Atomic Theory Timeline Project

Democritus

400 BCE

Contribution: Democritus was the first really to propose the idea of the atom. He believed that all mater is composed of invisible particles called "atomos". Model: The solid sphere is the first concept of indivisible particles. Experiment: None

Aristotle

300 BCE

Contribution: Aristotle did not believe in the idea of atoms. He believed that matter was continuous and composed of 5 basic elements: earth, water, air, fire, and ether (which is up in the heavens). Model: No atomic model Experiment: No experiment

John Dalton

1803

Contribution: Dalton made the atomic theory with his own version, which consisted of the idea that atoms of different sizes and masses can combine in fixed proportions to form compounds. Model: Solid Sphere Model Atoms are indivisible. Experiment: Dalton's law of multiple proportions and law of definite proportions.

J.J. Thomson

1897

Contribution: Thomas discovered the electron using the cathode ray tube experiment. This showed that atoms contain smaller particles and are divisible. Model: Plum pudding model Experiment: Cathode ray tube experiment

Albert Einstein

1905

Contribution: Einstein showed that atoms and molecules are real by explaining how tiny particles move in liquids (Brownian motion). Model: Statistical Model of Atoms Experiment: Einstein’s work on Brownian motion provided predictions that were later confirmed.

Ernest Rutherford

1908

Contribution: Rutherford's gold foil experiment led himto the discovery of the atomic nucleus. He found that most of the atom is empty space, with small, dense nucleus at the center. Model: Nuclear model Experiment: Gold foil experiment

Niels Bohr

1913

Contribution: Bohr presented a theory for the hydrogen atom, based on quantum theory that certain physical features only take discrete values. Only in designated orbits do electrons move around a nucleus; if they stray from this, the difference is released as radiation. Model: Planetary Model Experiment: Work on atomic spectra

Werner Heisenberg

1927

Contribution: Heisenberg introduced the uncerteainty principle which states that we cannot simultaneously know the exact postion and momentum of an electron. Which challenged Bohr's idea of fixed orbits. Model: Quantum Model Experiment: Thought experiment in quantum mechanics.

Erwin Schrodinger

1930

Contribution: Schrodinger developed the wave equation, which describes the probability of finding an electron in a given location. This led to the quantum mechanical model of the atom. Model: Quantum model Experiment: Schrodinger's wave equation

Modern Atomic Theory

2000

Contrbution: Further advancements in technology, such as the invention of electron microscopes and particle accelerators, have helped scientists to explore atomic structure in greater detail.