6.3 Intermolecular forces Flashcards
what is an intermolecular force?
weak interactions between dipoles of different molecules
what holds atoms in a molecule together?
strong covalent bonds
what holds molecules together?
weaker intermolecular forces
what are the three types of intermolecular force?
induced dipole-dipole interactions (London forces)
permanent dipole-dipole interactions
hydrogen bonding
what molecules have London forces?
ALL MOLECULES
both polar and non-polar
outline how London forces are formed?
at any random instant, an instantaneous dipole is formed with the movement of electrons in an atom
this instantaneous dipole induces a dipole on a neighbouring atom
the induced dipole induces further dipoles on other neighbouring atoms
these molecules then attract each other
the more electrons in a molecule
the larger the London force
the stronger the London force
why does the boiling point increase when the number of electrons increases?
more electrons means more London forces are formed between molecules
the attraction between molecules is now stronger so needs more energy to overcomeq
what is permanent dipole-dipole interactions?
interactions between the permanent dipoles in different polar molecules
why do polar molecules require have higher boiling points?
they have London forces
AND
permanent dipole-dipole interactions
therefore stronger attraction between molecules
so more energy is needed to overcome
what is a simple molecular lattice?
molecules held together by weak intermolecular forces
atoms of these molecules are held together by strong covalent bonds
why does a simple molecular lattice have a low melting and boiling point?
weak intermolecular forces between molecules require little energy to overcome
when a simple molecular lattice is broken apart when melted what is broken?
the weak intermolecular forces are broken
the strong covalent bonds do not break
what are the two types of simple covalent structures?
polar
non-polar
solubility in non-polar simple molecular substances
can dissolve in non-polar solvents
cannot dissolve in polar solvents
