A Revolutionary History of the Atom – Theories and Models
The History of the Atom, at least as far as scientists and philosophers are concerned, began with the Ancient Greeks and their theories on the nature of matter and time. During this time period, there were two prevailing theories as to how the universe was formed and how everything interacted within it. The first theory was proposed by Empedocles, who believed that matter was composed of four elements – earth, water, air, and fire – that came together to form all matter, including living things.
Dalton’s Atomic Theory
In 1803, John Dalton proposed his atomic theory based on the following observations: (1) all matter is composed of atoms, (2) atoms are indestructible and indivisible, (3) atoms of different elements have different weights, (4) atoms combine in simple whole number ratios to form compounds, (5) in a chemical reaction, atoms are rearranged, not created or destroyed. This theory was able to explain the law of conservation of mass and the law of definite proportions. However, it did not explain why atoms of different elements have different weights or how they could interact with each other.
J.J. Thomson's model: Plum Pudding model
J.J. Thomson's Plum Pudding model was one of the first models of the atom. In this model, Thomson proposed that atoms were made up of negatively charged electrons embedded in a sphere of positive charge. This model helped to explain why atoms are electrically neutral.
Rutherford & Bohr
In 1911, Ernest Rutherford proposed a model of the atom that was based on his experimental observations. He suggested that atoms were composed of a small, dense nucleus surrounded by electrons. In 1913, Niels Bohr expanded on Rutherford's model by proposing that electrons orbit the nucleus in specific shells. This model helped to explain the emission spectra of atoms.
Erwin Schrödinger's model
In 1926, Erwin Schrödinger published a paper proposing a wave equation for electrons in atoms. This was a major breakthrough in quantum mechanics, as it explained many strange behaviors of subatomic particles that had defied explanation up to that point. In his model, electrons are not particles but rather waves spread out over space. This explains why they can be in multiple states at the same time (quantum superposition). It also explains why they sometimes act like particles and other times like waves (wave-particle duality).
The Discovery of Protons and Neutrons
In the early 1900s, scientists discovered that atoms were not indivisible after all. In fact, they found that atoms were made up of smaller particles called protons and neutrons. This discovery led to a revolution in our understanding of the atom.