Summary
Highlights
The atomic model has undergone significant changes over time as scientific knowledge and evidence have developed.
Democritus proposed that matter was made of small, hard, indivisible particles called 'atomos,' meaning 'uncuttable.'
John Dalton established that all matter consists of tiny, indivisible, and indestructible atoms. He theorized that atoms of the same element are identical in mass and properties, and cannot be converted into atoms of another element.
J.J. Thomson discovered the electron through cathode ray experiments, revealing that atoms were not indivisible. He proposed the 'plum pudding' model, where negatively charged electrons were embedded in a positively charged sphere.
Ernest Rutherford discovered the proton and the nucleus. His gold foil experiment showed that atoms have a dense, positively charged nucleus at the center, with electrons orbiting in mostly empty space, disproving Thomson's model.
Niels Bohr improved Rutherford's model, proposing that electrons orbit the nucleus in specific, fixed energy levels or shells, similar to planets orbiting the sun. Electrons in these orbits have quantized energy and do not lose energy.
Erwin Schrödinger developed the quantum mechanical model, suggesting that electrons do not move in fixed orbits but rather exist in electron clouds, where their exact position is uncertain but their probability of location can be determined. This model is currently the most accurate.