# STATES OF MATTER

Almost all matter can be classified as a solid. a liquid or a gas. These are called the three states of matter.

(The fourth state of matter is called ‘plasma: It only exists at high temperatures seldom seen on Earth, and so we won’t consider it further here. even though most of the matter in the universe and most stars are made of plasma.)

 Differences between Solid, Liquid and Gases Solid Liquid Gases Particles are very closely packed together. Particles are closely packed together, but there is still some “wriggle” room. Particles Particles are closely packed together, so little room to move around. Therefore, the particles vibrate one fixed position. Similar to solid, but particles still have some freedom to move around. Particles are free to move around and move past one another. Has a fixed shape and volume – Very inflexible. Often fits the shape of the container – e.g. Water put into a conical flask will have a different shape as opposed to water put into a cup of water. Assumes the shape and volume of the container as well.

Matter is made up of atoms and molecules. An atom is the basic unit of matter. Each element has its own unique atom, which differ from each others by the number of protons in its nuclei. For example, a hydrogen atom has one proton while a helium atom has two protons. A neutral atom has equal number of protons and electrons. The way the individual atoms or molecules(collectively call particles) arrange themselves form the characteristics of the states of matter. Most materials fall under the three states of matter: solid, liquid and gases.

#### SOLID

In a solid, the particles are packed closely together. The inter-atomic forces or inter-molecular are very strong because the distances between the individual particles are very closed together. The particles in a solid vibrate in place within the structure. Since the forces holding the particles are very strong, the particles are not free to move about. This provides the explanation why a solid has a regular shape and fixed volume. Solids has the following properties

• Fixed shape and volume because the particles are held firmly in place within the structure
• Usually hard and rigid
• High density because the particles are packed closely together
• Incompressible because the particles are already closely packed

#### LIQUID

In a liquid, the particles are also closely packed, but a little further apart than solid. The particles in a liquid are not rigidly fixed. They can move to different places. This explains why a liquid can flow but the volume is not very much larger than a solid. Liquid has the following properties

• Fixed volume but not fixed shape.
• High density because the particles are closely packed
• Incompressible because the particles are close together

#### GAS

In a gas, the particles are very far apart. Since the particles are not held in place, a gas can flows like a liquid. However because the particles are far apart, a gas has a volume larger than either its solid or liquid states. A gas has the following properties

• No fixed shape and volume because the particles loosely interact with each other over the very large distance between the particles
• Low density because the particles are far apart
• Compressible because the particles are far apart and can be pushed closer together

### RANDOM MOTION OF PARTICLES

All the motion describe earlier are random. One cannot predict how one individual particle will travel. The only thing that is known is that the average kinetic energy of the particles is directly proportional to the temperature in the kelvin scale. Even though the particles are too small to be observed with the eyes, their effects can be seen in Brownian motion. A model showing Brownian motion can be seen in the clip below: