staircase memory tool! handy moving up this while of IMFs increase Intermolecular Forces (IMFs) Forces (not bonds!)BETWEEN molecules IMFs are much weaker than real bonds Three important types to know Have important effects on boiling points What to Know: definition of forces which substances have which forces how these forces effect boiling points *** m’c = molecules *** HYDROGEN “BONDING” staircase memory tool! Attraction of m’c to other m’c due to dipole moments of polar m’c that include an H bonded to either an N, O or F. The positive H side of one m’c attracted to negative N, O or F side of a different m’c & vice versa (even stronger than dipole-dipole) Polar m’c (m’c with dipole moments) that have an H bonded to either an N, O or F have them These m’c “stick together” even more strongly, and so are harder to boil; this leads to higher boiling points than m’c without hydrogen bonds. **Please forgive the terrible job we chemists did naming these forces & remember that hydrogen bonds are not really bonds, they’re IMFs! handy DIPOLE – DIPOLE FORCES Types of IMFs London Dispersion Dipole-Dipole Hydrogen Bonding moving up this Attraction of m’c to other m’c due to dipole moments of polar m’c. Positive side of one m’c attracted to negative side of a different m’c & vice versa (strong) Polar m’c (m’c with dipole moments) have them These m’c “stick together” more, and so are harder to boil; this leads to higher boiling points than m’c without dipole-dipole IMFs while LONDON DISPERSION FORCES of IMFs increase Attraction of m’c to other m’c due to gravity and instantaneous or temporary dipoles (very weak) All m’c have them Higher molar mass, higher boiling point Strength