History Of The Atom Timeline Project

Gina Antolino

Democritus 460 BC

He had theories that atoms existed and that they were everlasting and undividable. Such speculations did not rely on experimental observation or even the scientific method. This Atomic theory also states that there's no specific size for the atoms and they differ depending on factors they encounter.

http://www.quotecollection.com/author-images/democritus-3.jpg

http://democritusatomictheory.com/

John Dalton 1803Developed a useful atomic theory of matter and concluded that an independent gas, evaporated water, exists in the air. Dalton experimented with mixing water and air particles and found that it could be seen as evaporation. Also he hypothesized that the particles that make up different gases must have dissimilar sizes.

http://en.citizendium.org/images/0/0b/JOHN_DALTON_REICH-CHEMMISTRY.jpghttp://antoine.frostburg.edu/chem/senese

/101/atoms/dalton.shtml

Mendeleev 1869Dmitri Mendeleev was a chemist and the inventor of the first version of the periodic table of elements. He found that the elements chemical properties shows trends when put in increasing order by their atomic mass.

http://www.bluffton.edu/~bergerd/nsc_111/images/Mendeleev.gif

http://chemistry.about.com/od/famouschemists/p/mendeleevbio.htm

Eugene Goldstein 1885

He discovered positive particles, known as the proton. He did this with hydrogen gas inside of a tube. The proton had a charge both opposite and equal to the electron and one atomic mass unit.

http://edu.glogster.com/media/5/25/53/52/25535237.gif

http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html

Henri Becquerel 1896Henri Becquerel studied pitchblend and its properties. When doing this he came across one of its properties involving fluorescents. He found that that the pitchblend gave off a fluorescent light with or with out the presence of sun light.

http://www.nndb.com/people/608/000072392/becquerel6-sized.jpg

http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html

J.J. Thomson 1897

J.J. Thomson is the founder of the electron. He experimented with the cathode ray and put it in a magnetic field. After doing so, he discovered that it was negatively charged and came to the conclusion that all atoms where negatively charged.

http://www.wired.com/images/article/full/2008/04/jj_thompson_400px.jpg

http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html

Ernest Rutherford 1907

Ernest founded the three types of radioactivity, alpha particles (+), beta particles (-), and gamma rays (neutral). He discovered these types of radioactivity by sending a radioactive source into a magnetic field. Experiments show that some of the radioactivity went to the positive plate, some to the negative plate, and some didn’t get deflected at all and just passed through. He also concluded that electrons were outside the nucleus and that the nucleus is very tiny. http://www.chemheritage.org/Discover/Online-Resou

rces/Chemistry-in-History/Themes/Atomic-and-Nuclear-Structure/asset_upload_file198_61208_thumbnail.jpg

http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html

Millikan 1910Robert Millikan is known for the discovery of the mass of the electron. By placing charged oil drops in an electrically charged field he could find the charge of the electron. And after doing that he found the mass of one electron by using Thomson’s mass ration.

http://www.xtimeline.com/__UserPic_Large/6064/ELT200803021630362239380.JPG

http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html

Niels Bohr 1913Niels Bohr had a theory about the structure of the atom based on Rutherford’s. He continued on the theory of the nucleus being positively charged and the electrons negative around the nucleus. Bohr said that the outer orbits could hold more than the inner ones and the outer determine the atom’s properties. Also he described that atoms “emit radiation.” Electrons emit light when jump to an inner orbit from an outer one.

http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr.jpghttp://

www2.lucidcafe.com/lucidcafe/library/95oct/nbohr.html

Frederick Soddy 1913Soddy proposed the theory of the isotope of elements. He explains how the element could have more than one form. He also proved that uranium decomposed into radium. And that the decay of radium creates alpha particles that have positive charged nuclei of helium.

http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1921/soddy.jpg

http://humantouchofchemistry.com/frederick-soddy.htm

Heisenberg 1925Werner Heisenberg was the founder of quantum mechanics. He made his new theory in terms of matrix equations. He did this because mechanical quantities such as velocity and position should be symbolized by abstract mathematical structures called “matrices” instead of ordinary numbers.

http://www.marxists.org/glossary/people/h/pics/heisenbe.jpg

http://www.mphpa.org/classic/HF/Biographies%20-%20Men/heisenberg.htm

Chadwick 1932James Chadwick is known for the discovery of the neutron. By using alpha particles he found a neutral particle with the mass close to a proton.

http://www.nndb.com/people/728/000099431/james-chadwick-1-sized.jpg

http://atomictimeline.net/index.php