Chemistry Timeline

Democritus Credited for the creation of atomic theory

Aristotle Didn't believe in atomic theory and taught so otherwise. He believed that everything was created from the four elements; fire, earth, water, and air

John Dalton Credited for improving the atomic theory

James Chadwick Credited for the discovery of neutrons

J.J. Thompson Credited for the discovery of electrons

Robert Andrews Millikan Credited for the discovery of electron charge

Ernest Rutherford Credited for the discovery of protons

Cathode Ray Over the course of three experiments J. J. Thomson discovered the existence of electrons. He did this using a cathode ray tube, which is a vacuum-sealed tube with a cathode and anode on one end that creates a beam of electrons travelling towards the other end of the tube

Gold Foil Experiment Physicist Ernest Rutherford established the nuclear theory of the atom with his gold-foil experiment. When he shot a beam of alpha particles at a sheet of gold foil, a few of the particles were deflected. He concluded that a tiny, dense nucleus was causing the deflections.

Oil Drop Experiment The oil drop experiment was performed by Robert A. Millikan and Harvey Fletcher to measure the elementary electric charge (the charge of the electron). The experiment entailed observing tiny electrically charged droplets of oil located between two parallel metal surfaces, forming the plates of a capacitor.

Plum Pudding Model The Plum Pudding Model is a model of atomic structure proposed by J.J. Thomson in the late 19th century. Thomson had discovered that atoms are composite objects, made of pieces with positive and negative charge, and that the negatively charged electrons within the atom were very small compared to the entire atom.

Rutherford Model The Rutherford model is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger–Marsden experiment which suggested, upon Rutherford's 1911 analysis, that J. J. Thomson's plum pudding model of the atom was incorrect.

Cell Nucleus-Anton Leewenhoek In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells.