1900+-+1915

**__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__ ** **- 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. ** 


 * __The Planetary Model__ **




 * The Planetary model was made by Niels Bohr to explain his view of the atomic theory. The model includes a nucleus that is shown as the red and green spheres in the center of the atom and the electrons, the orange spheres, orbiting the nucleus in set levels. With his knowledge of physics and studing the research about atoms, Bohr created this model in which the electrons orbit the nucles like a moon orbits a planet; hence the name "planetary model". Like with the planets and the gravity, the electrons and proton's eletrical force are what keeps the electrons obriting the nucleus.

<span style="color: #36d1d3; display: block; font-family: 'Comic Sans MS',cursive; font-size: 130%; text-align: left;">__ Ernest Rutherford __ <span style="color: #a7e080; display: block; font-family: 'Comic Sans MS',cursive; font-size: 90%; text-align: left;">

- Date of Birth: August 30, 1871 - Date of Death: October, 19, 1937 - Country of Origin: New Zealand Rutherford went to Canterbury College in New Zealand University. There he graduated with a double first in math and physical science. Atfer graduating, he stayed in the college to do some research and with that he won a scholarship as a research student and he went to Cambridge to research with JJ Thompson. There he experimented a lot with rays and radioactivity.He then became the chair of physics in McGill University. There he worked on a project demonstrating that radioactivity came from atoms. This made him win the Nobel Prize in Chemistry in 1908. Then he became the chair of phisics in the University of Manchster where he discovered the nuclear nature of the atoms. By 1911, he studied the deflection of alpha particles shot through a gold foil where he established the nuclear theory of the atom. Rutherford did many discoveries regarding atoms. The first discovery that he did about atoms was that he found that radioactivity is the spontaneous disintegration of atoms. He found this by studying a sample of radioactive material and observing that it always took the same amount of time for half the sample to decay. With this he determined Earth's age. Thanks to finding out about the radioactive matter, he found "the nuclear nature of atoms, becoming the first successful 'alchemist': he converted nitrogen into oxygen." By the year 1911, he was studying about the deflection of ligt from alpha particles shot through gold foil, and with this he set the nuclear theory of the atom. By 1919 he had already disintegated nitrogen into hydrogen and water using a proton accelerator.

<span style="color: #36d1d3; display: block; font-family: 'Comic Sans MS',cursive; font-size: 130%; text-align: left;">__ Rutherford - Bohr Model __ <span style="color: #a7e080; display: block; font-family: 'Comic Sans MS',cursive; font-size: 90%; text-align: left;"> **

<span style="color: #a7e080; display: block; font-family: 'Comic Sans MS',cursive; font-size: 90%; text-align: left;">**In the Rutherford - Bohr model, The black dot in the center is the nucleus and the circles around it are the electron orbits. By this point, Rutherford and Bohr had found that the electrons orbited the nucleus in well defined orbits that were a specific distance from the nucleus. The electrons move from one orbit to the other by a change in energy. this change in energy is normally shown by an electromagnetic radiation.**