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Atoms

Atoms. The History of the Discovery. Atoms. John Dalton’s Atomic Theory All matter is made up of atoms. They are indivisible objects. Atoms of the same element are identical Atoms can physically or chemically mix in whole number ratios to produce compounds

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Atoms

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  1. Atoms The History of the Discovery

  2. Atoms • John Dalton’s Atomic Theory • All matter is made up of atoms. They are indivisible objects. • Atoms of the same element are identical • Atoms can physically or chemically mix in whole number ratios to produce compounds • Chemical reactions occur when combining, separating, or rearranging atoms. Atoms are never created nor destroyed.

  3. Atoms • Some interesting facts about atoms • Atoms consist of protons, neutron and electrons • The atom is the smallest unit that has the properties of an element. • The size of an atom is about 50-150 pm about 3.0 x 10-11 meters • One teaspoon of water contains about 3x as many atoms as the Atlantic Ocean contains teaspoons of water.

  4. Electron • Discovered by J.J. Thomson (1856-1909) in 1897. • Used a cathode ray tube to determine the existence of the electron. • A tube filled with a gas at low pressure with two electrodes (one at either end).

  5. Electrons • He then passed a charge through the electrodes and one became positive (anode) and the other was negative (cathode). • He discovered a beam that traveled from the cathode to the anode (- to +). • Thomson then brought plates with positive and negative charge and discovered the beam was attracted to the + plate.

  6. Protons • Atoms have no net charge • Electric charges are carried by particles of matter • Electric charges exist as whole numbers (you can not have half of a – charge) • The number of positive particles must equal the number of negative charges.

  7. Protons • E. Goldstein discovered rays going in the opposite direction of the cathode rays and called these canal rays. They moved from positive to negative (anode to cathode, or + to -).

  8. Neutron • Discovered by James Chadwick – No net charge, just mass.

  9. Nucleus • Discovered by Ernest Rutherford – a student of J.J. Thomson. • Used gold foil, fluorescent screen, and alpha beam. • He took a thin sheet of gold foil and placed it in the center of a fluorescent screen. Then he directed alpha particles toward the gold foil. He predicted that a majority of the alpha particles would pass through the gold foil and some would be deflected at small angles.

  10. Nucleus • He discovered most of the particles passed directly through but the angles of reflection were great. Some of the alpha particles even bounced directly back. • This suggested there was a large mass in the center of the atom.

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