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460
Democritus
460 BC
His theory was that all matter was made of smaller and smaller pieces of matter. He called the smallest piece of matter the atom which means 'not to be cut'. He believed that atoms were small hard particles that were made of the same material but were diffrent shapes and sizes. He also believed that atoms were infinite in number, and always moving. He believed that atoms had the capability of joining together. -
Dalton
Dalton's atomic theory was:
~all matter is made of atoms
~atoms are indivisible and indestrucable
~all atoms of a given element are identical in mass and properties
~compounds are formed by a combination of two or more diffrent types of atoms
~chemical reactions are a rearrangement of atoms
~atoms cannot be created or destroyed -
Goldstein
He discovered a positively charged particles by using a cathrode tube filled with helium gas. The positive charged particle had an equal and opposite charge to the electron. It had the mass of one atomic mass unit, or amu. This particle was named the proton. -
Thomson
Thomson first said that atoms were not hard solid spheres similiar to a billard ball. He said that atoms were a sphere of positive charge with negatively charged electons embedded in it, making it nuetrally charged. His atomic theory is also known as the plum pudding model. He is also first to suggest that atoms are not indivisible with his discovery of the electon. -
Rutherford
Rutherford proved that almost all of the mass of the atom is condensed in one area that is one billionth of the volume. He did this by shooting alpha particles at a gold sheet. Alpha particles are helium atoms without electrons, or with a positive charge. Because most of the alpha particles went straight through the gold sheet and only a few were deflected he was able to deduce that most of the atom is empty space. He also hypothesized that electrons orbit the nucleus. -
Millikan
He determined the charge of the electron. He did this with his oil drop expierement at the University of Chicago. This made it possible to calculate the mass of an electron. It also made it possible to calculate the mass of positively charged electrons. The formula he came up with was e=1.60x10^-19. -
Neils Bohr
Bohr discovered a lot of what we know about electrons. He proved that electrons orbit the nucleus without losing energy. Also, he proved they have fixed orbits of specific energy. He said that electrons wiht low energy orbit closer to the nucleus. While electrons with high energy orbit farther from the nucleus. -
Moseley
He was an English chemist. He discovered that x-rays emitted by the elements increased in a linear function. He proposed that this relationship was a function of the positive charge of the nucleus. With this new information he rearranged the periodic table. He ordered them according to thier atomic number instead of thier atomic mass. -
Erwin Schrodinger
He was an Austrian physicist. He created the electon cloud model. He developed a probability function for hydrogen and a few other atoms about where the electrons should be. This is called the quantum mechanical model. It is the modern description of electrons in atoms. -
Chadwick
He was an Engllish physicist. He is famous for the discovery of the nuetron. This was previously unknown mainly becuase it does not have an electrical charge. This discovery also explained the existence of isotopes. He was awarded the Nobel Prize for Physics in 1935 for his discovery of the nuetron.
