Fall.2010.MMA.Lester.atomictimeline

= Atomic Timeline =

= Ancient Times (450 AD and years prior) =

**__Leucippus__ (5th Century BC)**
Leucippus is accredited with the original idea of the two substances that make up the universe: the full and the void. He also stated that atoms are always in motion. Not much else if known in regard to his work because it is mostly overshadowed by Democritus’ work.

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**__ Democritus __**** (460-370 B.C.) **
Democritus was born in Thrace, Greece around 460 BC. He expanded on Leucippus’s ideas of matter: all matter was made up of what he called atoms, tiny indestructible units. Atoms were always in motion, and anything in between atoms was empty space. They were also indestructible. He had barely any evidence and used no experiments. The theory was later expanded to show that the property of a substance depended on the shape and size of the atoms.

[|http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec05.html]



**__ Aristotle __**** (384-322 B.C.) **
Aristotle was born in Stageria, Greece in 384 BC. He studied at the Platonic Academy in Athens for 20 years. In 343 BC, he went to tutor Alexander the Great under the invitation from the latter’s father, Philip II of Macedon. There he eventually became the head of the royal academy in Macedon. In 335 BC he returned to Athens and established his own school, the Lyceum. Between 335-323, Aristotle worked in the following subjects: physics, biology, medicine, metaphysics, and philosophy. His contribution to atomic theory was this: matter makes up five elements: fire, earth, air, water, and aether. However, he did not believe in the atom.

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= = = 1700-1800 =

**__ Antoine Lavoisier __**** (1743-1794) **
Antoine-Laurent Lavoisier was born in Paris, France in August 1743. After studying math, chemistry, astronomy, and botany at the College Mazarin from 1754-1761, he became a member of the French Academy of Sciences in 1768. In 1775 he was appointed to the position of commissioner for the Royal Gunpowder and Saltpeter administration. Lavoisier experimented with combustion and oxygen, although not called oxygen until he named it so. He did studies about the role of oxygen in animal and plant respiration, its effect of metals, and it being one of two materials needed for a combustion reaction. His results supported the law of conservation of mass, although this law was not yet formulated. In 1789 he published Traité Élémentaire de Chimie (Elementary Treatise of Chemistry), which for all purposes was the first chemistry textbook. He was beheaded in 1794 during the Reign of Terror of the French Revolution for being a former tax collector.

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**__ Joseph Proust __**** (1754-1826) **
Joseph Proust was born in Angers, France in September 1754. He learned chemistry and was trained as an apothecary by his father. He taught at the Chemistry School in Segovia and the University of Salamanca; both were located in Spain, and he returned to France after his laboratory located at the latter was burned by Napoleon’s armies. His most important contribution was the Law of Definite Proportions. Using copper carbonate in his experiments, he determined that the ratio of the elements in a given compound would always remain constant, regardless of the amount of compounds. These findings were published in 1799. He died in July 1826.

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= 1800-1875 =



**__John Dalton__** **(1766-1844)**
John Dalton was born in Cumberland, England in 1766. He received a grammar school education, was taught math by a relative, and gained much of his scientific knowledge from the instruction of a blind philosopher named John Gough. In 1787 he started recording daily weather readings, compiling much data. In 1793, he moved to Manchester and started teaching at the New College in Moseley Street. There, Dalton joined the Manchester Literary and Philosophical Society. He shared papers and essays with the society and also wrote a book, //Meteorological Observations, in 1793. His most important contribution to the world of Chemistry is the Atomic Theory, developed between 1802-1804. He determined four principles of atoms:// 1. Elements consist of tiny particles called atoms. 2. All atoms of the same element are identical and have the same mass. 3. Compounds consist of different elements combined together. 4. The combination of those atoms can be rearranged by a chemical reaction. In 1817, until his death in 1844, he became president of the society.

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**__ Amedeo Avogadro __ (1776-1856)**
Lorenzo Romano Amedeo Carlo Avogadro, conte di Quaregna e di Cerreto was born in Turin, Italy in August 1776. In 1796 at the age of 20, he obtained a degree in ecclesiastical law, following in his father’s footsteps. After practicing as a lawyer for several years, he was given a private education for math and science. In 1811 he hypothesized that equal volumes of gases, at the same temperature and pressure, contain the same number of molecules. He also thought that molecules could be further broken down into smaller units. His ideas were not fully taken into consideration until after his death, around 1858; Avogadro’s Number, named in honor of him, was discovered as the number of molecules in one mole of an element. A reason for this posthumous discovery was because being Italy, he was far away from the main science centers of Europe. He died in July 1856.

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__ Dmitri Mendeleev __ (1834-1907)
Dmitri Mendeleev was born in Tobolsk, Siberia in 1834. He graduated from the University of St. Petersburg in 1856 with a science degree. He became a professor in 1863 and Chair of the University in 1866. In 1869, Mendeleev’s most important work was published in his book //Principles of Chemistry//. He had taken the 63 known elements and arranged them in order of atomic masses. By doing this, he was able to group the elements by similarities in properties and leaving spaces for elements yet to be discovered. His new table also showed which accepted atomic masses were wrong. Later he did some work regarding the temperature of gases and thermal expansion of liquids. He died in 1907.

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= 1875-1900 =



**__Wilhelm C. Röntgen__** **(1845-1923)**
Wilhelm Conrad Rontgen was born in Lennep, Germany in 1845. He attending the Polytechnic at Zurich and attained his Ph.D. from the University of Zurich in 1869. In 1875 he was selected as the Professor in the Academy of Agriculture at Hohenheim in Württemberg. He became the Chair of Physics in the University of Giessen in 1879. In November 1895, while experimenting with the Crookes tube in a dark room, he discovered the usefulness of the radiation it emitted. He found that different objects inhibited the rays in varying degrees of transparency. He put his wife’s hand in front of the rays, and it cast an image of her bones, with a ring on her finger. It did not show her skin because of the difference of permeability by the rays. He named them “X-Rays” because he did not fully understand what they were or how they worked. As a result of his findings, streets were named after him, and he was given all sorts of honorary degrees, prizes, awards, and medals. He died in February 1923.

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**__Henri Becquerel__ (1852-1908)**
Antoine Henri Becquerel was born in Paris, France in December 1852. He had inherited a tradition of academic excellence: his father was a Professor of Applied Physics and his grandfather was a Fellow of the Royal Society. Becquerel began his advanced education at the Polytechnic in 1872. He was given the position of Chair of Applied Physics at the Conservatoire des Arts et Metiers at the Museum of Natural History in 1878. He began work on X-Rays, previously discovered by Rontgen, and radiation. He was able to deflect the radiation rays of naturally phosphorescent uranium salts by electric or magnetic fields. Thus, he discovered spontaneous radioactivity, and was given half of the Nobel Prize for Physics in 1903. The other half was given to the Curies for their study of his discovery. He died in August 1908.

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**__J.J. Thomson__ (1856-1940)**
Joseph John Thomson was born in Manchester, England in December 1856. He attended Owens College in 1870, Trinity College in 1876, and then went on to become Cavendish Professor of Experimental Physics at Cambridge in 1884. In 1895 while working in the Cavendish Laboratory, Thomson began his pursuit of the electron. Using the Crooke’s tube which emitted cathode rays, he found the electrically charged particle. This was the first subatomic particle to be discovered. Thomson received the Nobel Prize for Physics in 1906, and he was knighted in 1908. Before World War I, he discovered the isotope. Thomson died in August 1940.

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= 1900-1915 =



**__ Marie Curie __**** (1867-1934) **
Marie Curie was born Marie Sklodowska in Warsaw, Poland in 1867. Her father gave her some scientific training, but the rest of her education came from general education. After some hard times and monetary deficiency, she finally moved to Paris to attend the Sorbonne and study chemistry and physics. Here she met Pierre Curie, a professor at the university, in 1894 and married him the following year. Together with her husband they studied radioactivity, previously discovered by Henri Becquerel in 1896. In 1902 they announced the discovery of two new elements, Polonium, named after Marie’s home country, and Radium. Along with Becquerel, they were awarded the Nobel Prize for Physics in 1903. After Pierre was killed in 1906 in a traffic accident, Marie assumed his position as Professor of General Physics at the Sorbonne. In 1911 she was awarded the Nobel Prize for Chemistry for isolating pure radium. Because of her hard work, she became the first woman to receive a Nobel Prize and the first woman professor at the Sorbonne. Marie died of leukemia in 1934.

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**__Robert Millikan__ (1868-1953)**
Robert Andrews Millikan was born in Morrison, Illinois in 1868. He received an elementary education and went on to Oberlin College in 1886. From 1891-1893 he worked as a physics teacher; it was then that he realized his love of physics. By 1895 he had attained hi Ph.D. and was named Fellow in Physics at Columbia University. The following year he spent time at the Universities of Berlin and Göttingen. When he returned he was invited to become the assistant of the Ryerson Laboratory at the University of Chicago. Between 1909-1910 he developed and perfected a method to determine the charge of the electron, what became known as the “oil-drop experiment” or the “falling-drop experiment.” He continued working in the field of physics: he verified the photoelectric equation proposed by Einstein and applied this to Planck’s constant //h//. He died in December 1953.

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**__Ernest Rutherford__ (1871-1937)**
Ernest Rutherford was born in Nelson, New Zealand in August 1871. After getting an elementary education, he received several scholarships, allowing him to attend first Canterbury College, then Trinity College. He began work in the Cavendish Laboratory under J.J. Thomson in 1894. He moved to other laboratories and collaborated with many other scientists. In his work over the years, he discovered a new noble gas, thoron, and developed the “disintegration theory” attributing radioactive phenomena to atoms, not molecules. Rutherford’s most famous experiment was the “gold foil experiment.” This included shooting alpha particles at an extremely thin piece of gold. He expected the alpha particles to go directly through it; however he found an extremely important discovery. Some of the particles bounced off in different directions, including back towards him. This disproved J.J. Thomson’s “plum pudding” model of the atom, because Rutherford concluded that there must be some spot with a mass in the center of the atom. According to him, his “nucleus” contained the entire mass of the atom as well as the positive charge. He performed many other experiments pertaining to the atom, but his greatest contribution was the discovery of the nucleus. He received the Nobel Prize for Chemistry in 1908. Rutherford died in October 1937.

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= 1915-1950 =



**__ Niels Bohr __**** (1885-1962) **
Niels Henrik David Bohr was born in Copenhagen, Denmark in October 1885. His father, Christian, was Professor of Physiology at the University of Copenhagen. After Bohr received his Master's Degree in Physics in 1909 and his Doctorate in 1911, he worked in the laboratories of both Rutherford and Thomson. During this time he developed a model of the atom based on the idea that electrons travel in orbits around the nucleus. He also concluded in his work that an element's characteristics were based on //how many// electrons were in orbit and that electrons could jump from a higher orbit to a lower orbit, giving off a photon of light. His model of the atom only gave off radiation when electrons made that jump. He attained the position of Professor of theoretical physics at the University of Copenhagen in 1916. Six years later he was given the Nobel Prize for Physics. Threatened by arrest from the Germans in 1943 Bohr fled Denmark and brought his family to the United States. He was put to work on the Manhattan Project as a "knowledgeable consultant" under the name of Nicholas Baker. Following the war, he went back to Denmark and preached the responsible nuclear usage by human beings. He died in November 1962.

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**__Erwin Schrodinger__ (1887-1961)**
Erwin Schrodinger was born in Vienna, Austria in August 1887. As a child he loved math and science. In 1906 he attended the University of Vienna, and starting in 1920, he took up several academic posts throughout Germany and Poland. Around 1925 he became obsessed with Louis de Broglie’s theory about electron movement. Schrodinger expanded upon de Broglie’s work, but instead of using particles of the quantum theory, he used waves. In short, he discovered the wave/particle duality of quantum mechanics and also created an equation to accompany it. He received half of the Nobel Prize in Physics in1933, the other half being given to Paul Dirac. In 1927 he moved the University of Berlin to teach, where he met Albert Einstein. In 1933 he fled Nazi Germany and went to England; he did not like the policies of the Nazi regime. He continued to publish papers and took up many esteemed positions until his death in January 1961.

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**__ James Chadwick __**** (1891-1974) **
James Chadwick was born in Cheshire, England in October 1891. He worked in the Manchester laboratory under Rutherford and received a Master's Degree in Physics in 1913. During World War I he interned in Berlin, Germany. Following the end of the war, he returned to England where he again worked with Rutherford who had moved to the Cavendish Laboratory in Cambridge. He was elected Fellow of Gonville and Caius College in 1921 and Fellow of the Royal Society in 1927. In 1932 after many years of hard work and dedication, Chadwick proved the existence of neutrons and their neutral charge. Unwittingly, Chadwick paved the way for nuclear fission and the development of the atomic bomb. Subsequently he was awarded the Nobel Prize for Physics in 1935. Between 1943-1946, he worked on the Manhattan Project in the United States. Aside from many awards and titles he gained throughout his many successful years as a scientist, he was knighted by King George IV in 1945. He died in July 1974.

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**__Werner Heisenberg__ (1901-1976)**
Werner Heisenberg was born in Würzburg, Germany in 1901. After attending the Maximilian school at Munich until 1920, he went on to the University of Munich to study physics. Gaining his Ph.D. in 1923, he was made Assistant to Max Born at the University of Göttingen. The following two years he worked with Niels Bohr at the University of Copenhagen. His most important contribution to the world of chemistry was the theory of quantum mechanics, more specifically the //principle of uncertainty.// He stated that one cannot know the specific location of an electron in motion, so one cannot know that Bohr’s electron orbital models even exist. He also said that the mechanical quantities should be measured in abstract structures, matrices, which he later created. His findings paved the way for the discovery of allotropic forms of hydrogen, and he won the Nobel Prize for Physics in 1932. He died in February 1976.

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= Models =



**__Small, spherical, solid, invisible model__**
This model was first described by Democritus. He held the belief that the atom was the smallest piece of matter that could not be divided any further. He thought that when the small spheres connected with others, they created properties of certain substances. He also thought that individual atoms were invisible, but when massed together, they created something visible.



__ Electron Cloud Model __
A product of Schrodinger's experiments and research, the electron cloud model shows the probability of position of electrons in an atom. The many blue specs around the nucleus exhibit where an electron could be. Since the exact position and velocity of an electron can never be calculated, this model provides an estimation.



__**Plum Pudding Model**__
Developed by Thomson, this model placed the electrons throughout the atom like the plums in plum pudding. Everything else in the atom was positive space like the pudding.



__Rutherford-Bohr Model__
After completing the gold-foil experiment, Rutherford proves Thomson's model wrong. He discovered a positively charged mass in the center of an atom, although extremely small relative to the size of the entire atom.



__Planetary Model__
This model was developed by Bohr. It shows that electrons can be on different shaped orbits, not just spherical ones. It also allows the electrons to have different spins.