-
390 BCE
Democritus
Everything is composed of atoms
Between atoms is an empty space
Physically, but not geometrically indivisible
Atoms are indestructible -
Antoine Lavoisier
Lavoisier is nicknamed the “Father of Chemistry,” because he discovered how oxygen is combustible. He also named the elements, carbon, hydrogen, and oxygen. Additionally, he was the first person to come up with a list of 33 elements. -
John Dalton
Dalton originally created his Atomic Theory for an article he wrote. Later in 1808, he expanded his atomic theory, and came up with the idea that atoms could be universally distinguished based on their atomic weight. He also came up with the idea that atoms can’t be created or destroyed. -
Dmitri Mendeleev
Periodic law
Started periodic table of elements
used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered -
Eugen Goldstein
spent most of his career at the Potsdam Observatory,
discharge tubes, and named the light emissions studied by cathode rays
Won hughes medal in 1908 -
J.J. Thomson
Thomson discovered the electron during an experiment testing cathode rays, in 1897. Then he went on to create an updated version of the atomic model. -
Max Planck
He created a Quantum Theory for Quantum Mechanics. He also did a lot of work with light, energy, and radiation. He published his work in a paper. This contributed to a better version of the atomic model, with orbits of the electrons in the electron cloud. -
Ernest Rutherford
discovered the concept of radioactive half-life, proved that radioactivity involved the nuclear transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation
nuclear structure of the atom and the essential nature of radioactive decay as a nuclear process
using natural alpha particles, demonstrated induced nuclear transmutation, and later, using protons from an accelerator -
Niels Bohr
Bohr’s research led him on to theorize in a series of articles that atoms give off electromagnetic radiation due to electrons jumping to different orbit levels. Bohr’s work changed the original beliefs that were based off of Ernest Rutherford’s work. His work would later be modified by other scientists, but mostly still stands today. -
Henry Moseley
The increase in the number of neutrons per successive element was not so exact
hydrogen has no neutrons whereas its two-proton successor helium has two neutrons
next element lithium has three protons but four neutrons which is two more neutrons than its predecessor
X-ray spectrometers -
Robert Millikan
oil-drop experiment in which he measured the charge on a single electron. J.J. Thomson had already discovered the charge-to-mass ratio of the electron
Millikan and his then graduate student Harvey Fletcher used the oil-drop experiment to measure the charge of the electron and electron mass -
Erwin Schrodinger
Schrodinger changed the Quantum theory by coming up with a new wave equation for electron movements. The equation can accurately calculate the energy levels in atoms. This has been called one of the most important discoveries of the 20th century. He is also known for his studies of color and colorimetry. -
Werner Heisenberg
German physicist
Seminal paper published in september 1925
In early 1929, Heisenberg and Pauli submitted the first of two papers laying the foundation for relativistic quantum field theory. -
James Chadwick
James Chadwick was the person who discovered the neutron. He also discovered that electrons are not inside the nucleus they are only on the outside, and protons and neutrons are inside the nucleus. He also proved that the neutron has the same mass as a proton, and that it has a neutral charge.
