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Period: to
Chemists: Atomic Theory
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John Dalton
John Dalton: (1766-1844) He was an English chemist and schoolteacher. He used experimental methods to transform Democritus’s ideas on atoms into a scientific theory. He also studied the ratios in which elements combine in chemical reactions. Dalton formulated hypotheses and theories to explain his observations and this became known as Dalton’s theory.
Wilbraham, A., Matta, M., Staley, D., & Waterman, E. (2012). Pearson chemistry (Florida ed.). Boston, Massachusetts: Pearson. -
William Crookes
Sir William Crookes, a British chemist and physicist, is well known for his cathode ray studies and development of atomic physics. He studied the effects of sending an electric current through a gas in a sealed tube. Cathodes were placed at the end of the tube and the particles are called cathode rays. These particles could penetrate thin sheets of material, showing they were smaller than atoms or molecules "Development of the Atomic Theory." Development of the Atomic Theory. Web. 3 Oct. 2015. -
Dmitri Mendeleev
Dmitri Mendeleev: (1834-1907) Mendeleev was a Russian chemist and school teacher. In 1869 he published a table of the elements. He first started his table when he was working on a textbook for chemistry classes. He arranged the element and their properties on cards, and kept moving them around until they all fit. Mendeleev made his table before scientists knew about the structure of atoms.
Wilbraham, A., Matta, M., Staley, D., & Waterman, E. (2012). Pearson chemistry (Florida ed.). Boston, -
Eugene Goldstein
Goldstein-1850-1930: In 1886 he noted that cathode rays tubes (a tube containing one or more electrons.) with a perforated cathode emit a glow from the end of the tube, near the cathode. He concluded that electrons travel from negatively charged things to positively charged things. He also noted that these rays can even pass through holes or channels in the cathode, he called them Canal Rays. Eugen Goldstein. (n.d.). Retrieved October 2, 2015. -
J.J. Thomson
J.J Thompson (1856-1940) was an English physicist who, in 1897, discovered the electron. He discovered them while performing experiments that involved passing electric currents through gasses at low pressures. In doing this he created a cathode ray, hypothesizing that it was a stream of negatively charged particles moving at high speeds. Thomson concluded that electrons are a component of all elements.
"Development of the Atomic Theory." Development of the Atomic Theory. Web. 3 Oct. 2015. -
Marie Curie
Marie Curie: (1867-1934) Curie and her husband were two of French chemist Becquerel’s associates. Curie used the word radioactivity to refer to the spontaneous emission of rays and particles from certain elements. She and her husband won the 1903 Nobel Prize in physics for their work with radioactivity. Curie also discovered the element of polonium in 1898.
Wilbraham, A., Matta, M., Staley, D., & Waterman, E. (2012). Pearson chemistry (Florida ed.). Boston, Massachusetts: Pearson. -
Robert A. Millikan
U.S. physicist Robert A. Millikan carried out experiments with a goal of finding the quantity of an electron’s charge. In order to figure this out, he conducted an oil drip experiment, to see if voltage on two plates opposite one another affected the negatively charged oil droplet’s rate of fall. By doing this experiment Millikan found the charge of each electron, then used this charge to find the mass of an electron.
"Development of the Atomic Theory." Development of the Atomic Theory. Web.2015 -
Ernest Rutherford
developement of the atomic theoryErnest Rutherford proposed that an atom is mostly empty space with a small region called the nucleus. He conducted an experiment and recorded how many particles bounced off or went through the nucleus. The particles that bounced off were the particles that hit the nucleus. The particles that went through hit the space around the nucleus. Since more particles went through than bounced off, Rutherford could conclude that the nucleus was very tiny. He created a new atomic, with electrons. -
Niels Henrik David Bohr
Bohr-1885-1962: In 1993 he proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in set orbits. Niels Bohr - Facts. (n.d.). Retrieved October 2, 2015. -
Henry Moseley
Moseley-1887-1915: In 1913 he used a self built equipment to prove that every element’s identity is uniquely determined by the number of protons it has. After this discovery he predicted four elements that he thought people would find in the future, he was correct with all four of his predictions. Henry Moseley. (n.d.). Retrieved October 2, 2015. -
James Chadwick
Chadwick-1891-1974: Chadwick discovered the neutron in 1932 and won a Nobel Prize for Physics in 1935 because of it. He also led a British team in the Manhattan Project to support the U.S.A. when they were trying to create the atomic bomb during WWII. James Chadwick. (n.d.). Retrieved October 2, 2015.
