2.2.8-2.2.9 - Intermolecular Forces
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What are intermolecular forces?
forces between molecules
What are intramolecular forces?
forces inside a molecule (bonds)
What physical properties do intermolecular forces affect largely?
melting and boiling points
Why do stronger intermolecular forces equal higher melting and boiling points?
because it means more energy is required to overcome them
Why is melting/boiling point a physical change?
because no bonds are being formed or broken
When are intermolecular forces overcome?
in a change of state
Where do London Dispersion forces exist?
in all molecules
Why do London Dispersion forces exist in all molecules?
because all molecules have electrons
What are London Dispersion forces?
an instantaneous induced dipole (partially pos or neg area of the molecule)
How is a dipole temporarily created with London Dispersion forces?
the electron cloud is temporarily shifted in such a way that a temporary dipole is created
What factors affect the size of the London Dispersion forces?
number of electrons in the molecule, size/volume of the electron cloud, shape of the molecule
What do more electrons mean in London Dispersion forces?
a larger attractive force
What does the size/volume of the electron cloud mean in London Dispersion forces?
more electrons allow for more charge available to move around within the molecule
What impact does the shape of a molecule have in London Dispersion forces?
longer chains have a larger usable surface area over which forces can be applied
What will larger London Dispersion forces result in when no other intermolecular forces are present?
higher melting/boiling point
What are dipole-dipole forces between?
Two molecules that are polar
How does the strength of dipole-dipole forces compare to that of London Dispersion forces?
they have a stronger force of attraction
How do the dipoles involved in dipole-dipole forces compare to those of London Dispersion forces?
they are permanent
What will polar molecules have that is significantly higher than non-polar molecules, even with equally sized electron clouds?
a higher melting/boiling point
What type of intermolecular force is hydrogen bonding?
dipole-dipole forces
When is hydrogen bonding possible?
when H is bonded to N, O or F
What is happening in hydrogen bonding?
the H in a molecule is attracted to the neg region in another molecule of the same substance, then H loses valence electron in a covalent bond and only a proton remains
What does only having the single proton during hydrogen bonding lead to?
a very strong attractive force to areas of high electron density (high electronegativity)
What leads to a lower volatility?
stronger intermolecular forces