States of Matter

Core Concept – States of Matter

In this tutorial, you will learn about the four main states of matter (solid, liquid, gas, and plasma), as well as some intermediate states of matter, by reading about their properties, applications, and examples.

Topics Covered in Other Articles

Vocabulary for States of Matter

Magnetic field – a region around a magnet or an electric current that describes the magnetic influence on moving electric charges, currents, and magnetic materials. A moving electric charge in a magnetic field experiences a force perpendicular to its velocity.
Matter– anything that has mass and occupies space; it constitutes atoms and compounds, which compose physical and chemical properties. For more in-depth information on the concept of matter, check out this article!
Phase and Matter are occasionally used as synonyms; however, it is possible to form several phases that are in the same state of matter (such as how solids can have different crystalline structures).

What are the States of Matter?

The states of matter refer to the physical forms that matter can take. There are three main states of matter: solid, liquid, and gas. The state of a substance depends on its temperature and pressure. For example, at room temperature and pressure, water is a liquid. But if the water is heated to a high enough temperature, it will become a gas (steam), and if it is cooled to a low enough temperature, it will become a solid (ice). The behavior of matter also changes depending on its state. Solids have a fixed shape and volume, while liquids have a fixed volume but can take the shape of their container, and gases have neither a fixed shape nor a fixed volume. The properties of a substance, such as its density, conductivity, and viscosity, also vary depending on its state of matter.

There are four main states of matter if you include plasma. Additionally, there are many intermediate states, many of which only exist under extreme conditions; in total, there are twenty! Due to their difference in properties being their distinguishing factors, let’s go over some of the states of matter below:

Solids

In the solid state, particles tightly pack together in a fixed arrangement. Due to the strong forces holding them together, the particles of a solid are only able to move back and forth in small vibrations. In other words, they stay in their fixed positions. As a result, solids have the lowest kinetic energy of all the states of matter.

The particles of the compound bind in either an organized, geometric lattice or a random, unstructured shape. The materials present and the conditions in which a solid is created dictate whether it will be a crystalline or amorphous solid. Usually, when conditions are steady (such as slow and gradual cooling/heating), the particles have a chance to align uniformly. However, when there are extreme and rapid temperature changes, an indefinitely shaped solid will most likely be the result.

Solids have a definite shape and volume, meaning they have a fixed position and will not conform to the shape of their container. Because their particles are so densely packed, solids tend to have a high density and are hard to compress further without the use of great external force.

Classes of Solids

Whether or not we realize it, there are so many types of solids all around us—from table salt to a wooden chair! Since the types of forces and bonding between particles can vary, there are different classes of solids. These classes include metals, minerals, (glass) ceramics, organic molecules, composite materials, semiconductors, nanomaterials, and biomaterials. Due to their different force interactions, these categories of solids have different physical and chemical properties. These properties include elasticity, conductivity, light transmittance, plasticity, and more.

Liquids

In the liquid state, particles flow around each other. They are more loosely packed than a solid. Due to the weaker forces holding their particles together, liquids conform to the shape of their container. However, the interaction is strong enough to keep the particles attracted to each other. As a result, liquids are incompressible. This means that liquids have a fixed volume (no matter the shape of their container) as long as the temperature and pressure are held constant. Since there is more particle movement than within a solid, liquids have a higher kinetic energy value.

Solids, when heated past their melting point, can absorb thermal energy, which gets the particles moving. Once enough energy enters the system to weaken the forces keeping them fixed, the particles move more as they transition into the liquid state. Some properties to look at when researching liquids are buoyancy, surface tension, fluidity, and density.

Gases

In the gaseous state, the particles have even more freedom to move than in a liquid. Here, the particles can move in random directions without attracting each other. The molecules have enough kinetic energy that the intermolecular forces holding them together are negligible, which is the reasoning behind their amount of movement. Like liquids, gases do not have a definite shape; therefore, they also conform to the shape of their container. However, unlike liquids, gases are compressible—they do not have a fixed volume. This means that the gas particles will spread out to fill the container they are in. Because of the distance between gas particles, it is common for a colorless gas to be invisible to the human eye. This is why we have ways to detect gases, such as carbon monoxide detectors!

