Liquids
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The physical properties of the states are controlled by the strengths of intermolecular attractions.
Stronger attractions make the molecules closer together, forming liquids.
Even stronger ones pack the molecules together, forming solids.
The main types of intermolecular attractions are dipole-dipole attractions, hydrogen bonds, and London forces.
Dipole-dipole attractions are the attractions between polar molecules.
Opposite poles of different molecules attract each other.
They are about 1% as strong as a covalent bond.
Hydrogen bonds are similar to dipole-dipole attractions, but they involve hydrogen since it is very electronegative.
F-H, O-H, and N-H bonds are very polar and molecules that have those bonds generally attract each other strongly.
They are about 5% as strong as a covalent bond.
London forces are responsible for attractions in nonpolar molecules.
Since electrons are constantly moving, the movement of electrons in one particle influences electrons in another.
Sometimes, the electrons may even synchronously move all the one side, creating a short-lived dipole, or instantaneous dipole.
General Properties
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Compressibility
In a liquid or a solid, most of the space is taken up by the
molecules, and therefore, it is very difficult to compress them into a smaller volume by applying pressure.
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Diffusion
Diffusion occurs rapidly in gases, slowly in liquids, and hardly at
all in solids.
This is because there is less space in between molecules in liquids and solids for a substance to diffuse through.
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Retention of Volume and Shape
Gases can change their volumes and shapes depending on the pressure and the container.
Liquids generally don't change their volumes but can change their shape depending on the container.
Solids hardly can change their volumes or shapes.
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Surface Tension
A characteristic of liquids is surface tension.
Attractions felt at the liquid's surface and those within are different.
Molecules at the surface want to move back into the center.
This can make it look like a skin because you can fill a glass above the rim.
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Wetting
This is the spreading of a liquid across a surface.
Because of surface tension, beads of liquid form where it was spread.
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Evaporation
Liquids and solids both have a tendency to evaporate.
This involves changing state from liquid to gas or solid to gas.
The change of state from solid to gas directly is called sublimation and occurs with substances like dry ice (frozen CO2).
Temperature changes the rate of evaporation.
The higher the temperature, the higher the rate of evaporation, until it reaches the boiling point, where all of the liquid or solid is changed to gas.
