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Period: 470 BCE to
Atomic Structure Evolution
A timeline of the important scientists and their discoveries that aided in figuring out the atomic structure and understanding the atom -
460 BCE
Democritus (460—370 B.C.E.)
Democritus was born in Abdera, Greece in 460BC. He lived to be 90 years old, dying in the year 370 BC. He studied natural philosophy in Thrace, Athens, and Abdera, Greece. Democritus expanded the atomic theory of Leucippus, his mentor and helped jump start knowledge of the atomic structure. He enjoyed studying geometry as well, traveled to many places some of which including India, Egypt, Ethiopia, Persia, and Babylon. Democritus was never married. He was known as the "The Laughing Philosopher” -
430 BCE
Democritus cont.
Democritus atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move."
1.All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogeneous.
5. Atoms differ in size, shape, mass, position, and arrangement.
Solids are made of small, pointy atoms.
Liquids are made of large, round atoms.
Oils are made of very fine, small atoms that slip past each other. -
Antoine Lavoisier (1743-1794)
Antoine-Laurent Lavoisier was born into a privileged family on August 26, 1743 in Paris, France. When he was 5, his mom left him a large sum of money when she died. Although he was attracted to the sciences, he enrolled in law school at 18, While studying for his law degree he maintained his interest in science. In 1764, the year he obtained his license to practice law and published his first scientific paper. He read a paper to the elite French Academy of Sciences and was elected to it in 1769. -
John Dalton (1766-1844)
John Dalton was born on September 6, 1766 into a modest Quaker family in Cumberland, England, and for most of his life he earned his living as a teacher and public lecturer. After teaching for 10 years at a Quaker boarding school in Kendal, he moved on to a teaching position in the burgeoning city of Manchester. There he joined the Manchester Literary and Philosophical Society, which provided him with a stimulating intellectual environment and laboratory facilities. -
Antoine Lavoisier cont.
Lavoisier was beheaded for false speculations against him. In his lifetime, Lavoisier announced a new fundamental law of nature: the law of conservation of mass: matter is conserved in chemical reactions or stated in another way and the total mass of a chemical reaction’s products is identical to the total mass of the starting materials. The law of mass conservation only became firmly established after he discovered it, he identified carbon, oxygen and sulfur to be elements. -
John Dalton cont.
He proposed the Law of Multiple Proportions, which led to the proposal of the Atomic Theory in 1803. He also developed the concept of the mole and proposed a system of symbols to represent atoms of different elements. Dalton recognized the existence of atoms of elements and that compounds formed from atoms. He came up with a formula for water of HO. He then assigned a atomic weight of one to hydrogen and developed a atomic weight scale. He also discovered color blindness, which he suffered. -
John Dalton cont.
Dalton's Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.
Dalton proposed that all matter is made of tiny indivisible particles called atoms, "solid, massy, hard, impenetrable, movable particles". -
Joseph John Thomson (1856-1940)
J.J. Thomson was born on December 18, 1856, in Cheetham Hill, England, and went on to attend Trinity College at Cambridge, where he would come to head the Cavendish Laboratory. His research in cathode rays led to the discovery of the electron, and he pursued further innovations in atomic structure exploration. Thomson won the 1906 Nobel Prize in Physics, among many other accolades. He died on August 30, 1940. -
Max Planck (1858-1947)
Max Karl Ernst Ludwig Planck was born in Kiel, Germany, on April 23, 1858. Planck studied at the Universities of Munich & Berlin, and received his doctorate of philosophy at Munich in 1879. He was Privatdozent in Munich from 1880 to 1885, then Associate Professor of Theoretical Physics at Kiel until 1889, in which year he succeeded Kirchhoff as Professor at Berlin University, where he remained until his retirement in 1926. He died at Göttingen on October 4, 1947. -
Marie Curie (1867-1934)
Born Maria Sklodowska on November 7, 1867, in Warsaw, Poland, Marie Curie became the first woman to win a Nobel Prize and the only woman to win the award in two different fields (physics and chemistry). She died on July 4, 1934. -
Robert Millikan (1868-1953)
Robert A. Millikan was born March 22nd, 1868 in Morrison, Illinois. He was honoured with the Nobel Prize for Physics for his study of the elementary electronic charge & the photoelectric effect. Millikan graduated from Oberlin College and obtained his doctorate at Columbia University. He became an assistant at the University of Chicago, where he became a full professor. In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron. -
Ernest Rutherford (1871-1937)
Ernest Rutherford was born on August 30, 1871, in Nelson, New Zealand, the fourth child and second son in a family of seven sons and five daughters. He was president of both the Royal Society and the Academic Assistance Council. -
Albert Einstein (1879-1955)
Albert Einstein was born on March 14, 1879, in Ulm, Württemberg, Germany & died April 18, 1955, in Princeton, New Jersey. He had speech difficulty & could not speak until he was 4. After public school in Munich & Aarau, Switzerland, he studied mathematics and physics at the Swiss Polytechnic Institute in Zurich. He worked as an examiner at the Swiss Patent Office in Bern, Switzerland. He continued his discussions on scientific matters with colleagues including his first wife Mileva Maric. -
Niels Bohr (1885-1962)
Niels Henrik David Bohr was born in Copenhagen on October 7, 1885, as the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife was Ellen, née Adler. Niels played soccer and was on the college team, he did really well but not as well as his brother. He died November 18th 1962, in Copenhagen, Denmark. -
Erwin Schrodinger (1887-1961)
Erwin Schrödinger was born on August 12, 1887, in Vienna, Australia, the only child of Rudolf Schrödinger, who was married to a daughter of Alexander Bauer, is Professor of Chemistry at the Technical College of Vienna. He wrote his famous thesis while recovering from tuberculosis in a sanatorium in Arosa. He died January 4, 1961. -
James Chadwick (1891-1974)
James Chadwick born October 20, 1891, Manchester, England; died July 24, 1974, Cambridge, Cambridgeshire, received the Nobel Prize for Physics for the discovery of the neutron. Chadwick was educated at the University of Manchester, where he worked under Rutherford & earned a master’s degree. After the war ended, Chadwick returned to England to study under Rutherford, he received a doctorate and he was appointed assistant director of research at the Cavendish Laboratory, Cambridge. -
Louis De Broglie (1892-1987)
Louis de Broglie was born in Dieppe, France on 15th August, 1892 and died on March 19, 1987 at 95 years old. He was a Professor of the Faculty of Sciences at Paris University, a member of the French Academy, and a Permanent Secretary of the Academy of Sciences. Broglie studied at the Lycée Janson of Sailly. Before studying, he got a degree in history, and then in science three years later. He won the Nobel Prize for Physics in 1929. -
Joseph John Thomson cont.
