When Was the Modern Atomic Theory Established?


Martha Robinson

The modern atomic theory is a scientific model that explains the structure of matter. It was developed over time by many scientists, but its establishment can be traced back to the early 1800s.

John Dalton’s Atomic Theory

John Dalton, an English chemist, proposed the first modern atomic theory in 1803. He suggested that all matter is made up of tiny, indivisible particles called atoms. According to Dalton, atoms of the same element are identical in size, mass, and other properties while atoms of different elements have different properties.

Dalton’s theory also stated that atoms combine in simple whole-number ratios to form compounds. This helped explain why chemical reactions occur and how they could be described with formulas.

JJ Thomson’s Discovery of the Electron

In 1897, JJ Thomson discovered the electron using a cathode ray tube experiment. This discovery challenged Dalton’s theory because it suggested that atoms were not indivisible as previously thought.

Thomson proposed a new model of the atom called the “plum pudding” model. According to this model, an atom consisted of a positively charged sphere with negatively charged electrons embedded within it like raisins in a pudding.

Ernest Rutherford’s Discovery of the Nucleus

In 1911, Ernest Rutherford conducted his famous gold foil experiment which led to the discovery of the nucleus. He found that most of the alpha particles passed straight through the foil but some were deflected at large angles suggesting that an atom has a small but dense positively charged nucleus at its center.

Rutherford’s discovery led to a new atomic model known as the “planetary” or “solar system” model where electrons orbit around a central nucleus.

Niels Bohr’s Quantum Model of Atom

Niels Bohr proposed his quantum model of atom in 1913 which explained the spectral lines of hydrogen atoms. According to this model, electrons orbit the nucleus in specific energy levels or shells. Electrons can move from one energy level to another by absorbing or emitting energy.

Bohr’s model was later modified and improved upon by other scientists, but it marked a significant step towards understanding the behavior of atoms and their electrons.


In conclusion, the modern atomic theory was established over time through the contributions of many scientists including John Dalton, JJ Thomson, Ernest Rutherford, and Niels Bohr. Each new discovery and model helped refine our understanding of atoms and their structure leading to new applications in physics, chemistry, and technology.