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__**Henri Becquerel**__ Born in Paris, France on December 15, 1852. -Died in Le Croisic, France on August 25 1908.
 * __1875 - 1900__ **

Henri Becquerel was a French physicist born into a scientific family extending through several generations. The most famous of all is his grandfather Antoine-Cesar Becquerel. He received his formal scientific education at the École Polytechnique and training on engineering at the École des Ponts et Chaussées. Besides his teaching and research posts, Henri was appointed chief engineer in the Department of Bridges and Highways for many years. His research concerned electricity, energy, optical phenomena, and magnetism since these were major areas of study during the 19th century. Many years his main focus was the rotation of plane-polarized light by magnetic fields and then it was followed by infrared radiation. He examined the spectra of different phosphorescent crystals under infrared stimulation. Becquerel extended the research of his father by studying the similarity between absorption of light and emission of phosphorescence in some uranium compounds. Henri Becquerel was an accomplished and respected physicist by 1896.

Antoine Henri Becquerel made an accidental discovery. While he was studying the capability of uranium salts that had been exposed to sunbeams to fog photographic film plates. Since there were bad weather conditions, he could not expose the sample to sunlight. However, he accidentally left it on top of the photographic plate. When he developed the plate, he found out that the uranium salt still fogged the plate. Therefore, he proved his point that something that was very alike to X rays was released by luminescent substance at the same time it threw off visible radiation. His works awaken the world for the discovery of new radioactive materials. In addition, Henri made three other significant contributions. The first was to measure the deflection of beta particles. From the charge to mass value he got, he demonstrated that the beta particles were the same as Joseph Thomson’s newly identified electron. One more discovery was the condition that the supposedly active substance in uranium, uranium X, vanish its radiating capability.

 -Born in Cheetham Hill, a suburb of Manchester, England on December 18, 1856. -Died in Cambridge, UK on August 30, 1940. JJ Thomson’s father was a bookseller and therefore he did not have the fee for his apprenticeship. However, he wanted his son to be an engineer. Thomson entered Owens College. His professor of mathematics noticed his extraordinary intelligence and motivated him to apply for a scholarship at Trinity College in Cambridge. He was a student who finished the third year of math with first-class honors. JJ Thomson became Cavendish Professor of Physics in 1884. His discovery began one year later in the Cavendish laboratory where he conducted a series of experiments. The English physicist, JJ Thomson discovered the electron in 1897. “Electrons are negatively charged subatomic particles.” He performed many experiments that involved passing electric current at a low pressure through gases. In glass tubes, he sealed the gases and at both ends the tubes were fitted with metal disks called electrodes. These electrodes were attached to a source of electricity. There were two electrons. The anode became positively charged and the other one, the cathode, became negatively charged. The outcome was a glowing beam or cathode ray that traveled from the cathode to the anode. His investigations into the action of electrostatic and magnetic fields would later result in the invention of the mass spectrometer.
 * __JJ Thomson__**
 * Plum Pudding Model**

This model was proposed by JJ Thomson, the English physicist who discovered the electron. The plum pudding model is also known as the Chocolate Chip Cookie or the Blueberry Muffin Model. The “pudding” is positively charged and the plums dotting the dough are negatively charged electrons. This model has a dispersed positive charge in comparison to today’s atom which has a very small and dense positively charged nucleus. Therefore, this model of the atom was only successful to explain why most atoms were neutral. The Plum Pudding model was visualized as having a cloud of positive charge in contrast to the recent atomic model which illustrates a positive nucleus surrounded by an electron cloud.

