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Democritus was an ancient Greek philosopher who lived from 460 BC to 370 BC. He was an influential pre-Socratic philosopher and pupil of Leucippus, who formulated what is thought to be the first atomic theory. Some people consider him to be the father of modern science. It is hard to separate his theories from those of Leucippus, since they are always mentioned in the same texts, but their theories have very different basis.

Democritus was the first to suggest existence of atoms. He belived atoms were indestructible and invisible.

John Dalton pictures atoms as tiny indestructibles particles, with no internal structure, also the same year he gives his atoms theory.

Ludwig Edward Boltzmann is one of the foremost theoretical physicists of the latter nineteenth century. A vigorous advocate for the existence of atoms, he made monumental contributions to the kinetic theory of gases and established the statistical nature of the second law of thermodynamics.Austrian physicist Ludwig Boltzmann, who established the statistical nature of the second law of thermodynamics.

Discovered the electron. This later leades to his "plum pudding" model. He pictured electrons embedded in a sphera of positive electric charge.

This provides a clear concept for the wave nature of electron and also brought across the concept of orbitals, or the three dimensional spaces. A scientist who played an important part in the merging of Quantum theory with atomic structure is Werner Heisenberg. He not only is responsible for the inclusion of quantum mechanics to the atomic theory, but also in providing a theory for structure of co-ordination complexes.

Suggests that an atom has a central nucleus and that electrons move in orbit.

Einstein was one of the fathers of the atomic age. He was one of the greatest scientists of all time. In 1905 Einstein contributed three papers to Annalen der Physik (Annals of Physics), a German scientific periodical. Each of them became the basis of a new branch of physics.

Einstein treated matter and energy as exchangeable. Albert Einstein became famous for the theory of relativity, which laid the basis for the release of atomic energy.

In 1905 Albert Einstein formulates Special Theory of Relativity.

He established law of mass- energy equivalence; through his famous formula E=mc²

Einstein calculates how the movement of molecules in a liquid can cause the Brownian motion.

Atoms have a small, dense, posetivily charge nucleus with electrons moving around it

A simple definition of Bohr’s atomic model is: electrons orbit the nucleus at set distances. When an electron changes orbits, it does so in a sudden quantum leap. The energy difference between the initial and final orbit is emitted by the atom in bundles of electromagnetic radiation called photons. This model was proposed in 1913 by Niels Bohr and was really an expansion on the Rutherford model of 1911. The Rutherford model had several flaws that the Bohr model overcame.

Belived the electron moves in a circular orbit at fixed distances from the nucleus.

Did experiments to find quantity of charge carried by an electron. He ended up calculating the mass of an alectron.

Propose that moving particles like electrons have some properties of waves. After a few years exoerimental evidence supported the idea.

Wolfgang Pauli was an Austrian theoretical physicist noted for his work on spin theory and quantum theory, and for the important discovery of the Pauli exclusion principle, which underpins the structure of matter and the whole of chemistry.

Developed mathematical equations to describe the motion of electrons in atoms, leading to the electron cloud model.

Confirms the existence of neutrons, wich have no charge.