SOLIDS

Structure: Solids may be ionic, metallic, simple covalent or giant covalent, but all of these structures have something in common; the smallest particles are not free to move, they are held close together in fixed positions by the forces around them. The only motion allowed is vibration and this is how they absorb energy. A particle in a solid will vibrate more and more as the temperature rises until eventually it has enough energy to break free from the forces holding it in position. This happens at the melting temperature.

Bulk properties:Solids show a definite shape and a definite volume. Unless forces are used that are not commonly found near the earth’s surface, solids can not be compressed.

Liquids

Structure: Liquids are materials in which the smallest particles are as close together as solids, but the particles can slip over each other to change places. They can vibrate, rotate and translate but the forces that hold the particles of liquid close to each other are greater than the forces due to motion that would force the particles away from each other.

Bulk properties:Liquids have no fixed shape except for the shape of the container but do have a fixed volume. Liquids can not be compressed under common pressures.

Gases

Structure: The particles of gas, either atoms or molecules, have too much energy to remain attached to one other. The move by translation, rotation and vibration, but in this case the translational motion is the most important. The particles are on average very far apart and collide incessantly many times a second. Because of the distance between them it is assumed that the forces of attraction between the particles are negligible.

Bulk properties: Materials in the gas phase have no fixed shape, that is, they take on the shape of the container. Gases have no fixed volume, the motion of the particles is so great that the forces of attraction between the particles are not able to hold them together. A certain amount of gas at a pressure of one atmosphere and a volume of ten liters could become five liters if the pressure was increased or would become more than ten liters if the pressure was decreased. The gas expands to fill the container.