Due to the properties of this state of matter, it can be difficult to mathematically analyze gases. This is why there is the Ideal Gas Law, which sets up conditions for how a gas should act under ‘perfect’ conditions. There are also different mathematical relationships that set up conditions for the behavior of gases such as Boyle’s Law, Charles’ Law, Gay-Lussac’s Law, Henry’s Law, the Combined Gas Law, and Avogadro’s Law.

Pure Gases vs Gas Mixture

A pure gas can be made up of individual atoms (e.g., noble gases like neon and argon), elemental molecules with a single type of atom (e.g., diatomic gases like O₂ and N₂), or compound molecules with multiple types of atoms (e.g., carbon dioxide). A gas mixture, on the other hand, contains a variety of pure gases. A common example of a gas mixture is the air in the earth’s atmosphere. The earth’s atmosphere contains nitrogen, oxygen, argon, and several other gases.

Plasmas

This lesser-known state of matter is a subset of gases. Similar to gases, plasmas do not have a definite shape or volume and have lower density. Again, this means that the particles conform to both the shape and volume of the container in which they are held. However, while gases are made up of molecules with a net charge of zero, plasmas are made up of charged particles. They consist of a freely moving sea of electrons with positively charged nuclei “floating about”. As a result, plasmas can conduct electrical charges and interact with other electromagnetic forces.

A plasma can become a gas in one of two ways. First, being exposed to a big voltage difference (equal or greater than a charge difference of 2) will strip the electrical charge and ionize it, giving it the neutral charge of a gas. Second, by exposing the plasma to high-temperature conditions, the electrons leave the atoms, resulting in free electrons. Since only some electrons are free, this is called partially ionized plasma. In some extreme conditions, it can be assumed that all electrons are free; this is called fully ionized plasma.

Examples of Plasmas

Plasma comprises approximately 99% of the universe. It glows in the form of stars, nebulas, and auroras. In addition, a layer of the Earth’s atmosphere known as the ionosphere is considered to be a plasma. Bolts of lightning in the sky and neon signs in city streets are other examples of plasma.

Video Tutorial on States of Matter

Please enjoy our animated lecture on Phases and States of Matter: The Law of Conservation of Mass.

Bose-Einstein Condensate (BEC)

In 1995, scientists demonstrated a man-made state of matter: Bose-Einstein condensate. It is a group of atoms cooled to near absolute zero (-273.15°C). At this temperature, the atoms do not have free energy to move relative to each other. Therefore, they begin to coalesce into a single quantum state and become identical, behaving as a single atom. Bose-Einstein condensates play a major role in the development of energy-efficient lasers and ultrafast optical switches.

Color Glass Condensate

This type of matter has a theory to it! It supposedly exists inside atomic nuclei when they collide while traveling close to the speed of light. In association with Einstein’s theory of relativity, a high-energy nucleus can appear compressed; as a result, the gluons within the nucleus appear as a wall traveling at the speed of light. The gluon wall’s density increases. The saturated gluon matter is known as the Color Glass Condensate. This state of matter is important because it has been proposed as a universal form of matter to analyze and describe properties of high-energy, strongly interacting particles.

States of Matter in different conditions

Standard Temperature and Pressure

At standard temperature and pressure (STP), most substances exist as gases, but under different conditions, they can take on different states. For example, at low temperatures and high pressures, some substances can exist as a solid, liquid, or gas simultaneously, in a state known as a triple point. Other substances can exist as a solid and a gas at the same time, in a state known as a sublimation. The properties of a substance, such as its density, conductivity, and viscosity, also vary depending on its state of matter. In high school or college-level chemistry, students learn about the different states of matter and how to predict and explain the phase changes between them.

Temperature

The states of matter change when the temperature or pressure of a substance changes. For example, when a substance is heated, the energy of its molecules increases. Increased energy causes them to move faster and farther apart. This can lead to a change in the state of the substance, such as a solid melting to become a liquid or a liquid boiling to become a gas. Similarly, when a substance cools, the energy of its molecules decreases, causing them to move slower and closer together. This can lead to a change in the state of the substance, such as a liquid freezing to become a solid or a gas condensing to become a liquid.

Pressure

The pressure of a substance can also affect its state of matter. For example, increasing the pressure on a gas can cause it to condense and become a liquid. While decreasing the pressure on a liquid can cause it to vaporize and become a gas. These changes in temperature and pressure come from a variety of factors, such as the addition or removal of heat, changes in the volume of the substance, or the presence of other substances that can affect its state.