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Chapter 4 Atomic Structure A Long, Long Time Ago… Greek Philosophers- 4 elements are Earth, Water, Fire, and Air Aristotle- first recorded atomic thoughts Matter is continuous (no atoms) Democritus (400 B.C.) - first recorded atomic theory Atoms are smallest part of matter, each type of matter has different atoms Aristotle and Democritus A Long Time Ago… Antoine Lavoisier (1782) – Used experiments in closed containers to develop the LCM Joseph Proust (1799) – Analyzed water to develop the Law of Definite Proportions John Dalton (1803) – Compiled past research to develop the first useful atomic theory Lavoisier and Proust John Dalton Dalton’s theory had 4 major tenets 1. 2. 3. 4. All matter is composed of atoms Atoms are indivisible Atoms of 1 element are alike, but different from those of other elements Atoms combine in small, whole number ratios to form compounds A Reminder Observation, Observation, Observation Research Hypothesis Experiment, Revise hypothesis lots of times Results match….may become a theory A Little While Ago… 1897- J.J. Thomson discovers the electron using a cathode ray tube Cathode Ray Tube Experiment http://www.aip.org/history/electron/jjappara. htm The Nucleus Exists! 1911- Ernest Rutherford uses the gold foil experiment to “discover” the nucleus The Gold Foil Experiment Results of Gold Foil Experiment… http://online.cctt.org/physicslab/content/Phy1/lesso nnotes/atomic/atomicmodelsandspectra.asp http://micro.magnet.fsu.edu/electromag/java/ruther ford/ Over 98% of the particles went straight through About 2% of the particles went through but were deflected by large angles About 0.01% of the particles bounced off the gold foil Rutherford’s Conclusion Rutherford's Nuclear Model 1. The atom contains a tiny dense center called the nucleus – the volume is about 1/10 trillionth the volume of the atom 2. The nucleus is essentially the entire mass of the atom 3. The nucleus is positively charged – the amount of positive charge of the nucleus balances the negative charge of the electrons 4. The electrons move around in the empty space of the atom surrounding the nucleus Understanding Periodic Blocks 19 K 39.0983 Atomic Number – # of protons Element Symbol Mass Number – Protons + Neutrons Can 20.0983 Neutrons Exist??? No, 39.0983 is an average mass of all natural K atoms – All K atoms MUST have 19 protons – Some have 20 neutrons, some 19, some 21… – Average is 20.0983 neutrons – Individual isotopes are identified by the number of neutrons Identifying Protons, Neutrons, and Electrons Chlorine-35 (element-mass number) # of protons = 17 # electrons = # protons # neutrons = mass number – protons – 35-17 = 18 Why no electrons in atomic mass? – Electron has mass 1/1837 of Proton and Neutron Nuclear Stability The Modern View of the Atom Neils Bohr (1913) develops the planetary model of the atom – Developed from “electrocution” of hydrogen gas – Only certain colors resulted – Why??? http://www.colorado.edu/physics/2000/qua ntumzone/index.html Bohr’s Hydrogen Atom http://www.visionlearning.com/library/m odule_viewer.php?mid=51 Schrodinger’s Revision… http://www.colorado.edu/physics/2000/quantumzone/schroedinger.html