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Period: 370 to 460
Democritus
The exact date of when Democritus was born or dead is not known.
Around 460 BC Democritus was born in Abdera, Greece and around 370 BC, he was dead.
Democritus was a Greek philosopher who adopted the theory of atom first time.
Interesting fact - He published more than 90 publications and was born in wealthy family.
* Since the Timetoast site does not allow me to set the date before the century, I just put the year. -
400
Democritu's Atomic Theory (3)
The atomic model of Democritus was small plain sphere with no protons, neutrons, or electrons.
People usually thinks that the concept of atom was first came up with Democritus but actually Democritus’ mentor, Leucippus, came up with Democritus. -
400
Democritus' Atomic Theory (1)
(the exact date or year of when Democritus announced his atomic theory is unknown)
Democritus believed that all things in the world is made of “atomos (later we call it atom),” and claimed that if any object is kept divided, then it will reach to the atom which cannot be divided anymore. -
400
Democritus' Atomic Theory (2)
Democritus’ Theory states…
- All matter consists of invisible particles called atoms.
- Atoms are indestructible, solid but invisible and homogenous.
- Atoms differ in size, shape, mass, position, and arrangement.
- Atoms that made up…
o solids are small and pointy
o Liquids are large and round.
o Oils are very fine and small that can easily slide pass each other. -
Period: to
Antoine Lavoisier
Born: August 26, 1743, Paris, France
Died: May 8, 1794, Place de la Concorde, Paris, France
Lavoisier was a French Chemist who is called as the father of the chemistry.
Interesting Fact
- Lavoisier was hanged during the French Revolution, since he was tax collector.
- He created the first Chemistry textbooks and tables. -
Period: to
John Dalton
Born: September 6, 1766, Eaglesfield, Cumbria, United Kingdom
Died: July 27, 1844, Manchester, United Kingdom
John Dalton was a British chemist and physicist who developed and founded the modern atomic theory.
Interesting Fact
– He won Royal Medal.
- He never married. -
Lavoisier's contribution to Atomic Theory (2)
Also he recognized and named the oxygen after doing experiment turning mercury oxide (HgO) into mercury (Hg) and oxygen (O), and discovered compounds such as diamonds, water, etc. were made up of elements. Usually those discoveries were done by combusting experiments. His works explained what exactly atom was. Moreover, quantitative measurements which he created made the compositions of compounds be determined possible with higher accuracy. -
Lavoisier's contribution to Atomic Theory (1)
(Exact Date is unknown)
Lavoisier was the French Chemist who founded several elements and put the first table of the elements together, and discovered the law of conservation which law states the matter/element as a simple substance can change the shape but cannot be broken down/destroyed nor created, mass remains equally, and elements are reacted with each other in same proportions. -
Dalton's Modern Atomic Theory (2)
John Dalton’s Atomic Theory states…
- All matter are composed of atoms
- Atoms are indivisible and cannot be destroyed
- Atoms of a given element are all same in size, mass, and chemical properties
- Atoms of specific elements and those of other elements are different.
- With a chemical reaction, atoms can be separated, combined and/or rearranged.
Dalton's Atmoic model was solid indestructible sphere.
(the exact date is unknown) -
Dalton's Modern Atomic Theory (1)
Dalton proposed atomic theory that elements were made up of small particles named atom and the atoms cannot be created nor destroyed. His theory and Democritus’ theory were different because Dalton’s theory was not just philosophical idea but had more scientific ideas and had the idea of the weight of atoms particularly. Furthermore, he developed the concept of molecule, proposed the symbol system to represent the atoms of different elements, and brought up the law of simple multiple proportion. -
Period: to
Joseph.John Thompson
Born: December 18, 1856, Manchester, United Kingdom
Died: August 30, 1940, Cambridge, United Kingdom
Joseph John Thomson was a British physicist who discovered electron in atom.
Interesting Fact
– He won the Nobel Prize in physics in 1906, as he discovered the electron -
Period: to
Max Planck
Born: April 23, 1858, Kiel, Germany
Died: October 4, 1947, Göttingen, Germany
Max Planck was a German scientist who created the Quantum Theory.
