|Themes > Science > Chemistry > General Chemistry > Matter > Theories of Matter > Theories of Matter|
by Ron Kurtus (revised 5 November 2000)
For years scientists and philosophers have wondered about all the material or matter around us. What is it? Is there any universal explanation for its appearance, properties, and behavior? One theory that explained some of the properties of matter was the Molecular Theory of Matter. This was followed by the Atomic Theory of Matter. There are still being theories developed that try to explain the true structure of matter.
Questions you may have about this are:
Molecular Theory of Matter
The Molecular Theory of Matter states that all matter consists of tiny particles called molecules. These particles are constantly moving and bouncing off each other like billiard balls. This theory provides an explanation of many characteristics of matter, including how heat works and why materials change from solid to liquid to gas.
The Molecular Theory of Matter is also called the Kinetic Theory of Matter, because of the constant movement of the molecules.
In the early 1800s Robert Brown, a botanist, discovered pollen granules suspended in water would move around in a zigzag motion, as if struck by tiny particles. This phenomenon was called Brownian motion. Years later, Albert Einstein explained the motion through the Molecular Theory of Matter, also called the Kinetic Theory of Matter..
The motion of molecules is responsible for the phenomenon of heat. In other words, the faster the molecules are moving, the higher the temperature.
Change of state of matter
Although moving molecules have kinetic energy according to their speed, they are essentially vibrating in place in a solid. The electrostatic attraction between the molecules is much greater than the kinetic energy.
When the molecules speed up or the material is heated sufficiently, the kinetic energy overcome the molecular attraction and the substance changes its state from a solid to a liquid. Likewise, when the kinetic energy of the molecules increases further, the material can change from a liquid to a gaseous state.
Atomic Theory of Matter
Molecules can be broken into smaller particles called atoms. The Atomic Theory of Matter states that all matter consists of extremely small particles called atoms. These atoms are called elements in chemistry, because they are elementary to molecules
Atoms themselves consist of even smaller particles called electrons, protons, and neutrons. A combination of protons and neutrons combine to form the nucleus of an atom.
Solar system model of the atom
A popular model or picture of an atom that explains many of its properties and features is the solar system model of the atom. This model states that electrons rotate around the nucleus, similar to the planets revolving around the sun.
There are newer, more complex models of the atoms now, consisting of such things as probability clouds of electrons and mathematical descriptions. The solar system model is a sufficient explanation for us in our studies.
The Atomic Theory explains electricity. When electrons break away from their nuclei, their motion results in electricity.
For a long time, it was thought that the proton, neutron, and electron were the elementary particles, as well as the smallest. Since the Atomic Theory was formulated, many new particles have been discovered. The new theories concerning these particles and predicted particles attempts to explain every phenomena in physics. This is also called the Universal Theory of Matter.
There are anti-matter particles, that are the mirror image of existing particles. For example, there is the positron, that is a (+) charged electron. There is a (-) charged proton and a neutron that spins in the opposite direction as the standard neutron.
Also, there have been discovered that the proton and neutron themselves are made of even smaller particles, called quarks. These particles are then held together by particles called gluons.
Finally, there is a theory that these sub-atomic particles are not particles at all, but really vibrating strings. This is going beyond the scope of our studies.
The Molecular Theory states that matter consists of small molecules in motion. This explains heat. The Atomic Theory states that matter consists of atoms made of protons, neutrons and electrons. This explains chemistry and electricity. The new sub-atomic theories have even smaller particles, and they try to explain everything.