolecular forces C. Johannesson

B. Types of IMF C. Johannesson

B. Types of IMF • London Dispersion Forces View animation online. C. Johannesson

London Dispersion Forces • Weak forces that result from temporary shifts in the density of electrons in electron clouds • When 2 nonpolar molecules are in close contact, the electron cloud of one molecule repels the electron cloud of the other molecule • Changes the shape of the other C. Johannesson

C. Johannesson

Dipole-Dipole Forces • Attractions between oppositely charged regions of polar molecules - + View animation online. C. Johannesson

Dipole-Dipole Forces • Polar molecules have a permanent dipole and orient themselves so that oppositely charged regions match up. • Stronger than dispersion forces • If molecules being compared are similar in mass. C. Johannesson

Hydrogen Bonding • Occurs when H is bonded to F, O, or N • Creates a large partially positive charge on the H which is then attracted to the partially negative atom on another molecule C. Johannesson

C. Determining IMF • NCl 3 • polar = dispersion, dipole-dipole • CH 4 • nonpolar = dispersion • HF • H-F bond = dispersion, dipole-dipole, hydrogen bonding C. Johannesson