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Dr. Williamson’s Atoms ppt © vm williamson Atoms Dr. V.M. Williamson Democritus ! Greek philosopher Democritus began the search for a description of matter more than ______ years ago. " He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided? Atomos 400 BC ! His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained. ! This piece would be _________________. ! He named the smallest piece of matter “atomos,” meaning “not to be cut.” 1 Dr. Williamson’s Atoms ppt Atomos # To Democritus, atoms were small, hard particles that were all made of the same material but were different shapes and sizes. # Atoms were _______ in number, always moving and capable of joining together. © vm williamson This theory was ignored and forgotten for more than ______ years! Leucippus from the same time also given credit for the belief in atoms ! Why forgotten?? The eminent philosophers of the time, Aristotle and Plato, had a more respected, (and ultimately wrong) theory. Aristotle rejected atoms. He and Plato favored the belief in 4 types of matter: earth, fire, air and water. Their ideas held sway because of their eminence as philosophers. The atomos idea was buried for approximately ____ yrs. 2 Dr. Williamson’s Atoms ppt © vm williamson John Dalton ! English chemist, a quaker, employed as a teacher, discovered he was color blind to red at 26, shy, suffered from lead poisoning from drinking stout. (1766-1844) John Dalton ■ Dalton’s work eventually led to the acceptance of the idea of atoms and changed the way symbols were used. Symbols now for elements, not words Father of Modern Chemical Theory quote 3 Dr. Williamson’s Atoms ppt © vm williamson Dalton’s Theory-1803 All matter composed of atoms. Atoms are indivisible and indestructible particles. ! Atoms of the _______ element are exactly alike and differ from those of other elements. ! __________ are formed by the joining of atoms of two or more elements. ! A given compound always has the ______ number and type of atoms. ! Atoms are not created or destroyed, only ______________, in chemical reactions. ! Symbols ! Like alphabet: alphabet shorthand for sounds, symbols shorthand for elements ! Symbols are: " First letter 2 letters (uppercase, then lower) " First letter(s) of latin, greek, or german name " First Elements ! 118 made or predicted are natural except Tc (in lab only), Fr, Pm, &At (very minute, artificial samples used to get properties) _______ naturally occuring ! ______ and above are synthetic ! See objectives about which symbols and names to know ! Atoms = ! Molecule = ! 1-92 4 Dr. Williamson’s Atoms ppt © vm williamson Some Common Elements ! Al ! B ! Br ! C ! Ca ! Cl ! H ! He ! N ! O aluminum boron bromine carbon calcium chlorine hydrogen helium nitrogen oxygen ! Ag silver (argentium) gold (aurum) ! Cu copper (cuprum) ! Fe iron (ferrum) ! Hg mercury (hydragyrum) ! K potassium (kalium) ! Na sodium (natrium) ! Pb lead (plumbum) ! Sn tin (stannum) ! W tungsten (wolfram) ! Au Periodic Table of the Elements 5 Dr. Williamson’s Atoms ppt ! Understanding of atoms build slowly from indirect evidence. Lots of experiments, theories proposed and abandoned. ! Dalton proposed his Atomic Theory in 1803. ! Now: What is the nature of the atom? Was the atom homogeneous (_____ _________) throughout? © vm williamson Objective: Nuclear Evidence Joseph John Thomson (1856-1940; Nobel Prize 1906) described cathode rays. ! ■ Cathode rays are radiation produced from high voltage through partially evacuated gas tubes. ■ These rays traveled in straight lines, but were attracted to the ________ ________ of electricity & magnets, indicating the rays are ___________. ■ (SEE DEMO & overhead) 6 Dr. Williamson’s Atoms ppt © vm williamson Copyright © 1995 by Saunders College Publishing Thomson and the Cathode Ray Tube ! Results were the same with tubes containing 20 different metals as the electrode or with several different gases. ! When a small paddle wheel was placed in the path of cathode rays, the wheel was set in motion. The rays were thought to be composed of _________________ that were called “corpuscles,” later ELECTRONS ! Conclusion: All metals and gases (and probably all atoms) contain _____________. But, atoms are neutral, so atoms must contain __________charges to balance the __________ charges of the electrons. Thomson was never able to find the ________ particles. ! In 1897, Thomson measured the electrical charge to mass ratio of an electron. ! ! Which of Dalton’s theories was now abandoned?