Interesting Fact
- Max Planck won the Nobel Prize in Physics in 1918. -
Period: to
Marie Curie
Born: November 7, 1867, Warsaw, Poland
Died: July 4, 1934, Passy, Haute-Savoie, France
Marie Curie and her husband Pierre Curie were the European couple who studied chemistry especially the radioactivity.
Interesting Fact
– Marie Curie won two Nobel Prizes in physics and chemistry respectively in 1903 and in 1911.
- She was the first women won the Nobel Prize.
- Her notebook is still radioactive. -
Period: to
Robert Millikan
Born: March 22, 1868, Morrison, Illinois, United States
Died: December 19, 1953, San Marino, California, United States
Robert Millikan was the American Physicist who measured the charge of an electron.
Interesting Fact
- He won the Nobel Prize in physics in 1923.
- He was also inspired by Max Planck’s Quantum Theory and later involved in. -
Period: to
Ernest Rutherford
Born: August 30, 1871, Brightwater, New Zealand
Died: October 19, 1937, Cambridge, United Kingdom
Ernest Rutherford was a British-New Zealand chemist who studied nucleus of the atom.
Interesting Fact
- The element 'Rutherfordium' was named after Rutherford’s name.
- Rutherford won Nobel Prize in Chemistry in 1908. -
Period: to
Albert Einstein
Born: March 14, 1879, Ulm, Germany
Died: April 18, 1955, Princeton, New Jersey, United States
Albert Einstein is a German theoretical physicist who developed the general theory of relativity, Quantum mechanics, and mass–energy equivalence formula.
Intersting Fact
- Einstein is known as he was bad student and failed every subject, but is is a rumour Einstein did NOT flunk math.
- Einstein won the Nobel Prize in physics, in 1921. -
Period: to
Niels Bohr
Born: October 7, 1885, Copenhagen, Denmark
Died: November 18, 1962, Copenhagen, Denmark
Niels Bohr was a Danish physicist who brought atomic model which is still used in modern days.
Interesting Fact
- Bohr wom the Nobel Prize in physics, in 1922.
- Bohr's son, Aage, also won the Nobel Peace Prize in 1975. -
Period: to
Erwin Schrodinger
Born: August 12, 1887, Vienna, Austria
Died: January 4, 1961, Vienna, Austria
Erwin Schrodinger is an Austrian scientist who studied the Quantum Theory.
Interesting Fact
- Schrodinger is well known with the Schrodinger's cat.
- Erwin Schrodinger won the Nobel Prize in physics in 1933. -
Period: to
James Chadwick
Born: October 20, 1891, Bollington, United Kingdom
Died: July 24, 1974, Cambridge, United Kingdom
James Chadwick was a British physicist who discovered neutrons in an atom.
Interesting Fact
- Chadwick won the Nobel Prize in physics in 1935.
- Chadwick were prisoned during the World War 1 -
Period: to
Louis De Broglie
Born: August 15, 1892, Dieppe, France
Died: March 19, 1987, Louveciennes, France
Louis De Broglie was a French physicist who made a great contribution to the Quantum Theory.
Interesting Fact
- Louis De Broglie won the Nobel Prize in physics in 1929
- He did not marry. -
Marie Curie's Discovery of Radium and Polonium
Curie studied radioactive substances discovering radium and polonium. She was curious why “pitchblend”, a common mineral, was radioactive while no trace of uranium was founded, since at that time, uranium was the only element discovered that has radioactivity. So she grinded the pitchblend until she get radium and polonium. She stated the radioactive materials make atoms break down spontaneously and releases subatomic particles and radiation energy. Her work proved that atom are divsivble. -
J. J. Thomson's discovery of electron (1)
J.J. Thompson discovered electron and proposed a model of structure of the atom called “Plum Pudding” model. He studied “cathode ray” with a tube that glow of beam (cathode ray) appears when high voltage current is flows through the tube and the atoms it the tube. After he did a series of experiments with the cathode ray in tube and vacuum, he interpreted the data that the atom is consisted with smaller tiny particles and he called these particles as “corpuscles” nowadays we call it electron. -
J.J. Thomson's Discovery of electron/Plum Pudding Model (2)
J.J. Thomson believed that the matter filling most of the atom is positively charged and electron that is stuck/embedded on the matter are negatively charged
(the exact date is unknown). -
Rutherford's Study on the Types of Radiation
Around 1900s, Rutherford studied the types of radiation and concluded that an alpha particle (α=He^+2) was positive, a Beta particle (β=e-) was negative and a neutral particle (ϒ) was light. (the exact date is unknown) -
Max Planck's Quantum Theory
In 1900, Max Planck stated that the energy is given off in small packets of energy called photons and the energy is radiated in small, discrete units named quanta by him in the Quantum Theory. The theory had important contribution in the atom model, since it was related deeply with the energy levels in atoms.
