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Unit 3 Introduction • Complete Unit 3 PreTest on Edmodo • Go to class website for Unit 3 Resources (http://www.bcths.com/webpages/tprato/ne ws.cfm?subpage=465718 ) and open the “Atom Building Simulation Activity” • Complete the activity using the electronic directions and handout from teacher Key Terms from Simulation • Atomic Number – number of protons • Mass Number – sum of protons and neutrons • Neutral atom – number of protons and electrons is equal; net charge is zero • Ion – number of electrons is different than number of protons – Negative ion – more electrons than protons – Positive ion – less electrons than protons Key Terms/People to Identify • • • • • • • Isotope – Scientific Theory– Democritus– Dalton – Thompson – Rutherford – Bohr ‐ Symbol (inclusive of all key information) +1 net charge What are ISOTOPES? Atoms that have the same number of protons but different number of NEUTRONS 3 protons 3 neutrons 3 protons 4 neutrons 3 protons 5 neutrons Compare atomic numbers and mass numbers of these isotopes Isotopes have the same atomic number but different mass numbers! Mass # = 6, 7, 8 Atomic # = 3, 3, 3 3 protons 3 neutrons 3 protons 4 neutrons 3 protons 5 neutrons Isotopic Notation Nitrogen‐15 How is a Scientific Theory different from a non‐scientific theory? • As used in science, a theory is an explanation or model based on observation, experimentation, and reasoning, especially one that has been tested and confirmed as a general principle helping to explain and predict natural phenomena. – Any scientific theory must be based on a careful and rational examination of the facts. A clear distinction needs to be made between facts (things which can be observed and/or measured) and theories (explanations which correlate and interpret the facts). http://www.fsteiger.com/theory.html What gives a Scientific Theory validity? • Before a theory is given any credence in the scientific community, it must be subjected to "peer review." – This means that the proposed theory must be published in a legitimate scientific journal in order to provide the opportunity for other scientists to evaluate the relevant factual information and publish their conclusions. http://www.fsteiger.com/theory.html How does technology change what we know? • Can changes in technology change what we thought was once possible? • Can changes in technology change what we once thought to be an acceptable concept? • Can changes in technology change a scientific theory? Mobile Phone 1990 Cameras Printers Data Storage 1971 1976 1981 1.2 MB Up to 128 GB 1.4 MB Up to 4500 TB How do we define Scientific Theory? • A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. A theory is valid as long as there is no evidence to dispute it. When technology improves & new experiments are conducted, theories CAN CHANGE! http://www.livescience.com/21491‐what‐is‐a‐scientific‐theory‐definition‐of‐theory.html From Question to Theory Atomic Theory Learning Goals • To define and explain the model of atom • To identify by name the key scientists involved in evolution of atomic theory • To identify by sequence and scientist name, the process/test used and discovery made Democritus and his “atomos” • In Greek the term atomos means indivisible. • Democritus is credited for proposing the hypothesis that all matter is composed of atoms. 460‐370 B.C. John Dalton’s Atomic Theory (early 1800s – 5 hypotheses) 1. Atoms of any one element are identical to each other 2. Atoms of any two different elements are different 3. Atoms are indivisible 4. Compounds form as a result of atoms combining in whole # ratios during chemical reactions 5. When chemical reactions occur atoms rearrange to combine , but never form new atoms J.J. Thompson’s Cathode Tube Experiment (1897) Credited for discovery of the electron A ray of electrically charged particles could be produced by metal plates exposed to electrical current *The ray would interact with magnetic fields showing attraction or repulsion He shaped the view of the atom to begin to show a structure including loosely attached electrons which came to be known as the plum pudding model Cathode Ray Tube Demo #1 Cathode Ray Tube Demo #2 J.J. Thompson’s Cathode Tube Experiment (1897) Electrons (negative subatomic particles) were discovered J.J. Thompson’s Plum Pudding Model of Atom (1904) Rutherford’s Gold Foil Experiment • Credited for discovery of the nucleus of an atom • *He observed most alpha particles shot at gold foil passed straight through, a few are deflected off at angles, and some seem to bounce straight back toward source • He concluded that atom must be mostly empty space with a very tiny region of positive charge that is quite dense Gold Foil Demo #1 Rutherford Nuclear Model of Atom (1911) Dense Nucleus Empty Space Neils Bohr Planetary or Bohr Model of Atom (1913) With a positively charged nucleus, and negatively charged electrons, the electrons must have enough energy to keep them in constant motion around nucleus. What two hypotheses of Dalton’s Theory have been proven incorrect? Atoms of any one element are identical to each other –this is INCORRECT Atoms of the same element are nearly, but not exactly, the same (isotopes) Atoms are indivisible-this is INCORRECT Atoms are made up of smaller particles (protons, neutrons, electrons) Atomic Theory and Electron Configurations