History of Chemistry

Dalton's Atomic Theory

Jan 1, 1803

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. Info-http://www.rsc.org.Picture-www.google.com/search.

Cathode rays

Jan 1, 1879

William Crookes made headway in modern atomic theory when he used the vacuum tube made by Heinrich Geissler to discover cathode rays.When electricity was run through the apparatus, an image of the cross appeared and the zinc sulfide glowed.Info-www.columbia.edu. picture-www.google.com/search

Proton

Jan 1, 1885

Eugene Goldstein discovered positive particles by using a tube filled with hydrogen gas (this tube was similar to Thomson's tube...see 1897). The positive particle had a charge equal and opposite to the electron. It also had a mass of 1.66E-24 grams or one atomic mass unit. The positive particle was named the proton.Info-www.columbia.edu. picture-www.google.com/search

x-rays

Jan 1, 1895

Wilhem Roentgen accidentally discovered x-rays while researching the glow produced by cathode rays. He discovered that the rays that were causing the fluorescence could also pass through glass, cardboard and walls. The rays were called x-rays.Info-www.columbia.edu. picture-www.google.com/search

mass of an electron

Jan 1, 1897

Robert Milikin discovered the mass of an electron by introducing charged oil droplets into an electrically charged field. Millikan found the mass of one electron to be 9.11E-28 grams and its charge to be 1.602E-19 coulombs.Info-www.columbia.edu. picture-www.google.com/search

J.J Thomson and the electron

Jan 1, 1897

J.JThomson found that the cathode rays were negatively charged and that each charge had a mass ratio of 1.759E8 coulombs per gram. He concluded that all atoms have this negative charge (through more experiments) and he renamed the cathode rays electrons. His model of the atom showed a sphere of positively charged material with negative electrons stuck in it.Info- www.columbia.edu. Picture- www.google.com/search.

Ernest Rutherford

Jan 1, 1911

Ernest Rutherford sent a radioactive source through a magnetic field. Some of the radioactivity was deflected to the positive plate; some of it was deflected to the negative plate; and the rest went through the magnetic field without deflection. Thus, there were three types of radioactivity: alpha particles (+), beta particles (-) and gamma rays (neutral). Info-ww.columbia.edu. Picture-ww.google.com/search

Niel Bohr- atomic model

Jan 1, 1915

Model is an approximation to quantum mechanics that has the virtue of being much simpler. In the Bohr Model the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. Info-http://csep10.phys.utk.edu. Picture-http://csep10.phys.utk.edu.

Nuetron bombardment and nuclear Fission

Jan 1, 1932

Enrico Fermi bombards elements with neutrons and produces elements of the next highest atomic number. Nuclear fission occurred when Fermi bombarded uranium with neutrons. Info-www.columbia.edu. picture-www.google.com/search