-
In 400 BC, Democritus proposed and created the first atomic model. It was simply a round sphere with no electrons, protons, or neutrons. His contribution helped people with understanding the idea of an atom, and helped other scientists further look into the science of the atom and its generic makeup.
-
Portrait of Democritus in 400 B.C.
-
Portrait of Antoine Lavosier in 1774.
-
Antoine Lavosier began carefully study of the burning process. He proposed the Combustion Theory which was based on sound mass measurements. He named oxygen. He also proposed the Law of Conversation of Mass-stating that matter would be conserved throughout any type of reaction- which represents the beginning of modern chemistry.
-
John Dalton created the first true model of the atom. Also, he stated that chemicals were composed of atoms and that only whole number of atoms can combine to form compounds. He developed the Atomic Theory of Matter, which most importantly stated that all mater is composed of atoms, atoms of a given element are identical in size and mass, and lastly, atoms cannot be subdivided, created, nor destroy, which we now know is wrong.
-
Portrait of John Dalton in 1808.
-
Henri Becquerel is most widely famous and known for the discovery of radioactivity. He left a rock and a wrapped photographic plate in his desk drawer and found later that the plate, though unexposed to light, had developed patterns which would ordinarily indicate exposure. Becquerel was also the professor of Marie Curie who went on to further explore his theories.
-
Becquerel Picture of Henri Becquerel in 1896. For more information on Becqurel, click on the link
-
Thomson thought that the atom was mostly positive matter with negative matter sprinkled throughout. He made an analogy comparing the atom to plum pudding, where the postive matter was the pudding and the negative matter was the plum. Basically, Thomson discovered the electron in 1897.
-
Thomson Photograph of J.J. Thomson in 1897. For more information on Thomson, click on the link.
-
Planck Photograph of Max Planck in 1899. For more information on Planck, click on the link.
-
More About Max PlanckIn 1899, Max Planck, a German physicist, explained that energy is not a continuous, flowing entity, but is carried in tiny units, which he named quanta and described as "the pennies of the atomic world". Each quantum's energy is "equal to the frequency of radiation multiplied by the universal constant" which Planck also defined. His Quantum Theory won him the Nobel Price for physics in 1918
-
The Curie's in 1903.
-
Curie took Becquerel's work a few steps further, conducting her own experiments on uranium rays. She discovered that the rays remained constant, no matter the condition or form of the uranium. The rays, she theorized, came from the element's atomic structure. This revolutionary idea created the field of atomic physics and Curie herself called it radioactivity when describing the phenomena. Becquerel and the Curies shared the Nobel Prize in Physics in 1903.
-
After testing his oil-drop experiment, Robert Millikan, an American physicist, accurately determined the charge of an electron and also the mass of an electron. Millikan's later experiments had notable impacts on the later research efforts of James Bohr and Albert Einstein.In 1923 he was awarded a Nobel Prize in physics for both his work in determining the charge on the electron and exploring the photoelectric effect.
-
Millikan For more information on Robert Millikan, click on the link.
-
Rutherford was J.J. Thomson's student. He conducted an experiment where a narrow beam of alpha particles were shot/aimed at a thing sheet of gold foil. After doing so, he concluded that all postive charge is concentrated in the small core in the center of the atom (nucleus) and that all the mass of the atom was also concentrated in the nucleus. The atom was mostly empty with negative particles surrounding it.
-
Rutherford For more information on Ernest Rutherford, click on the link.
-
Bohr For more information on Niels Bohr, click on the link.
-
Mosely For more information on Henry Mosely, click on the link.
-
Niels Borh was a Danish physicist that was one of Ernest Rutherford's student. Bohr's atomic theory stated that electrons could only occupy certain shells or orbits in an atom, and each orbit represents a definite energy for the electrons in it. For testing this with a hydrogen atom, and being proved correct, he got the Nobel Prixe in Physics 9 years later. The importance of Bohr's revolutionary discovery has been referred to as 'the greatest discovery in physics' by many.
-
In 1913, Henry Mosely discovered that the energy of x-rays given off by the elements increased in a linear with each successive element in the periodic table. Then also in 1913, he proposed that the relationship was a function of the positive charge on the nucleus, meaning the protons. This rearranged the periodic table by using the atomic number instead of atomic mass to represent the progression of the elements. This new table left additional holes for elements that would soon be discovered.
-
Werner Heisenber was a German physicist and philosopher who discovered a way to "formulate quantum mechanics in terms of matrices." For that discovery, he was awarded the Nobel Prize for Physics for 1932. He also made some contributions to the atomic nucleus and subatomic particles.
-
HeisenbergFor more information on Heisenberg, click on the link.
-
In 1926, Erwin Schrodinger, an Austrian physicist, took Bohr's simple model a step further and using mathematical calculations calculated the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model. This model predicted the odds of the location of the model. Basically, this model introduced the idea of subenergy levels.
-
Schrodinger For more information on Erwin Shcrodinger, click on the link.
-
Chadwick For more information on James Chadwick, click on the link.
-
In 1932, British physicist James discovered the neutron. He also established the idea that the atomic number of an element is the number of protons it has. Chadwick then got the Nobel Price of Physics for his discovery of neutrons in 1935. Chadwick also took a large part in the Manhattan Project, trying to develop the atomic bomb while in England.
-
Aristotle did not believe in the atomic theory. He thought that all materials on Earth were not made of atoms, instead of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. Most people followed Aristotle’s idea, causing Democritus’ idea- which was that all substances on Earth where made of small particles called atoms- to be over looked. Aristotle's view was later proven incorrect.
-
Sculpture of Aristotle in 384 B.C.
