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A presentation that I made with Sam Jangala and David Sundaram for my Chemistry class.
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Instantaneous Dipole-Induced Dipole Forces
By Sam Jangala, David Sundaram & Elisha Lai
Introduction Can be known as:
London Dispersion Forces [LDF]Named after the German-American 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 e-s around a
molecule/atom at any given instant induces a temporary dipole in the molecule
Analogy: Effect of a Magnet on a Pin
A constantly moving magnet (magnetic dipole)
comes close to a pin.
The pin becomestemporarilymagnetized
(induced dipole).
The pin is thenattracted to the
magnet.
The pin losesits attraction to
the magnet as the magnet moves
away from the pin.
δ- δ+
Strength of Forces
Increases across a period
Increases down a group
Strength of Forces
Methane [CH4]
•C-6 protons,6 electrons
Silane [SiH4]
•Si-14 protons,14 electrons
Germane [GeH4]
•Ge-32 protons,32electrons
Increases with the number of protons and electrons because more chance of dipoles forming. Therefore, the boiling points of these compounds also increase.
δ-[1 e-]
δ+[0e-]
Strength of ForcesContinuously varies within a molecule
Daily Life Application #1: Non-Stick 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