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460
Democritus
Democritus thought of the idea of atoms. He started questioning the structure of matter, posing the question, what would happen if continued to break a piece of matter, until it couldn’t be broken any further. He proposed that after you break every single piece to its extent, all that’s left are single basic matter particles, which were atoms. -
Period: 460 to
The Development of Information about the Atom
Note: The discovery made by Democritus is 460 B.C, not 460 A.D. -
Period: 500 to
Lack of development of information about the atom
For over 2000 years, no more work was done on the structure of matter and the atom. -
Lavoisier
Antoine Lavoisier discovered fixed air, which he later named oxygen. From the experimentation, which occurred while discovering oxygen, the combustion theory was created. Other chemists followed his idea that an element was a singular form, which could not be broken down any more. This was important in John Dalton’s achievement. -
John Dalton
John Dalton states his atomic theory at a Royal Institution. This theory included ideas such as:
• All matter is composed of atoms
• Atoms cannot be made or destroyed
• All atoms of the same element are identical
• Different elements have different types of atoms chemical reactions occur when atoms are rearranged
• Compounds are formed from atoms of the constituent elements.
This then led to the early formation of the Periodic Table when he united his atomic theory of matter with the concept of -
J.J. Thomson
J.J. Thomson discovered the electron. This was discovered after a series of experiments were designed with the intention to study the nature of electrical discharge in a high-vacuum cathode-ray tube. He discovered electrons when the rays that he was experimenting with were deflected by electrically charged plates and magnets. He suggested that “bodies much smaller than atoms” were the cause. He then proposed a new structure of the atom, including electrons, both positive and negative. -
Max Planck
Radiation was brought to the attention of Planck in 1900, and he was able to prove that these were electromagnetic in nature. He studied the distribution of energy through radiation. Through experimental observation, he found that radiation had defied previous information about physics. This interested him further. In 1900, he published a paper, which discussed the relationship between energy and radiation frequencies. He showed that when you vibrate atoms to a certain extent, you can measure th -
ALBERT EINSTEIN!
Albert Einstein formulated his theory of relativity. In 1905, Einstein presented his paper, “The Electrodynamics of Moving Bodies,” in which he presented the previously unimaginable theory. In this paper, he was able to explain that light absorption can release electrons from atoms, a reaction called the “photoelectric effect”. -
Ernest Rutherford
Alpha rays, from the element, radium, were used by Ernest Rutherford in his attempt to investigate the inside of an atom. Alpha rays were particles which were made of the same substances as those found in an atom’s nucleus. In his experiment, Rutherford shone them onto atoms, which were inside gold foil. It was soon found, that the particles from the alpha rays, could be deflected or pass through the gold foil. Eventually, he was able to discover the protons, after he used alpha rays to take ou -
Niels Bohr
Danish scientist, Niels Bohr was famous for the theory that electrons do not spiral into the nucleus of an atom, which had occurred during Rutherford’s experimentation. He created two rules: one was that electrons are only allowed to orbit at certain distance. The other was that when an electron, jumps from a higher energy point of orbit to a lower energy point of orbit, the atoms radiate energy. This theory, was however, found to have its flaws. The model which Bohr had proposed of the atom was -
Wolfgang Pauli
Pauli made the prediction that electrons in an atom can spin in two directions when orbiting the nucleus. He had designed a model for the Bohr-Sommerfield model. This model contained information about how each electron has a set of quantum numbers, and now electron has the same amount of quantum numbers inside. This is called “Pauli’s Exclusion Principle”. -
Enrico Fermi
In 1942, Enrico Fermi conducted the first controlled chain reaction releasing energy from the atom’s nucleus. During World War II, Fermi was well known for his efforts in producing atomic energy. He was on the American side, having left Italy because his wife was Jewish. In December of that year, he was able to create the first controlled nuclear fissure chain reaction, and throughout World War II, he worked on the atomic bomb termed. “The Manhattan Project”.