**__1900 - 1915__** __** Marie Curie **__ -Born in Warsaw on November 7, 1867 -Died in Passy, France on July 4, 1934 Marie Curie was a Polish scientist. She was the youngest of four children. Her father was a physics teacher and her mother was also an educator. When she graduated with high honors in early schooling, she thought she had no option rather than having a higher education in Poland. In 1893, Marie Curie graduated in physics. Then, in 1894, she won a scholarship and returned to get a degree in mathematics. Through her work as a researcher, she met Pierre Curie and married to him in 1895. In 1897, Irene, her first child was born and then she continued to work on her research. She worked as a physics lecturer at a girls’ school. In 1903, her thesis resulted in the first advances scientific research to be awarded to a woman in France and the first doctorate in science awarded to a woman in all Europe. Marie Curie was a scientist whose research led to many discoveries about radiation and radioactive elements. Inspired by Henri Becquerel’s work on radioactivity she began to research on elements. First, she discovered radioactivity in thorium. Later, she demonstrated that the radioactivity is an atomic property, not a property of an interaction between elements as it was thought. In 1898, she worked with pitchblende and chalcolie, both uranium ores, to isolate this elements. She also published her hypothesis. In 1902, she was able to isolate pure radium. Her research was crucial for the understanding and for the use of newly discovered radioactive elements. In 1934, she died from leukemia caused by her long-term exposure to radiation.



__**Robert Millikan **__  -Born in Morrison, Illinois on March 22, 1868. -Died in San Marino, California on Dec 19, 1953. Robert Millikan is an American physicist. He grew up in various communities in the Mississippi River region. When he was fourteen, he took a job in a barrelhead factory for almost any pay. The earnings were about one dollar per day. Once he graduated from high school, he worked as a court reporter for a short period of time just before he entered Oberlin College in 1886. Millikan was requested to teach a physics course in his sophomore year. This request was odd since he had only one twelve week course in physics and did not have a big interest in the subject. Having necessity for money, he accepted the offer. Afterwards, he spent the summer teaching himself physics. In 1891 he received his bachelor’s degree and from then on continued to teach physics. In 1908, Millikan carried out several experiments to find the quantity of charge carried by an electron. He started by measuring the path of charged water droplets in an electrical field. The outcome suggested that the charge on the droplets is a multiple of the elementary electric charge. However, the results of the experiment were not precise. He obtained more accurate results with the oil-drop experiment conduced in 1910. In this experiment he replaced water with oil since water evaporated quickly. He sprayed a mist of droplets into a container. Next, he positioned an electrically charged plate above the chamber holding the droplets. Hence, two forces acted on the droplets, gravity and electrical field. The gravity was tending to pull them downward and the electrical field upward. By changing the electrical potential on the plate, he was able to keep the droplets suspended in space. The quantity by which the charge had to be adjusted was equal to the charge of the ion. The experiments yielded values for the charge of an electron, which are very close to those accepted today, 1.602177 x 10-19. An electron carries one unit of negative charge. Its mass is 1/1840 the mass of a hydrogen atom. 

__**Niels Bohr** __ <span style="color: #000000; display: block; font-family: 'Comic Sans MS',cursive; font-size: 99%; text-align: left;">- Date of Birth: Oct. 7 1885 - Date of Death: Nov. 18 1962 - Country of origin: Denmark Niels Bohr was the son of two physiology teachers, throughout his life, he grew up in an analytical environment and he was constantly exposed to new ideas. Since an earl age, Niels showed interest in Math and Physics; and he constantly used his dad's lab to make his experiments. It was in that lab that he made his work on surface tension for which he won a gold medal in 1906 by the Royal Danish Academy o Sciences. As he grew up, Rutherford became Borh's teacher. together they worked to improve Rutherford's atomis structure model. Bohr helped Rutherford by improving the structure model so that acording to quantum mechanics and physics, the model would fit more properly the traits found. Later, the Nazis entered Denmark and Bohr had to escape and he went to work in britain. There he started working on the atomic bomb. When Bohr saw how the atomic bomb was onl used for bad things, Bohr started a campaign with activities to show people how dangerous the bombs can be yet he wold also show positive and productive ways in which to use the atomic bomb. The discovery that Bohr made was about the atom structure. He modified Rutherford's model to fit the facts and properties about atoms that had been found. He made the electons be in levels around the nucleus instead of just floating around the nucleus. Bohr also found that the electrons were in specific levels that were ordered according to the amount of energy they had. The ones with the greatest amount of energy were in the outermost shell and the electrons with the least amount of energy were in the innermost shell around the nucleus. <span style="color: #0000ff; display: block; font-family: 'Comic Sans MS',cursive; font-size: 99%; text-align: left;">