____________________ 7 Dr. Williamson’s Atoms ppt © vm williamson Electrons of atom were thought to be embedded in a positively charged ball of matter. This is the plum pudding or ________ model. Imagine the purple ovals to be electrons. ! Property of the Electron Copyright © 1995 by Saunders College Publishing Millikan’s Oil Drop Experiment ! Robert A Milliken (1868-1953; Nobel Prize 1923) did an experiment in 1909 to determine the charge of an electron, then calculated the mass. ! See overhead. Mass & Charge of an electron: ____________ g or 5.486 x 10-4AMU and _______________ Coulombs ! (No, don’t memorize the mass &charge, but know that these exist.) ! 8 Dr. Williamson’s Atoms ppt ■ A New Zealander, Ernest Rutherford (1871-1937) and his team made the plum pudding model obsolete. ■ The experiment was to direct a beam of ________________ particles at a thin piece of gold foil. Around the foil was a screen coated with zinc sulfide which gave flashes of light when the particles struck it. © vm williamson Structure of the Atom Rutherford’s Experiment ! Then read Rutherford’s words: “It was quite the most incredible event that has ever happened to me in my life. It was almost as if you fired a 15-inch shell into a piece of tissue paper and it came back and hit you!!” 9 Dr. Williamson’s Atoms ppt © vm williamson Structure of the Atom Rutherford’s Experiment For _________ particles to be deflected, there must be a heavy _____ object in the atoms of gold, with mostly open space. ! By 1911, we had the NUCLEAR atom or Rutherford model. The nucleus was thought to be small, dense (heavy), ________, and surrounded by electrons. ! If the nucleus were the size of a pea, the atom would have a mass of 250 million tons! 10 Dr. Williamson’s Atoms ppt © vm williamson Rutherford Model Copyright © 1999 by HOLT Publishing ! By 1919, protons were thought to be in nucleus. They had the opposite charge of an electron, but were much ____________. ! By 1932, James Chadwick discovered that the nucleus also contained __________ particles. Neutrons had no charge, but were slightly more massive than protons. Objective: Composition ! If all atoms are made of protons, electrons, and neutrons, what makes them different? (We know different elements have different properties.) ! Atoms of the same element have the same number of protons. The number of protons is called the ___________________. #6 = C #20 = ______ #8 = _____ 11 Dr. Williamson’s Atoms ppt ! What is the number of electrons in an aluminum atom? ______ ! The number of protons = the number of electrons in a neutral atom, this is same as the ________ _____________. ! The nucleus takes up very little space in the atom. If the nucleus is a grape, the outer edge of the atom is one mile away. See overhead. © vm williamson COMPARISONS OF ATOMIC PARTICLES ■ Particle____Actual Charge____Relative Charge Electron -1.602 x 10-19 C -1 Proton +1.602 x 10-19 C +1 Neutron none 0 ■ Particle__Actual Mass Relative to E Relative to N Electron 9.10939 x 10-28g 1 0.0005438 Proton 1.672 x 10 -24g 1836 0.9984 Neutron 1.675 x 10 -24g 1839 1 Objective: e,p,n from Notation ! The mass of an atom depends on the protons and neutrons. Protons + Neutrons = ____________. ! Nuclear Symbols: The generic form is A Z Where A =___________= ____________ and Z = ____________= _____________ X 12 Dr. Williamson’s Atoms ppt © vm williamson Atomic Notation: Nuclide Symbol Mass number Atomic number ● The A X Element symbol Z 23 atom with the symbol 11 Na has: ✻ 11 protons ✻ 11 electrons ✻ 12 neutrons ✻ mass of 23 atomic mass units ! 20Ne or just 20Ne 10 Give the number of: protons = ____________ electrons = ___________ neutrons = ____________ ! 22Ne or just 22Ne 10 protons = ______, neutrons= ______, electrons =_______ Objective: Isotopes ! 20Ne or just 20Ne or Neon-20 10 And 22 Ne or just 22Ne or Neon-22 10 are isotopes. ! Isotopes have the __________atomic number or # of p, but ________ mass numbers or # of neutrons. 13 Dr. Williamson’s Atoms ppt © vm williamson Objective: Atomic Mass Notice that on the periodic table the masses of elements are not even numbers. Atomic mass is the weighted average of the masses of naturally occurring ___________. ! There are three isotopes of carbon. The % of each in nature is: 12C = 98.892% 13C = 1.108% 14C = 2 x 10-10% ! 12C has 6 p + 6 n and has a mass of 12 AMU ! To find the atomic mass for C on the table: (______________ x 12) + (________________ x 13) + (________________ x 14) = 12.011 AMU ! Objective: Ions ! Ions are produced when an atom loses or gains electrons. ! So an ion with 20 protons, and 18 electrons would be ____________. ! An ion of copper-64 has a charge of -1. How many of each particle are present: p = ________, e = _______, & n = ____________ ! The Rutherford model of the atom was abandoned because an observation was made in the lab that his model couldn’t explain. ! This covers objectives 1-8 on Atoms 14