The Phases of Matter

The Phases of Matter

Matter can exist in several distinct forms which we call phases. We are all familiar with solids, liquids and gases. Whether a substance is a solid, liquid or gas depends on the potential energy in the atomic forces holding the particles together and the thermal energy of the particle motions. The pressure on the subtance also has an effect on the phase.

Solids

Crystaline Solids

Crystaline solids are characterised by a long-range order. The atoms are closely packed on lattice points held in in place by atomic bonds. The internal energy of the atoms is not sufficient to allow the atoms to break away from their lattice positions. Examples of crystaline solids include semiconductors, quartz, salt, etc.

Amorphous Solids

Amorphous Solids are still closely packed together but lack the translational symmetry of crystaline solids. However, even amorphous solids have relatively good spatial ordering, especially over small distances, (10-100 molecules)

Liquids

As the material is heated, the internal energy is increased and the atoms are no longer tied to their lattice positions but can move relative to each other although the atoms are still closely packed together.

Gases

A gas is matter in which the molecules are widely separated, move around freely, and move at high speeds. Examples of solids include the gases we breathe (nitrogen, oxygen, and others), the helium in balloons, and steam (water vapor).

The solid, liquid and gas phases of matter.
Plasmas

Eventually, given enough heat, the electrons and nucleus become separated and into positively, charged ions and negatively charged electrons. This soup of ions and electrons is known as a plasma

Phase Diagrams

The phases of the material can be recorded for many different pressures and temperatures. Plotting the phases, whether the material is solid, liquid or gas for many different pressures and temperatures we can build up a phase diagram for the substance.

Phase Diagram for water