The first advocates for an atomic theory were Leucippus and Democritus, Greek philosophers, in the fifth century B.C. They suggested that matter is made of particles that are too small to be seen. Democritus proposed that if you kept cutting a substance in half into smaller and smaller pieces, eventually you would come to the smallest particles that are no longer able to be split.
Their model specified five main parts: 1) Matter is composed of atoms and these are separated by empty spaces through which they move, 2) Atoms are solid, homogenous, indivisible, and unchangeable, 3) All visible changes in matter are a result of the changes in groups of atoms, 4) there are different types of atoms, and 5) matter reflects the properties of the atoms contained in it.
Kinetic Theory of Matter
This proposed model is not so different from today’s kinetic theory of matter (particle theory) that we have today. The four main ideas from the kinetic theory of matter today are: 1) All matter is made of small particles, 2) the particles are always moving (and therefore have kinetic energy), 3) the particles have spaces between them, and 4) adding heat to matter makes the particles move faster (have higher kinetic energy).
The atom is considered to be the basic building block of all matter, as it is the smallest amount of matter that can retain the characteristic properties of an element. This excludes the subatomic particles that makeup atoms, however, as they can be associated with multiple different elements. An element is a substance that cannot be broken down into simpler substances through chemical processes. These elements can combine to form compounds. These compounds are made of molecules, which can be combinations of atoms of a single element or multiple elements.
A Variety of States
These elements and compounds exist in a variety of states. The three primary states of matter are Solids, Liquids, and Gases. Particle theory is able to help explain the properties of these materials through what the particles in each state do.
In Solids particles are held tightly and are packed closely together, giving the matter a definite shape. These particles are in fixed positions, allowing it to maintain that shape, however these particles vibrate in place and have a very low kinetic energy.
In Liquids the particles are fairly close together with some attraction between them, which allows liquids to have an indefinite shape. They are able to move around in all directions but this movement is limited by the attraction between particles, making it so that they have higher kinetic energy than particles in solids. Since there can be so many particles in a small volume it makes it difficult to compress liquids, though their volume can change depending on temperature changes.
Gases have particles with very little attraction between them, making it so that gases also have an indefinite shape. They expand to fit any container since the particles are free to move around in any direction, making them the highest kinetic energy of the three states. Gases are easily compressed since there are only a few particles in a large volume.
Matter can change states from solid to liquid, liquid to gas, gas to solid, and any combination thereof. There are six total changes of state that can occur between these states. Melting occurs when a solid turns into a liquid due to an increase in kinetic energy of the particles. If kinetic energy is lost, a gas can become liquid through condensation, and a liquid can turn into a solid through freezing. Evaporation occurs when a liquid turns into a gas, also due to an increase in kinetic energy. Gas can turn into a solid, though this does not happen often, this is called deposition and occurs when there is a stark loss of kinetic energy in the particles. The opposite of that, when a solid turns into a gas, is called sublimation and happens when there is a stark gain in kinetic energy of the particles.
However, those are just the more common states of matter and their changes. In the last century and a half, we have discovered five different exotic states of matter. The oldest discovery was in 1879 with the discovery of Plasma, which is a superheated form of a gas that can generate and affect electric and magnetic fields due to the separation of the atomic nuclei from their electrons. The next discovery was in 1911 with superconductors, this is a state occurs where certain metals are cooled to low temperatures to allow electricity to flow with no resistance. In 1938 superfluids were discovered next, these are liquids cooled to near absolute zero and flows without friction. These superfluids can even climb up the sides of a container and drip down the sides. The next discovery was in 1995 with the Bose-Einstein condensate, originally theorized in the 1920’s and 30’s, this matter is only formed at temperatures close to absolute zero. At that temperature, all of the atoms in the material begin to act as a single particle. The most recent discovery, in 2000, is the Quark-gluon plasma. This is a state where protons and neutrons dissolve into quarks that move between particles called gluons that carry the strong force.
Smallest to Largest
Innovations in the last 150 years such as: x-rays, the electron microscope, particle accelerators, and many others have helped us get closer to seeing the smallest building blocks of matter. The basic and applied research in each of those innovations has been able to culminate together and show that quarks, leptons, gauge bosons, and scalar bosons are the smallest particles, collectively called Elementary Particles. Quarks are part of the building blocks for electrons and protons in atoms. Then those atoms can form bonds with one another in order to create molecules. These molecules, when combined in the tens of millions, can create cells. Cells then can become the building blocks of organisms like you and I. Molecules can also combine into inorganic matter that can be used to create anything from buildings to pyramids, even Mount Everest. This scales even further, extending to Earth and other planets orbiting a larger sun. In the size of a galaxy, Earth and other planets and even suns are the particles that make up a galaxy.
To help understand how particles work at the vastly different scales where they exist, humans have developed models to describe particle behavior at these different scales. This helps us to better understand their nature and to design products and develop methods that productively use particles. Look for future blogs posts where we’ll delve into particle models and how they are used.
Want To Explore Further?
To learn more about Particle Theory:
Leucippus and Democritus, http://chemed.chem.purdue.edu/genchem/history/leucippus.html
Mann, Adam. “Confirmed: New Phase of Matter Is Solid and Liquid at the Same Time.” National Geographic, 8 Apr. 2019, www.nationalgeographic.com/science/2019/04/new-phase-matter-confirmed-solid-and-liquid-same-time-potassium-physics/
“Particle Theory.” Particle Theory – Home, www.le.ac.uk/se/centres/sci/selfstudy/particle01.html