The basic concept behind atomic structure theory is that all matter is composed of infinitesimal building blocks called atoms. Atoms themselves can also be subdivided into smaller particles. Most of an atom’s mass is concentrated in a central nucleus, which is comprised of protons and neutrons. Protons have a net electrical charge that’s positive while neutrons lack electrical charge; negatively charged electrons orbit the nucleus. The precise number of these protons and electrons, and the dynamics of their relationship to each other, determine the composition of the various elements of the periodic table.
1. A Brief History Of Atomic Theory
While we may think of atomic structure as a discovery that’s relatively new, the idea that all matter can be subdivided into small indivisible units has been around since the fifth century BCE when the Greek philosophers Democritus and Leucippus first proposed the theory. Galileo believed in atoms, too, although he pictured them as the actualisation of mathematical points. Sir Isaac Newton also postulated the existence of atoms when he theorised about perpetual motion in his mechanical universe.
It wasn’t until the English chemist John Dalton began experimenting with the thermal expansion of atmospheric gases that atomic theory began to resemble the body of knowledge with which scientists are now familiar. Dalton was the first scientist to contend that atoms of any given element differ in mass and size but that all atoms of a given element are identical to one another.
In 1913, the Danish physicist Niels Bohr further refined atomic theory. Bohr postulated that electrons only occupy certain orbits around the atomic nucleus and that these orbits are associated with measurable energy levels.
2. Contemporary Atomic Theory
Today, we understand that atoms are not the smallest particles but are themselves composed of even smaller particles. Protons and neutrons, for example, are made up of subatomic particles called quarks. Quarks have mass, but they also have a number of other unusual properties that make them behave as much like light waves as they do like matter. As Albert Einstein theorised, at the subatomic level, mass and energy are really the same thing.