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WHAT IS MATTER MADE OF? 5 THEORIES OF MATTER 1. Fire, air, water and earth 2. Tiny, solid particles called atoms 3. Lumps of positively charged material with negative electrons all through it 3. A positive nucleus with negative electrons moving around it 5. A positive nucleus with electrons orbiting around it WHAT IS MATTER MADE OF? • Empedocles was a Greek philosopher and scientist • He said that matter is made of: Why might that make sense to people who knew nothing about atoms? SO WHAT IS MATTER MADE OF? John Dalton, who lived in the early 1800s, said: 1. Matter is made up of tiny particles called atoms 2. Atoms can’t be created, or destroyed 3. All atoms of the same element are identical and are different from atoms of all other elements 4. Different elements link together, in defined whole number ratios, to make compounds Atoms are the smallest particles and don’t have distinct parts Dalton’s atom John Dalton, who lived in the early 1800s, said: 1. Matter is made up of tiny particles called atoms Introduction to the Atom @ http://www.khanacademy.org/ http://www.youtube.com/watch?v=1xSQlwWGT8M&feature=fvwrel Dalton also said: 2. Atoms cannot be created or destroyed Dalton also said: 3. All Elements have Unique Atoms Lithium Gold Sodium Hydrogen Uranium Dalton also said: 2. Dalton also said: 4. Elements combine in defined, whole number ratios H2O – water not H2O – water vs. oxygen ¾ oxygen oxygen hydrogen hydrogen ½ hydrogen hydrogen oxygen oxygen oxygen ½ hydrogen hydrogen hydrogen hydrogen Dalton also said: 3. Joseph John Thomson in 1897: 1. Discovered that atoms have negatively charged particles in them 2. Concluded that since atoms are neutral they must also contain positive particles to balance the negatively charged particles 3. Proposed that the atom is a lump of positively charged material with negative electrons all through it Atoms aren’t the smallest particles and do have distinct parts; a positive body and electrons your textbook’s version Thomson’s atom positive material negative electrons How Thomson Found Negative Particles Discharge Tube Air at Very Low Pressure 1. He used a cathode ray tube like these ones 2. The tubes contain small amounts of gas 3. He used electricity to run a current through the gas in the tube 4. The gas glowed 5. The glow started from the negative end and went to the positive end 6. Opposites attract so if the glow moved towards the positive end that meant it must have been negative 7. That meant some kind of negative things from the atoms were moving 8. We now call these particles electrons Cathode Green Glow Anode To Vacuum Pump High voltage Production of Cathode Rays Generator Production of Cathode Rays Green Glow Direction Green Glow Starts Here Discharge Tube Air at Very Low Pressure Cathode Green Glow Anode Green Glow Moves to Here To Vacuum Pump High voltage Production of Cathode Rays Generator Green Glow Direction Thomson’s Cathode Ray Experiment Evidence of Electrons Ernest Rutherford’s 1907 study of atomic structure: 1. He fired very tiny, fast, positive alpha particles at a very thin sheet of gold foil 2. He expected the alpha particles to just pass straight through the spaces between the particles in the foil 3. Some passed straight through, some veered off on angles, and some bounced back 4. He concluded that atoms must have a positive core that the alpha particles were hitting 5. He named this core the nucleus and proposed that the electrons revolved around the nucleus Atoms aren’t the smallest particles and do have distinct parts; a positive nucleus and electrons Rutherford’s atom positive nucleus revolving electrons Rutherford’s Gold Foil Experiment Apparatus for experiment Path of alpha (α) particles Neils Bohr in 1912: why don’t negative electrons collapse into the positive nucleus? 1. He thought Rutherford’s model was fundamentally correct just not complete 2. Something must be keeping the electrons from collapsing into the nucleus 3. He determined that electrons only move in defined orbitals around the nucleus 4. For electrons to move between orbitals they need specific amounts of energy 5. He called these bundles of energy quanta Atoms have distinct parts; a positive nucleus and electrons that revolve around it in orbitals Bohr-Rutherford atom Evolution of the Atomic Model to be continued … 1. Dalton’s atom 2. Thomson’s atom 3. Rutherford’s atom Atomic Theorists on Teacher Tube videos http://streaming.teachertube.com/viewVideo.php?title=Atomic_Theorists&video_id=86254 4. Bohr-Rutherford atom