Instantaneous Dipole Induced Dipole Forces By Sam Jangala, David Sundaram & Elisha Lai
Introduction Can be known as: London Dispersion Forces [LDF] Named after the GermanAmerican physicist Fritz London
Dispersion Forces Part of van der Waal’s forces Weakest type of attractive force Found between atoms/molecules The unequal distribution of es around a molecule/atom at any given instant induces a temporary dipole in the molecule
Analogy: Effect of a Magnet on a Pin
The pin loses its attraction to the magnet as the magnet moves away from the pin.
A constantly moving magnet (magnetic dipole) comes close to a pin.
The pin is then attracted to the magnet.
The pin becomes temporarily magnetized (induced dipole).
Strength of Forces
Increases down a group
Increases across a period
Strength of Forces δ-[1 e-] δ+[0e-]
•C-6 protons,6 electrons
•Si-14 protons,14 electrons
•Ge-32 protons,32 electrons
Increases with the number of protons and electrons because more chance of dipoles forming. Therefore, the boiling points of these compounds also increase.
Strength of Forces Continuously varies within a molecule
Daily Life Application #1: NonStick Pans Polytetrafluoroethane [PTFE] Commonly known as Teflon
LDF between oil/grease &
PTFE are much weaker than those present in the oil/grease itself
Therefore, oil/grease doesn’t stick to the PTFE pan
Daily Life Application #2: Graphite Lead in Pencil Sheets of carbon atoms are held together by LDF
LDF easily overcome Therefore, the sheets slide over each other when you write