Intermolecular Forces PDF
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This document provides a summary of intermolecular forces, including London dispersion forces, permanent dipole-dipole forces, and hydrogen bonds. It explains the definitions, examples, and strength of each type of force. The document is aimed at secondary school students.
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Summary INTERMOLECULAR FORCES London forces Permanent Hydrogen Bonds...
Summary INTERMOLECULAR FORCES London forces Permanent Hydrogen Bonds Dipole-Dipole forces Definition Attraction forces between induced or Attaction forces between permanent Structured bonds between permanent dipoles instantaneous dipoles. dipoles: containing Hydrogen (H) atoms bonded to one of the London forces are acting between ALL the Permanent dipole-dipole forces are highly electronegative atoms Fluorine, Oxygen or molecules, but they are only relevant for non- present between polar molecules Nitrogen (F, N, O) polar molecules or for molecules with a big (containing atoms/atom groups with non-polar end. partial charges) Explanation - In atoms and non-polar molecules, electrons - Dipoles created by differences in - Dipoles created by high differences in are in average evenly distributed. electronegativities electronegativities (H vs. F, N or O) - BUT: electrons in atoms or molecules are - Attraction forces between - Formation of weak bonds between partially moving quickly in orbitals: oppositely charged partial charges charged hydrogen atoms and lone pairs of → Formation of instantaneous dipoles: more electrons are on one side of the existing between neighbouring electrons in the F, N, O atoms. atom/molecule leading to the formation of molecules temporary partial charges → These instantaneous dipoles (or ions, or permanent dipoles) can induce new instantaneous dipoles in neighbouring particles: induced dipoles Examples Alkanes, noble gases, halogens HCl, HBr, HI, aldehydes Methanol: HF, H2O, NH3, alcohols Strength of WEAKEST intermolecular force Stronger than London forces, weaker STRONGEST intermolecular force (still about 20x force than Hydrogen bonds weaker than a covalent or an ionic bond!!!) London forces increase: - For large atoms (more polarizable) Hydrogen bonds are stronger as the electronegativity - For longer molecule chains (see below) of the group bonded to the hydrogen atom is increased - For straight chain molecules (see below) 1/1
