THE HISTORY OF AN ATOM

TIMELINE

By: Angelica Mena

Democritus-460 BC

Democritus was an ancient Greek philosopher born in Greece. In his atomic hypothesis he claimed that there are two elements of life: atoms and the void in which they exist and

move. He thought that atoms were indivisible, indestructible, and in motion. He also found

that atoms were infinite in number.

Dalton-1803

John Dalton was an English chemist, meteorologist, and physicist. He discovered the atomic theory in 1803. His theory insisted that matter is composed of atoms, all atoms of the same elements are identical. Atoms cannot be made or destroyed. Chemical reactions occur when atoms are rearranged. There are three types of atoms simple, compound and complex.

Dmitri Mendeleev- 1869

Dmitri Mendeleev, a Russian chemist and inventor who created the first version of the periodic table of elements. He laid out the element from lightest to heaviest and that’s when he realized their were gaps in the table. He predicted that some properties of elements were yet to be discovered but, already existed.

Dmitri Mendeleev’s Periodic Table

Eugene Goldstein-1885

Eugene Goldstein was a German physicist who, coined the term cathode rays for negatively charge electrons. He also discovered anode rays , the positively-charged particles formed when electrons are removed from the gas particles in a cathode-ray tube. He showed that cathode rays can cast shadows, then demonstrated how such rays are emitted, perpendicular to the cathode surface, and can be influenced with magnetic fields.

Henri Becquerel was a French physicist, who discovered radioactivity, by accident. He was unable to perform an experiment that he needed sunlight for because it was

raining. He wrapped his fluorescing crystals  in a black cloth, along with the photographic plate and a copper

Maltese cross, and waited for a sunnier day. A few days later, he unwrapped the crystals and found of that they were

emitting radiation because they were never exposed to sunlight.

Henri Becquerel- 1896

J.J. Thomson-1897

J.J. Thomson was a British physicist discovered the electron in 1897 through his experiments on the properties of cathode rays. His experiments suggested not only that cathode rays were over 1000 times lighter than the hydrogen atom, but also that their mass was the same whatever type of atom they came from. He also created the plum pudding model in which he said, “the electrons were embedded in the positive charge like plums in pudding.”

Ernest Rutherford-1907

Ernest Rutherford was a British chemist and physicist who later became known as the father of nuclear physics. He determined the structure of an atom and changed nitrogen to oxygen by splitting the atom’s nucleus. Also he discovered and named the nucleus and protons.

Millikan-1910

Robert Millikan was an American born experimental physicist. In 1910, he discovered the charge of the electron using his oil drop experiment. His experiment was based on Thomson’s but, he substituted oil instead of water. With this experiment, he was able to precisely measure the charge of an electron. When combined with the charge to mass ratio, he could then determine the mass of the electron. He was awarded the Nobel Prize in Physics for this experiment.

Niels Bohr was a Danish physicist. In 1913 he introduced his own model of a hydrogen atom called the Bohr model. This model showed that electrons orbit a positively-charged nucleus. He also said that the outer orbit could carry more

electrons than the inner orbits.

Niels Bohr -1913

Frederick Soddy-1913Frederick Soddy was an English radio chemist who proved the existence of isotopes of certain radioactive elements. He said that certain elements exist in two or more forms which have

different atomic weights but are still the same element. Isotopes occupy the same place in the Periodic table.

Heisenburg-1925

Heisenberg along with Max Born and Pascual Jordan created the matrix

formulation of quantum mechanics in 1925. This extended the bohr model by

describing how the quantum jumps occur. This result happened because the physical

properties of particles were interrupted and matrices were created.

The end!

Chadwick-1932James Chadwick was an English Nobel laureate in physics. In 1932 he discovered the existence of neutrons, the third piece of the atom to be found. Neutrons are particles with no charge. This discovery accelerated more findings in atomic physics.

CitationsSlide1Atomic model- http://www.glogster.com/media/1/6/41/7/6410729.gifSlide2Democritus- http://upload.wikimedia.org/wikipedia/commons/thumb/b/b9/Democritus2.jpg/200px-Democritus2.jpgSlide3Dalton’s atom model- http://www.kentchemistry.com/images/links/gases/1803_dalton2.jpgDalton- http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/Dalton_John_desk.jpg/240px-Dalton_John_desk.jpgSlide4Dmitri- http://upload.wikimedia.org/wikipedia/commons/thumb/c/c8/DIMendeleevCab.jpg/225px-DIMendeleevCab.jpgslide5Dmitri periodic table- http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Mendelejevs_periodiska_system_1871.png/550px-Mendelejevs_periodiska_system_1871.png

Citations(continued)Slide6Anode rays- http://cdn.dipity.com/uploads/events/408a819c9de9f4b075fe3376a5db007f_1M.pngSlide7Henri- http://www.daviddarling.info/images/Henri_Becquerel.jpgSlide8Plum pudding model- http://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Plum_pudding_atom.svg/220px-Plum_pudding_atom.svg.pngSlide9Ernest- http://extranet.kinnick.pac.dodea.edu/teachershtml/scott.andrews/physci/chem/cool_cats11/A1/e_ruther/images/ruther2.jpgSlide10Millikan- http://www.xtimeline.com/__UserPic_Large/6064/ELT200803021630362239380.JPGOil drop model- http://upload.wikimedia.org/wikipedia/commons/6/6f/Millikan%E2%80%99s_oil-drop_apparatus_1.jpg

Citations(continued)Slide11Bohr model- http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.pngSlide12Isotopes- http://1.bp.blogspot.com/-pN5hxFZswQ4/Thjy0KJdPQI/AAAAAAAAAHw/Lu4K8AX9-BQ/s1600/isotopes+of+hydrogen.jpgSlide 13Heisenberg- http://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Bundesarchiv_Bild183-R57262,_Werner_Heisenberg.jpg/225px-Bundesarchiv_Bild183-R57262,_Werner_Heisenberg.jpgSlide14Chadwick- http://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Chadwick.jpg/162px-Chadwick.jpg