1900AD-1915AD

=Robert Millikan 1909= Robert Millikan was born in 1868 in America. He was an experimental physicist. He is know for his discovery of the charge of the electron and the photoelectric effect. Millikan worked on an experiment involving oil droplets. He measured the charge of the oil droplet when it was suspended between a positive and negative metal plate. This showed that electrons have charges. The charge of an atom is one of the most important things to know about in an atom. He found the charge on as to be 1.592 X 10-19. He was slightly off since the actual charge is 1.602 176 53(14) x 10 -19. =Ernest Rutheford 1911= Ernest Rutheford was Born in Brightwater, New Zealand in 1871. He is best know for his atomic model. He discovered that the atom has a posatively charged nucleus surrounded by negatively charged electrons. He shot radioactive particles through a very thin piece of gold foil. He picked them up on the other side of the gold foil with a screen. Most of the particles went through like he expected, but some of the particles bounced off. This meant that there was a centralized mass. This mass was the nucleus. This is a picture of his experiment =Rutheford's Model= == Rutheford's model was the first atomic model to have a centralized mass called a nucleus and electrons orbiting around it. SInce only 1 in about 8000 particles bounced back off the foil, this led him to believe that most of the atom was empty space. This was a major step foreword compared to the Plum Pudding model. The atomic structure was now known. ** Niels Bohr 1913**  Neils Bohr was born on October 7, 1885 in Copenhagen, Denmark. In 1922 he won the nobel peace prize for physics. Bohr was a professor at the unoversity of Copenhagen. Neils Bohr produced a theory about the structure of an atom based on Rutheford's Plum Pudding model. Bohr discovered that the electrons travel in orbits. Outer obrits could hold more electrons than the inner orbits. He suggested that when an electron jumps from an outer orbit to an inner orbit it emits light. Video Explaining Bohr's model [|http://www.youtube.com/watch?v=wCCz20JOXXk] =The Planetary Model 1915= ==

This model was created by Neils Bohr in 1915. In the center is the nucleus which is composed of protons and neutrons. It is orbited by electrons. The nucleus is about 100,000 times smaller than the radius of the atom.