2 Chemistry Timeline #1 2000 years of Alchemy B.C. 400 B.C. Demokritos and Leucippos use the term "atomos” years of Alchemy1500'sGeorg Bauer: systematic metallurgyParacelsus: medicinal application of minerals1600'sRobert Boyle:The Skeptical Chemist. Quantitative experimentation, identification ofelements1700s'Georg Stahl: Phlogiston TheoryJoseph Priestly: Discovery of oxygenAntoine Lavoisier: The role of oxygen in combustion, law of conservation ofmass, first modern chemistry textbook
3 Chemistry Timeline #21800'sJoseph Proust: The law of definite proportion (composition)John Dalton: The Atomic Theory, The law of multiple proportionsJoseph Gay-Lussac: Combining volumes of gases, existence of diatomic moleculesAmadeo Avogadro: Molar volumes of gasesJons Jakob Berzelius: Relative atomic masses, modern symbols for the elementsDmitri Mendeleyev: The periodic tableJ.J. Thomson: discovery of the electronHenri Becquerel: Discovery of radioactivity1900'sRobert Millikan: Charge and mass of the electronErnest Rutherford: Existence of the nucleus, and its relative sizeMeitner & Fermi: Sustained nuclear fissionErnest Lawrence: The cyclotron and trans-uranium elements
4 Dalton’s Atomic Theory (1808) All matter is composed of extremely small particles called atomsAtoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other propertiesJohn DaltonAtoms cannot be subdivided, created, or destroyedAtoms of different elements combine in simple whole-number ratios to form chemical compoundsIn chemical reactions, atoms are combined, separated, or rearranged
5 Modern Atomic Theory Dalton said: Several changes have been made to Dalton’s theory.Dalton said:Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other propertiesModern theory states:Atoms of an element have a characteristic average mass which is unique to that element.
6 Modern Atomic Theory #2 Dalton said: Atoms cannot be subdivided, created, or destroyedModern theory states:Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions
7 Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
8 Thomson’s Atomic Model J.J. ThomsonThomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.
9 Mass of the Electron1909 – Robert Millikan determines the mass of the electron.Mass of the electron is9.109 x kgThe oil drop apparatus
10 Conclusions from the Study of the Electron Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electronsElectrons have so little mass that atoms must contain other particles that account for most of the mass
11 Rutherford’s Gold Foil Experiment Alpha particles are helium nucleiParticles were fired at a thin sheet of gold foilParticle hits on the detecting screen (film) are recorded
12 Try it Yourself!In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?
14 Rutherford’s Findings Most of the particles passed right throughA few particles were deflectedVERY FEW were greatly deflected“Like howitzer shells bouncing off of tissue paper!”Conclusions:The nucleus is smallThe nucleus is denseThe nucleus is positively charged
15 Atomic Particles Particle Charge Mass (kg) Location Electron -1 9.109 x 10-31Electron cloudProton+11.673 x 10-27NucleusNeutron1.675 x 10-27
16 The Atomic Scale Helium-4 Most of the mass of the atom is in the nucleus (protons and neutrons)Electrons are found outside of the nucleus (the electron cloud)Most of the volume of the atom is empty spaceImage: User Yzmo Wikimedia Commons.
17 About Quarks… Protons and neutrons are NOT fundamental particles. Protons are made of two “up” quarks and one “down” quark.Neutrons are made of one “up” quark and two “down” quarks.Quarks are held together by “gluons”Images: Arpad Horvath, Wikimedia Commons.
18 IsotopesIsotopes are atoms of the same element having different masses due to varying numbers of neutrons.IsotopeProtonsElectronsNeutronsNucleusHydrogen–1(protium)1Hydrogen-2(deuterium)Hydrogen-3(tritium)2
19 Composition of the nucleus Atomic MassesAtomic mass is the average of all the naturally isotopes of that element.IsotopeSymbolComposition of the nucleus% in natureCarbon-1212C6 protons6 neutrons98.89%Carbon-1313C7 neutrons1.11%Carbon-1414C8 neutrons<0.01%Carbon =
20 Atomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.Element# of protonsAtomic # (Z)Carbon6Phosphorus15Gold79
21 Mass NumberMass number is the number of protons and neutrons in the nucleus of an isotope.Mass # = p+ + n0Nuclidep+n0e-Mass #Oxygen -10-3342- 3115188818Arsenic753375Phosphorus161531
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