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Warm-up On your group white board describe an atom: structure, components etc You can use drawings (labels!) or words Atomic Model Theory and how it evolved Video timeline of discoveries How scientific theories and models evolve…. science is a process many scientists contribute to it the model changes over time the model will change in the future as more research leads to new discoveries 400 BC Democritus Invented the word! Atom “The smallest particle of matter is indivisible and indestructible and I will call it “atomos” (atom) John Dalton 1802 isolated 20 pure substances he called them “elements” and gave them name, symbols and weights Made the first periodic table The first atomic theory 1st atomic Theory: 1. Matter is made up of atoms: tiny, indivisible 2. Atoms of the same element are identical and different from other elements. 3. Chemical Rx: atoms can be joined into compounds, separated or rearranged Subatomic Particle Discovery JJ. Thompson’s 1897 - Cathode Ray experiment Key Experiments: Cathode Ray Machine Cathode: negative electrode Anode: positive electrode Observation: cathode ray beam is attracted to a positive pole and rejected by a negative pole Conclusion: The beam is composed of ____________ charged particles Thompson called them Electrons New Atomic Model Plum Pudding Model Electrons are embedded in a positively charged matrix and they are overall neutral Goldfoil Experiment 1917 Rutherford: “Blasted” ultra thin gold foil with Alpha particles (nuclei) Theory: alpha particles should go straight through the plum pudding. Goldfoil/Alpha particle Machine Observation: most go through but a few get deflected at odd angles??? What’s in the center of an atom? There is something hard, impenetrable in an atom that deflects alpha particles Solar System Model Solar System Model – nucleus in the center, electrons orbiting like “planets” Atoms are mostly empty space containing negative electrons there is a small, dense positively charged nucleus in the center Quantum Mechanical/Bohr’s Model Niels Bohr and Max Planck 1920’s What’s a quantum? Theory: Electrons occupy distinct energy levels. They can move up or down levels by releasing or absorbing energy units called quantums Warm-up Sketch Thompson’s experimental set up and explain how he concluded that the Cathode Ray was negatively charged Sketch Rutherford’s experimental set up and explain how he determined that an atom is mostly empty space but has a small hard nucleus Current Atomic Model Nucleus Electron Orbital Clouds Current Atomic Model Summary Nucleus: small, dense, contains defined numbers of protons: p+ ,positive charge, mass: 1 amu neutrons: no , neutral charge, mass: 1 amu Number of p+ and no in the nucleus can only be changed in a nuclear reaction Space surrounding nucleus: contains Electrons: e-, negative charge, “no mass” are in constant, extremely fast motion Occupy special shaped orbital clouds Can be easily removed (electricity), added (ions) or rearranged (chemical Rx) Size and Mass of Atoms Size : measured in Ångstrǿm: 1Å=1.0 x10-11m Mass: measured in atomic mass units: 1 amu = 1/12th of the mass of a Carbon-12 atom = 1.64 x 10-24 grams Some electrons do orbit in spherical motion, others in dumbbell shaped clouds Practice What is the mass in amu of 45 Protons? 45 amu 2. What is the mass in gram of 45 Protons? 45 x 1.64 x 10-24 g = 73.8 x 10-24 g 7.38 x 10-23 g 1. Practice 3. What is the mass of an element with 5 protons and 7 neutrons? 12 amu 4. What is the size of an element with a width of 45 Ångstrøm in meters? 45 x 1.0 x 10-11 m= 45 x 10-11m = 4.5 x 10 -10 m 5. Calculate mass and charge of an element with A. 8 protons, 8 neutrons and 10 electrons? 16 amu, 2B. 15 protons, 17 neutrons, 18 electrons 32 amu, 3C. 12 protons, 13 neutrons, 10 electrons 25 amu, 2+ D. 6 protons, 8 neutrons, 6 electrons 14 amu, 0 Warmup 1. What is the mass in amu’s of an element with 33 protons and 37 neutrons? 2. Name the element. 3. What is the mass in grams of an element weighing 23.5 amu’s? 4. What size in meters does an element with 1078 Angstrom have? Journal 1. Name the element of the three isotopes shown below 2. Write the two short hands 3. Indicate the # p+, no, e- for each A B C Isotope Videos Carbon Isotopes Name the following mean elements 1. 2. 3. 4. 5. 6. 7. 8. 9. Hg Sn Mn Zn As Au Pb At Sb Find the symbol of the following 1. 2. 3. 4. 5. 6. 7. 8. 9. Manganese Zinc Antimony Mercury Lead Arsenic Tin Gold Astatine Find the AAM of Element Terminium 83.25% 23.015 amu 6.78% 24.111 amu 9.97% 25.000 amu