The attractive forces between neighbouring molecules in simple covalent substances.
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What are Van der Waals forces?
The attraction between instantaneous and induced dipoles on neighbouring molecules.
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How do Van der Waals forces arise?
Electrons in a molecule are constantly moving, and at any given time, there may be an unequal distribution of electrons creating a temporary dipole on the molecule.
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When do the strength of Van Der Waals increase? (Size of molecule)
When the size of the molecule increases; Molecules with more electrons will create larger induced dipoles.
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Do the m.p and b.p of the noble gases increase or decrease going down the group?
They increase due to the size of the molecule increasing thus having an increase in van der waals attractions making the bonds harder to break apart.
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When do the strength of Van Der Waals increase? (Points of contact)
Increasing the surface area of a molecule increases the amount of contact between electrons on neighbouring molecules thus increasing the strength of the van der waals forces.
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When is a permanent dipole created?
When there is unequal sharing of electrons within a covalent bond (When two atoms have different electronegativity values)
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What is a hydrogen bond?
The attraction between the lone pair on a very electronegative atom (N,O,F) on one molecule and a hydrogen on a neighbouring molecule in which the hydrogen is covalently bonded to a very electronegative atom.
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Why are some compounds soluble and others are not?
Covalent compounds which can form hydrogen bonds are generally soluble in water.
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Why does ice float on water?
Ice has a lower density than water; the hydrogen bonds in ice are more ordered (fixed) and the water molecules are further apart leading to a more open structure.
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What forces of attraction exist between gas molecules?
There aren't any forces of attraction.
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Explain why water has a higher than expected boiling point.
A large amount of energy is required to break the hydrogen bonds between water molecules.
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Explain why iodine has a higher boiling point than bromine.
Iodine has more electrons than bromine so the van der waals forces of attraction are stronger between iodine molecules.
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Explain why the liquid alkanes increase in viscosity as the carbon chain increases in length.
The number of electrons increases as the carbon chain increases so VDWs are stronger making it less fluid in the liquid state.
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Explain why ethanol mixes with water.
Ethanol has OH groups which can form hydrogen bonds with water moelcules.
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Explain why bromine mixes with hexane.
Bromine and haxane are both non-polar.
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Explain why sodium chloride dissolves in water.
Sodium chloride is an ionic substance which is polar and water is polar.
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Other cards in this set
Card 2
Front
What are Van der Waals forces?
Back
The attraction between instantaneous and induced dipoles on neighbouring molecules.
Card 3
Front
How do Van der Waals forces arise?
Back
Card 4
Front
When do the strength of Van Der Waals increase? (Size of molecule)
Back
Card 5
Front
Do the m.p and b.p of the noble gases increase or decrease going down the group?
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