Atomic theory is the basis of the science of atoms and the basis of chemistry.
History of the atomic theory
The ancient Greek philosopher Heraclitus thought that everything was in a state of flux and change. His compatriot Parmenides, another fifth century Greek, founded the Eleatic school of philosophy and believed that change was impossible, and that everything was the way it was.
The first person to mention the existence of a particle we know as the atom was Democritus. Another fifth century Greek, Democritus searched for the smallest particles into which matter could be divided. He is credited with creating the word, atom, from atomos, meaning not to be cut. He believed that these atoms were created from the same matter, but that their sizes and shapes were different. He believed them to be infinite, always in motion and capable of joining with each other. It was not until John Dalton laid out an atomic theory that is still used in chemistry. Dalton was a British Quaker, who lived from 1766 to 1844. He became a teacher in England at the age o 12. He is known today for this atomic theory, but he also made other discoveries in chemistry and other sciences. Dalton, who was colorblind, brought insights into that disease. He was also well versed as a meteorologist and studies the nature of gases. It was his study of the gases that laid the groundwork for the atomic theory. In 1897, Joseph John Thomson discovered the electron. Thomson, who lived from 1856 to 1940 suggested that the atom was not divisible but it was made up of small pieces called electrons and protons with positive and negative charges. He theorized that the positive and negative charges were equal so that the atom was neutral and had no charge. Ernest Rutherford presented a paper on March 7, 1911 at the Manchester Literary and Philosophical Society in which we described an experiment that confirmed the structure of the atom. The experiment showed that the mass of the atom was in the nucleus and that the rest of the atom was a field of space. In 1913, Neils Bohr went further with this model and suggested that the electrons were in an orbit around the nucleus and that the electrons with the lowest energy orbited closer to the nucleus while those of higher energy orbited farther away.
What is Dalton's atomic theory?
Dalton's atomic theory states that all matters are made of atoms and that these atoms are indivisible and indestructible. Dalton also states that all atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kids of atoms. And, a chemical reaction is a rearrangement of atoms.
Modern atomic theory
Modern atomic theory is built upon Dalton's work, and has remained unchanged for the most part. Because of nuclear reactors, we can now destroy atoms, but they still cannot be destroyed by chemical reactions. Modern science has also noted that there are a variety of kinds of atoms in a single element. These are called isotopes. Isotopes belong to the same element and therefore have the same chemical properties as the main element. Modern atomic theory also includes a quantum model of the atom. The subshells and orbits of the electrons were given quantum numbers to differentiate them depending on the shape of the orbital, its orientation in space and its spin.