History of Atomic Theory

Democritus

460

At around 460 B.C., Democritus developed the idea of atoms. His theory states that no specific size that can be recognized to the various atoms and can vary depending on different factors manipulating them. He began the experiment to show the number of breaks you need to make before you cannot break it any further. His indication was that it would end at some point by a smallest possible bit of matter which he called atoms. As a result, the influential Aristotle did not support his idea.

John Dalton

Oct 9, 1800

Dalton performed experiments with various chemicals that showed that matter consisted of particles that are now known to be atoms. The findings of the experiment showed that every matter is made up of particles, atoms. Due to his findings, he hypothesized that all matter is made up of atoms, and they are inseparable and durable. He also stated that all atoms of a certain element are equal in mass and properties.

J.J. Thomson

Dec 12, 1897

Thomson first suggested that atom was made up of electrons fixed onto a cloud of positive particles. His experiment was bending a ray of Cathode Rays using a set of negatively and positively charged plates. The he observed that the cathode rays were going towards the positively charged plates, which means that the ray was negatively charged. Thomson then called the negatively charged particles in the ray, electrons.

Max Planck

Dec 15, 1900

Planck proposed the quantum of action, which explains the pattern of lights concentration released from a black body at any frequency given. His experiment showed what would happen when movement between atoms occurs. Planck clarified that energy is not a constant unit, but is carried in small irregular units. He named the energy caused by the moving atoms, quanta. The conclusion he made seemed mysterious to some scientists, but offered a new understanding of the structure of light and radiation.

Robert Millikan

Oct 10, 1906

Millikan used the Millikan oil-drop experiment to establish the charge of an electron. He used single drops of water which he waited for it to evaporate and then added oil. Even though his measurement included 0.5% of error due to incorrect value for thickness of air. He also stressed upon the fact that his data proved false to some scientists who said that electrons were not original and isolated. Millikan also presented a value for the electronic charge which gave an accurate rydberg constant

Ernest Rutherford

Oct 12, 1911

Rutherfords experiment was to bombard atoms with alpha rays to observe the inside of an atom. The experiment he made was firing radioactive particles through gold foil while detecting them by fluorescent screen.This lead him to conclude that most of the atom was made up of empty space.

Arnold Sommerfeld

Oct 10, 1920

With the help of Bohr, Sommerfeld expanded the Bohr model to clarify the troubles that were present in the original model, which is that of Bohr's atom being too simple to explain the heavier elements. With further trials, they found out that the electrons do not only travel in particular orbits, but can have a variety of shapes, which can tilt in the existence of a magnetic field.

Wolfgang Pauli

Aug 13, 1924

Pauli contributed by laying the foundations of quantum theory of fields. He showed that a fourth quantum number named spin quantum number was mandatory to explain the state of an atomic electron. In addition, he had a principle that states two electrons cannot exist in an atom, in the same state, with the same quantum numbers. This helped him give a clear description of electron distribution having various atomic energy states using quantum.

Werner Heisenberg

Oct 10, 1925

Heisenberg had a theory called matrix mechanics that clarified the performance of the atom. To prove his theory, he backed it up with mathematical quantities known as matrices that can be related to the idea of electrons as particles, similar to Schrodingers theory, but he backed his theory up using waves yet both of them were mathematically equal.

Erwin Schrodinger

Dec 30, 1926

Bohrs experiment was to form a model of the atom using particle waves. Although he might not have come up with a clear conclusion as it is difficult to form a reliable model of an atom, the result of his experiment showed that the vibrations traveled in circles. He also used a psi symbol, from the Greek lettering system, to name the wave mechanics.

James Chadwick

Oct 10, 1932

Chadwick created an experiment that included the bombing of beryllium with a particle to produce radial, which is then used to bomb hydrogen and nitrogen. This produced a hydrogen nuclear and nitrogen nuclear. As a conclusion, he said that it was not radial, as radial has no momentum to produce a proton in the atom. He then believed that the outcome from the beryllium was a neutral particle that has a similar mass to proton, which he found out that it was a neutron as it had not electric charge

Hideki Yukawa

Oct 10, 1935

Yukawa's theory was that exchange forces can describe the strong force between nucleons. Nonetheless, virtual, or real, photons did not have the required strength for this force, which then lead him to think that there has to be another kind of a virtual particle. He then decided to use Heisenberg's uncertainty to clarify that a virtual particle can exist for a small fraction of a second. With uncertainty, it helped particles (250 times heavier than electron), to exist strongly at certain times.