Molecular Theory, States of Matter, and Material Properties
Molecular Theory of Gases
The scientific theory explains the performance of gases. Scientists Clusius, Maxwell, and Boltzmann developed this theory in the eighteenth century. Gases are composed of a large number of tiny particles, too small to see with a microscope. These particles occupy a very small volume compared to the gas container. When they collide, no energy is lost.
The movement of these particles is determined by two types of forces: attractive forces, which tend to keep particles together, and repulsive forces, which tend to push them apart.
States of Matter
- Solid: Particles are close together with small gaps. Forces hold the particles in fixed positions, though they vibrate.
- Liquid: Particles remain at distances similar to those in solids but are less strongly bound. This allows them to slide over each other, giving them mobility and allowing them to adapt to the shape of their container (fluid).
- Gas: Particles are far apart. Attractive forces are very weak, and the particles move in all directions, colliding with the container walls.
State Changes
- Fusion: The transition from a solid to a liquid state. The reverse process is called solidification.
- Vaporization: The transition from a liquid to a gaseous state. This can occur in two ways:
- Evaporation: Occurs on the surface of a liquid at any temperature.
- Boiling: A tumultuous vaporization that occurs throughout the liquid mass. Each liquid has a specific boiling temperature at a given pressure.
- The transition from a gas to a liquid state is called condensation.
- Sublimation: The direct transition from a solid to a gas. The reverse process is called reverse sublimation. At atmospheric pressure, only a few substances, such as iodine or naphthalene, sublime.
Properties of Materials
All objects around us are made of matter. Matter occupies space and has mass. A portion of matter considered in isolation is a material. Matter is anything that occupies space and has mass.
Material: A specific type of matter.
General and Specific Properties
- General Properties: Properties like mass do not provide information about the type of substance.
- Specific Properties: Depend on the class of substance, not its quantity or form.
Mass and Volume
- Mass: Measures the amount of matter in a body. It is a characteristic of materials and does not depend on shape. A material is closed when its mass remains constant.
- Volume: Indicates the amount of space occupied. It does not depend on the shape or degree of division but may depend on factors like pressure or temperature.
Density
Density is the ratio between mass and volume. The density of a substance is the mass corresponding to a unit volume.
Aggregation States of Matter
- Solid: Fixed volume and shape. Cannot be compressed and does not flow. Solids are called crystals if their particles are ordered and amorphous if not.
- Liquid: Fixed volume but not a fixed shape. Compressible and flows.
- Gas: Occupies the entire volume of its container. No fixed shape, spreads easily, and is easily compressible.