-
Period: 492 BCE to 432 BCE
Empedocles
Empedocles devised the theory that all matters are made of four pure substances that cannot be destructed- air, fire, water, and earth -
400 BCE
Democirtus
Democritus first raised the idea of atomic theory- all matters are made of small discrete particles. Democritus called them "atomos". These small particles are physically indivisible but geometrically divisible in his theory -
Alchemists
Alchemy is a branch of natural philosophy when originated in Greco-Roman Egypt. The alchemy is the very start of chemistry where alchemists try to purify and mature materials, the goal was to turn base metal into noble metals like gold. -
Dalton
John Dalton proposed the idea that all matters are made of indestructible and indivisible atoms. His law also has the other four statements. All atoms of an element are identical, for different elements, the atoms have different weights and properties, atoms are composed of a simple whole number, and atom cannot be created or destroyed. -
Thomson
J.J.Thomson found out electrons by using a cathode ray tube. He proposed the idea that atoms consist of both positive and negative charged particles. The model was named "plum pudding model" -
Marie Curie
Marie Sklodowska Curie after separating various materials by continuous chemical reaction and crystallization in the lab along with her husband; tested the ability to ionize with air, they discovered polonium and radium salts that had been derived from tons of uranium ore. In 1906, Marie produced a pure specimen of radium. -
Planck
Max Planck is known for the discovery of the quantum theory, he was the first to originate this theory. Planck's quantum theory describes the energy of the light is proportional to the frequency. There is also a Planck constant, we can calculate the energy of elements using Plank's quantum theory -
Nagaoka
Hantaro Nagaoka proposed an alternative planetary model of the atom in which the center of the positive charge is surrounded by many rotating electrons just like Saturn and its ring. Saturn represents a massive atomic center and rings revolving Saturn represent electrons bonded by electrostatic forces revolving the atomic center. -
Rutherford
Ernest Rutherford is known for his famous gold foil experiments which led him into discovering the nucleus in an atom. When bombarding the gold foil with beams of alpha particles, Rutherford discovered that some particles deflect away. The electrons cannot do such deflection to the alpha particles, so that means that there is another tiny, dense part in an atom. It is the nucleus. -
Bohr
Niels Bohr proposed a Bohr model to explain the spectrum of hydrogen atoms by introducing quantization conditions. He proposed the principle of complementarity and interpretation of quantum mechanics in Copenhagen. he also proposed that electrons are arranged in a circular orbit around the nucleus. -
Einstein
Albert Einstein has proved many theories. He won Nobel price for discovering the law of the photoelectric effect. Photoelectric describes the transferring of photons and electrons. He also explained the Brownian movement which describes particles move randomly in fluid because of the collision with other particles. He also is famous for the equation E=mc2 energy equals mass times the speed of light squared. -
De Broglie
Louis de Broglie developed the concept of all matter has wave properties based on light has wave-like and particle-like properties. The concept is called de Broglie hypothesis. He proposed electrons should also have wave-like properties just like light. -
Bose
Satyendra Nath Bose is known for his contribution to the quantum statistic. He derived Planck's quantum radiation law by counting states with identical particles without any reference to classical physics. Then he sent his paper to Albert Einstien which Einstein agreed with and translated into Germany. Bose has not been rewarded with any recognition (prizes) -
Pauli
Wolfgang Pauli was famous for identifying the other two quantum numbers. He stated that two electrons in an atom cannot have the same sets of quantum numbers at the same time. The two electrons of the helium atom are in the first layer. For example, the shape of the electron cloud is spherically symmetrical, and only one direction is exactly the same. The direction of the spin must be the opposite. Each track can only accommodate two electrons with opposite spins. -
Schrödinger
Erwin Schrödinger developed the Bohr model more, where to find the electrons in certain positions. The model is known as the quantum mechanical model. Not like the circular path of the Bohr model, this model has an electron cloud circling the nucleus. the denser the cloud in one area is, the more likely electrons are going to appear there. This model introduces the concept of the sub-energy level. -
Heisenberg
Werner Heisenberg contributed to the atomic theory by formulating quantum mechanics. He is best known for the Heisenberg uncertainty principle. The uncertainty principle is you can't know the position of a particle and its velocity at the same time. The uncertainty of the particle position must be greater than or equal to the Planck constant divided by 4π. It shows that the particle behavior of the micro is very different from the macro material. -
Chadwick
James Chadwick discovered the neutrons in atoms by shooting alpha particles at beryllium atoms. Unknown radiation was then produced, he interpreted this observation by seeing the radiation as being composed of particles of mass approximately equal to that of the proton but without electrical charges- neutrons -
Richard Bader
Richard F.W. Bader found that electron density is important to explain the behavior of atoms in molecules. There is no atomic orbital in the molecule according to his theory which was not accepted by the major scientists. His theory was against the accepted theory. It is hard for him to publish his work. But finally, his theory was accepted by more and more people