(the exact date is unknown) -
Period: to
Werner Heisenberg
Born: December 5, 1901, Würzburg, Germany
Died: February 1, 1976, Munich, Germany
Werner Heisenberg was a German physicist who proposed the theory of matrix mechanics and'uncertainty principle.
Interesting Fact
- Werner Heisenberg won the Nobel Prize in Physics in 1932. -
J.J. Thomson - ion/rays
In 1906, J.J. Thomson started to study positively charged ions/rays.
(the exact date is unknown) -
Millikan's Oil-drop Experiment
Between 1908 and 1917, with Millikan oil-drop experiment, Millikan measured the electric charge of one single electron in the atom. Millikan wanted to prove J.J. Thomson’s statement that an electron was 1000 times smaller than an atom and validated Thomson’s hypothesis with his experiment. -
Rutherford's Gold-Foil Experiment
In 1909, Rutherford did an experiment called Gold-foil experiment and get unexpected data which denies J.J. Thomson’s plum pudding atomic model. Therefore, between 1911~1918, he created new atomic model based on his experiment result which has positively charged nucleus in the core of atom surrounded with negatively charged electron and remainder is empty. Also, he predicted the neutrons in the atom. -
Rutherford's new Atomic Model
Between 1911 and 1918, Rutherford created new Atomic Model which has...
• a very small positively charged nucleus containing most of the mass of the atom
• a very large volume around the nucleus in which electrons move
• a nucleus containing positively charged protons
• a number of protons equal to the number of electrons
(The exate date is unknown) -
J.J. Thomson's discovery on neon and isotopes
In 1912, J.J. Thomson discovered that neon was composed of two different atoms and proved the existence of isotopes in a stable element.
(the exact date is unknown) -
Niels Bohr's Proposal of "Planetary" model (1)
Bohr decided to create new atmoic model based on Rutherford's model but has differet point in orbit of the electron. Also, he made energy levels (shells) in the aton that only particular amount of electrons can fit on an energy level of an atom. -
Niels Bohr's Proposal of "Planetary" model
Bohr's Atomic model has...
- Electrons move around the nucleus in fixed orbits (like planets around the sun).
- An electron in a particular orbit has constant energy.
- An electron absorbed energy move to a higher energy orbit of larger radius. (excited electrons)
- An excited electron can fall back to its original orbit by emitting energy as radiation.
- Electrons can only exist in certain discrete energy levels. -
Einstein's Theory of Relativity and Photoelectric Effect
Einstein brought up with the theory of relativity which was basic theory to explain the release of atomic energy, and explained that the electron can be release by the light absorption from atom which is a phenomenon named the “photoelectric effect.” Since he was “theoretical” physicist, he proved the theory with calculation rather than doing experiment to prove his theory. -
Louis De Broglie's Standing Wave of Electron
Louis De Brogile stated that the electrons have properties of as waves and particle and the electron moves makeing waves not a straight line. -
Louis De Broglie
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Werner Heisenberg's Matrix Mechanic Theory
Werner Heisenberg proposed hiss Matrix Mechanic Theory which explained the property/behaviour of the atoms. -
Schrodinger's Wave-mechanics
Schrodinger proposed that the waves can be used to describe the electonrs in atoms and energy level in Bohr model with mathematical proving. -
Werner Heisenberg' Idea on Quantum Theory
Heisenberg proposed an idea called "Heisenberg uncertainty principle" that any experiment cannot measure the position and momentum of a quantum particle simultaneously. -
James Chadwick's Discovery of Neutron
Chadwick discovered neutrons in the nucleus of an atom which is electricall neutral particles and have a mass similar to the mass of a proton. By bombarding the Beryllium atom with alpha particle, Chadwick discovered the neutral particles in the nucleus.