He identified the electron in the cathode ray tube in 1897 & deduced that the electron was a component of all matter and calculated the charge to mass ratio for the electron. e/m = -1.76 x 108 coulombs/g . He proposed the "plum pudding" model of the atom. In this model, the volume of the atom is composed primarily of the more massive positive portion. The smaller electrons are dispersed throughout the positive mass to maintain charge neutrality. Found canal rays were associated with proton H +. -
Marie Curie cont.
Curie with her husband Pierre Curie, In 1898, announced the discovery of two new elements, radium and polonium and, after Pierre's death, the further development of X-rays. -
Werner Heisenberg (1901-1976)
He was born in December 1901 in Germany, into an upper-middle-class academic family. He died in 1976. In 1920 he attened University of Munih, published 4 physics papers within 2 years. He earned his doctorate in 1923. After receiving his doctorate, he worked as an assistant to Max Born at Göttingen, then spent a year working with Niels Bohr at his institute in Copenhagen. He was awarded the 1932 Nobel Prize in Physics for the creation of quantum mechanics. -
Albert Einstein cont.
Einstein's Special Theory of Relativity, which laid the basis for the release of atomic energy. He established law of mass- energy equivalence E=mc². He calculated how the movement of molecules in a liquid can cause the Brownian motion. Using Max Planck’s quantum Theory he formulated the photon theory of light and explains the photoelectric effect. -
Robert Millikan cont.
He measured the course of charged water droplets in an electric field, but the experiment was not accurate enough so he obtained more precise results with his famous oil-drop experiment. He took up with similar skill the experimental verification of the equation to obtain an exact value of Planck’s constant to determine the unit charge of the electron thus allowing for the calculation of the mass of the electron and the positively charged atoms: e = 1.60 x 10-19 coulombs -
Niels Bohr cont.
He made huge contributions to understanding the structure of atoms & to the early development of quantum mechanics. He developed the Bohr model of the atom. In 1913, he proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Bohr's theory could explain why atoms emitted light in fixed wavelengths. He also found that an atom would not emit radiation while it was in one of its stable states, only in its transition states. -
Max Planck cont.
He is best known as the originator of the quantum theory of energy. His work contributed significantly to the understanding of atomic and subatomic processes. His work contributed significantly to the understanding of atomic and subatomic processes. Planck was able to deduce the relationship between the energy and the frequency of radiation. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant. -
Ernest Rutherford cont.
Rutherford found that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. Although positive particles had been discussed for some time, it was Rutherford in 1920 that first referred to the hydrogen nucleus as a proton. Also in 1920, Rutherford proposed the existence of the third atomic particle, the neutron. -
Louis De Broglie cont.
He created an thesis that contained important findings which he had obtained in a course of about two years. His ideas were a basis for developing the wave mechanics theory. This theory has greatly improved our knowledge of the physical nature on the atomic scale. He discovered that electrons can act like waves which helped explain some of the things electrons do that we had never been able to explain before. -
Werner Heisenberg cont.
Werner Heisenberg contributed to the atomic theory by including quantum mechanics, the branch of mechanics, based on quantum theory, used for interpreting the behavior of elementary particles and atoms. Werner's contribution to the atomic theory was that he calculated the behavior of electrons, and subatomic particles that also make up an atom. Instead of focusing mainly on scientific terms, this idea brought mathematics more into understanding the patterns of an atom's electrons. -
Erwin Schrödinger cont.
He combined the equations for the behavior of waves with the de Broglie equation to generate a model for the distribution of electrons. The Schrödinger model assumes that the electron is a wave, it describes the probability that an electron can be found in a given region of space at a given time. The only information that was important was the size of the orbit, which was described by the n quantum number. Schrödinger's model allowed the electron to occupy three-dimensional space. -
James Chadwick cont.
In 1932 Chadwick observed that beryllium, when exposed to bombardment by alpha particles, released an unknown radiation that in turn ejected protons from the nuclei of various substances. Chadwick interpreted that radiation as being composed of particles of mass approximately equal to that of the proton but without electrical charge—neutrons. -
James Chadwick cont.
In 1935 Chadwick was appointed to a chair in physics at the University of Liverpool. In 1940 he was part of the MAUD Committee, which was to assess the feasibility of the atomic bomb. The committee concluded in 1941 that the 1940 memorandum of Otto Frisch and Rudolf Peierls was correct and that a critical mass of only about 10 kilograms of uranium-235 was needed. Chadwick's discovery of the neutron led directly to the discovery of fission and ultimately to the atomic bomb.
