History+of+the+Atomic+Model--Unit+2

(1) Who first thought of the idea of the atom? How was his idea accepted? Democritus first thought of the atom. No one really accepted his ideas because Aristotle disagreed with him, and everyone went with what Aristotle said. Korey Burton (That's right! Mrs. K) (2) Describe the postulates of Dalton’s understanding of the atom. Daltons postulates were that all matter is composed of small, indivisible particles called atoms. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more atoms in definite arrangements in the ratio of small whole numbers. atoms are not created, destroyed, or converted into other kinds of atoms during chemical reactions.-David Smith (Good job David--Mrs. K.) (3) What did Henri Becquerel discover? How did it happen? Henri Becquerel discovered x-rays. This happened when he was conducting an experiment which started with the exposure of a uranium-bearing crystal to sunlight. -Heather Roane (The uranium exposed photographic film like light does--Mrs. K.) (4) What did J.J. Thomson discover? Briefly describe how he did this. In 1897, J.J. Thomson discovered the electron in a series of experiements designed to study the electric charge in a high-vacuum cathode-ray tube. In 1904, he suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. -- Lauren Rich (Good job, Lauren--Mrs. K) (5) What was J.J. Thomson’s model of the atom called? Describe it. J.J. Thomson's model was called the Plum Pudding Model or simply the Thomson Model. The Model looked like a ball of bread with raisins, nuts, and some other stuff all in it. The bread symbolizes the charges material inside the atom and the nuts and raisins symoblize the electrons. (Who are you? Thomson said that the atom was a ball of positive charge with negative charges scattered throughout--kind of like a blueberry muffin. The muffin is positive charge and the blueberries are negative charges. Mrs. K.) (6) What did Millikan find out about the electron? Briefly describe his experiment. Millikan found the charge of an electron to be 1.602 x 10^-19. The oil-drop experiment: Millikan let oil drip through a hole between two charged plates into a bottom chamber. He then filled the chamber with x-rays, making the air particles lose electrons. The oil drops captured some of the extra electrons which gave them an electric charge. Then Millikan created an electrical field between the two plates that made the drops hang suspended in midair. Finally, he used the formula: m x g = q x E. -Kelli Johnson (Great answer Kelli! Of course, you do not have to worry about remembering the formula, I just want you to be familiar with his experiment. Mrs. K.) (7) Describe Rutherford’s gold foil experiment. Rutherford's experiment showed us that electrons move around the nucleus; they do not remain in a fixed, constant location. He also concluded that an atom was made of a positively charged nucleus encircled by empty space where the electrons orbited. He came to this conclusion through his gold foil experiment. In the experiment he used a thin gold foil which he struck with a steady stream of alpha particles with a 2 + charge. Most of the particles in his experiment passed through the foil, but others were deflected. The deflection proved that the nucleus is, in fact,positively charged because the Alpha particles were repelled. He also found that, due to the fact that most of the particles passed through, most of the atom is composed of empty space. --Logan Griffis (Good description Logan--Mrs. K.) (8) What significant information was learned from Rutherford’s gold foil experiment? The results of the Rutherford experiment lead to the proof of an atomic nucleus, disproving the plum pudding model.--Brian West (He learned that the atoms was mostly empty space, but it had a small dense, positivly charged center--Mrs. K.)

The most significant information learned, was that J. J. Thomson’s Plum Pudding Model of the atom was incorrect. The way that the positive particles bounced off the thin foil showed that the majority of the mass of an atom was concentrated in one area. Because the majority of the positive particles continued on their original path, Rutherford concluded that the other portion of the atom was a region of low density. -Taylor Johnson (Good explanation Taylor! Mrs. K.)

(9) Describe Bohr’s model of the atom.

(10) What particle did Chadwick discover? Why was this particle more difficult to identify?

(11) What is our current understanding of the structure of the atom?