Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Dr. Williamson’s Atoms ppt © vm williamson Democritus ! Atoms Dr. V.M. Williamson Atomos ! 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.” 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 ! This theory was ignored and forgotten for more than ______ years! Leucippus from the same time also given credit for the belief in atoms 400 BC # 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. 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. 1 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 Theory-1803 ■ 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 Symbols ! Like alphabet: alphabet shorthand for sounds, symbols shorthand for elements ! Symbols are: " First 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. ! letter " First 2 letters (uppercase, then lower) " First letter(s) of latin, greek, or german name 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 2 Dr. Williamson’s Atoms ppt 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) ! Au 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) Objective: Nuclear Evidence Joseph John Thomson (1856-1940; Nobel Prize 1906) described cathode rays. ! © vm williamson Periodic Table of the Elements ! 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? ■ These rays traveled in straight lines, but were attracted to the ________ ________ of electricity & magnets, indicating the rays are ___________. ■ (SEE DEMO & overhead) ■ Cathode rays are radiation produced from high voltage through partially evacuated gas tubes. 3 Dr. Williamson’s Atoms ppt © vm williamson ! 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 _____________. ! 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. Copyright © 1995 by Saunders College Publishing Thomson and the Cathode Ray Tube 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?____________________ Property of the Electron ! 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.) ! Copyright © 1995 by Saunders College Publishing Millikan’s Oil Drop Experiment 4 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 Structure of the Atom ! 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!!” 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! 5 Dr. Williamson’s Atoms ppt © vm williamson ! 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. ! 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. Rutherford Model Copyright © 1999 by HOLT Publishing 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 = _____ 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 = ____________= _____________ 6 X Dr. Williamson’s Atoms ppt © vm williamson ! 20Ne Atomic Notation: Nuclide Symbol Mass number Atomic number ● The A X Z ! 22Ne or just 20Ne Ne or just or Neon-20 22Ne 22Ne protons = ______, neutrons= ______, electrons =_______ 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 ! 10 22 or just 10 Objective: Atomic Mass Objective: Isotopes or Neon-22 10 are isotopes. ! 23 atom with the symbol 11 Na has: protons ✻ 11 electrons ✻ 12 neutrons ✻ mass of 23 atomic mass units And 20Ne Give the number of: protons = ____________ electrons = ___________ neutrons = ____________ Element symbol ✻ 11 ! 20Ne or just 10 Isotopes have the __________atomic number or # of p, but ________ mass numbers or # of neutrons. 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 7