John Dalton (1803)

Dalton proposed the first modern atomic theory. He believed that all matter is made of tiny, indivisible particles called atoms, which cannot be created or destroyed. Each element has its own kind of atom with a specific mass, and chemical reactions involve the rearrangement of these atoms.

J.J. Thomson (1897)

Thomson discovered the electron using the cathode ray tube experiment. He proposed the Plum Pudding Model, where negatively charged electrons were scattered within a positively charged sphere — like raisins in a pudding.

Ernest Rutherford (1911)

Rutherford’s gold foil experiment showed that atoms have a small, dense, positively charged nucleus at the center. He concluded that electrons orbit this nucleus, and most of the atom is empty space. This overturned the plum pudding model.

Niels Bohr (1913)

Bohr improved Rutherford’s model by suggesting that electrons move in fixed orbits (energy levels) around the nucleus. He explained how electrons could absorb or release energy to jump between these levels — which helped explain atomic spectra.

Quantum Mechanical Model

Erwin Schrödinger (1926)

Schrödinger developed a mathematical model of the atom, using wave equations to describe the behavior of electrons. His model replaced the idea of fixed orbits with orbitals — regions where electrons are likely to be found. This is the basis of the modern atomic model.

Werner Heisenberg (1927)

Heisenberg introduced the Uncertainty Principle, which states that it's impossible to know both the exact position and momentum of an electron at the same time. This supported the idea that electrons exist in probability clouds, not fixed paths.