London Dispersion Forces
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Why do non-polar moleucles have no permanent separation of charge within bonds?
shared electrons pulled equally by two atoms
What do noble gases exist as?
non-polar particles
How are london dispersion forces formed?
• electrons behave like mobile clouds of negative charge • density of cloud may be greater at one moment • over one region temporary/instantaneous dipole formed • influences electron distribution in neighbouring atoms • causes induced dipole weak • forces of attraction (london forces) occur between opposite ends of two temporary dipoles in molecules
london forces are the — form of intermolecular force
weakest
the strenght of london forces — with moledulcar size Why?
increases greater number of electrons within a molecule increases probability of dipole developing
trend in melting/boiling points in non-polar molecules
• low melting/boiling points • london forces are only forces that exist between non-polar molecules • little energy required to break weak london foces and separate molecules from each other
hydrogen bonding
attraction when a molecule contains a hydrogen covalently bonded to a very electronegative atom (F, N, O)
hydrogen bonding effect on boiling point
makes boiling point much higher