atomic theory project

Democritus- the first atomic theory

400 BCE

Democritus, a philosopher who lived from 460 BC to 370 BC, proposed the first idea of an atom around 400 BC where he referred to them as "atomos". he said that that atomos were indestructible, always in motion, and that there were an infinite number of atoms and kinds of atoms. it is worth note that although this is only philosophy, this is a very accurate depiction of the atom for Democritus's time. he also had help from his mentor Leucippus to formulate these ideas

John Dalton- Solid Sphere

1803

John Dalton was born on September 5th, 1766, and died on July 27th 1844. Dalton was the first person to dispute Democritus's ideas of atomic theory for more than 2000 years! he agreed that atoms exist however he thought they worked differently. he said that all atoms of a given element are completely identical, and that different atoms weren't. he also proposed the idea of chemical reactions causing atoms to make chemical compounds. Dalton died of a stroke

JJ Thomson- discovers the electron

1897

JJ Thomson was born on December 18th, 1856 and died on August 30th, 1940. In the 1890s Thomson was experimenting with charged particles in gases. In 1897. he demonstrated that cathode rays were made out of particles that conduct electricity, which we know today as the electron. Thomas stated that these electrons were part of the atom. it is worth noting that his only son also won the Nobel prize in 1937.

Robert Millikan- the Charge of the Electron

1910

Robert Millikan was born on March 22nd, 1868 and died on December 19th, 1953. Robert was the first man to determine the magnitude of the electron's charge in 1910. in his experiment small electrically charged drops of oil were held up between two metal plates, and the downward force of gravity and the upward attraction of an electrical field suspended them. Robert was able to then measure how the various drops of oil moved and show that their charge was always a multiple of the electrons charge.

Ernest Rutherford- the Planetary Model

1911

Ernest Rutherford was born on August 30th, 1871, and died on October 19th, 1937. Ernest was a previously known scientist for his work with radiation but also well-known is his atomic theory. he came up with this theory after an experiment where he shot positively charged alpha particles a thin piece of gold foil. his theory stated that the atom had a small positively charged nucleus where the mass is concentrated. he also said that there were negatively charged electrons circling the nucleus.

Niels Bohr- the Planetary Model

1913

Niels Bohr was born on October 7th, 1885, and died on November 18th, 1962. Niels, in 1913, proposed an idea about the structure of the atom based off of previous works and his knowledge of quantum theory. his theory stated that some physical quantities only took discrete values. he also said that electrons only move around the nucleus in prescribed orbits and that when electrons jump from orbit to orbit, they emit radiation. Niels had spent time working with both Rutherford and Thomson.

Erwin Schrodinger- The Wave Equation

1926

Erwin Schrödinger was born on august 12th, 1887, and died on January 4th, 1961. Erwin was known for a lot of his venture in the scientific world, one of his most important ones being the wave equation. this equation was formed in 1926 and was used to accurately calculate the energy levels of electrons in atoms. this also added another layer to the atomic model, known as the quantum mechanical model of the atom. Erwin was also famous for Schrödinger's cat which today is well known in the media.

Werner Heisenberg- The Uncertainty Relation

1927

Werner Heisenberg was born on December 5th, 1901 and died on February 1st, 1976. in 1927 Heisenberg was conducting an experiment in which he was trying to measure the position of an electron with a gamma ray microscope, however the microscope's high-energy photons would move the electrons in an uncertain way. and better microscopes only moved the electrons more. The more precisely you try to measure the position, the more uncertain the momentum became. this was known as the uncertainty relation

James Chadwick- Discovering the Neutron

1932

James Chadwick was born on October 20th, 1891, and died on July 24th, 1974. in 1930 Herbet Becker and Walter Bothe shot alpha particles at beryllium which caused a strong radiation to occur. the reason for this was unknown although it was speculated that it could be high-energy electromagnetic radiation. However, in 1932 James Chadwick proved that the radiation was caused by a neutral particle with about the same mass as a proton, which could be found in the nuclei. thus, the neutron was born.