__1915 - 1950__ **
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 * <span style="color: #0000ff; display: block; font-family: 'Comic Sans MS',cursive; font-size: 110%; text-align: left;">__Werner Heisenberg__ **

<span style="color: #000000; display: block; font-family: 'Comic Sans MS',cursive; font-size: 90%; text-align: left;"> -Born in Würzberg, Germany on December 5, 1901. -Died in Munich, W. Germany on February 1, 1976. Werner Heisenberg is a German physicist and philosopher. In 1920, he studied physics in the University of Munich. Under Neils Bohr, he was chosen Lecturer in Theorectical Physics at the University of Copenhagen in 1926. One year later, he was selected Professor of Theoretical Physics at the University of Leipzig. In 1929 he went abroad to Japan, United States and India to give lectures. He was appointed director of the Kaiser Wilhelm Institute for Physics as well as professor of physics at the University of Berlin in 1941. At the end of World War II, Heisenberg and other German physicists were taken to prison by the American troops. Then, they were sent to England. In 1946 he returned to Germany and with his colleagues, he reorganized the Institute for Physics at Gottingen, which was renamed the Max Planck Institute for Physics and Astrophysics. In 1925, Heisenberg discovered a way to formulate quantum mechanics in terms of matrices. He examined another feature of quantum mechanics that is missing in classical mechanics. He published his uncertainty principle which states that is not possible to know exactly at the same time, both the velocity and the position of a particle. This limitation applies for small particles such as electrons, but not for ordinary sized objects like cars. This discovery of matter paved the way for Erwin Schrödinger’s quantum mechanical description of electrons in atoms. Schrödinger’s theory includes the wavelike motion of matter as well as the uncertainty principle. On the other hand, Heisenberg made significant contributions to the theories of hydrodynamics of turbulent floes, ferromagnetism, the atomic nucleus, subatomic particles and cosmic rays. Heisenberg was involved in the preparation of the first West German nuclear reactor at Karlsruhe and a research reactor in Munich. Great argument surrounds his work on atomic research during WWII.

__<span style="color: #0000ff; display: block; font-family: 'Comic Sans MS',cursive; font-size: 110%; text-align: left;">**Erwin Schrödinger** __

<span style="display: block; font-family: 'Comic Sans MS',cursive; font-size: 90%; text-align: left;">-Born on August 12, 1887 in Vienna, Austria -Died in Alpbach, Austria on Jan. 4, 1961 Erwin Schrödinger was a bright, experimental and theoretical physicist. During the first half of the 20th century, he worked in Vienna and Berlin. Schrödinger was a major contributor to the wave theory of matter (a form of quantum physics). He developed a mathematical equation of wave mechanics that has his name. Erwin’s investigation was interrupted by two world wars. However, he still made advances in both quantum and color theory. In 1926, Erwin Schrödinger developed a mathematical equation to describe the movement of electrons in atoms or the behavior of the electron in a hydrogen atom. His work leads to the electron cloud model. The current explanation of electrons in atoms, the quantum mechanical model, comes from the mathematical solutions to his equation. This model determines the allowed energies an electron can have and how prone it is to find the electron in diverse locations around the nucleus.


 * Electron Cloud Model**

The electron cloud model is a visual model of the probable place of electrons in an atom. The probability of finding an electron is higher in the denser regions of the cloud. The nucleus contains protons and neutrons. Werner Heisenberg’s uncertainty principle contributed to the idea of the electron cloud model. His principle states that it is not possible to obtain precise values of both velocity and position of a particle at the same time. Heisenberg determined that the only way to describe the location of an electron in an atom is through probability distribution. This principle forms the basis of the electron cloud model. Erwin Schrödinger also contributed to the electron cloud model. He developed mathematical equations to describe the motion of electrons in atoms. Hence, his work also leads to the electron cloud model.