11a - 1901 1918 1905 1921 1913 1922 1924 1929 The birth of...

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1 The birth of quantum mechanics: A historical overview of a scientific revolution (1900-1930) 1901 1918 1905 1921 1913 1922 1924 1929 1926 1934 1927 1932 1927 1954 Who needs Quantum-mechanics??? •Why are atoms stable? •What distinguishes atoms of different chemical elements from one another (The periodic table)? •Why do atoms form chemical bonds (molecules)? •What is holding the atoms in liquids and solids together? •How do atoms, molecules and other molecular assemblies interact with light? Chemistry is the science of atoms, how they assemble to form molecules, and how these molecules assemble to form materials. The driving forces underlying the most fundamental chemical processes can only be explained by the theory of Quantum Mechanics. Understanding of the most fundamental processes underlying chemistry is based on quantum mechanics!
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2 Historical outline of the atomic theory of matter 1. 5-th century B.C: The Greek philosopher Democritus postulates the existence of atoms (“indivisibles”) as the fundamental building blocks of matter. 2. 18-th -19-th centuries: European scientists (Lavoisier, Proust, Dalton, Gay-Lussac, Avogadro) gather indirect, but rather overwhelming experimental evidence for the existence of atoms (the laws of chemical combination). 3. Late 19-th – Early 20-th centuries: Atoms are divisible! An atom consists of a positively charged, extremely small and very massive nucleus, surrounded by negatively charged and extremely light electrons. The nucleus is made of Z positively charged protons and N neutral neutrons (A=N+Z is the mass number). The electronic and protonic charges are equal, such that there are Z electrons and the atom as a whole is neutral. (Thomson, Millikan, Ratherford). Millikan’s oil drop Experiment (1906) Thomson’s Cathode Ray Tube (CRT) Experiment (1897) Cathode rays consist of particles that we now call electrons. Rutherford alpha particle Scattering (1911) (The discovery of the nucleus and “planetary” model of the atom). 11 1 / 1.759 10 em Ck g 19 31 1.602 10 9.109 10 e eC mk g ⇒= ×
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3 Scanning tunneling microscopy (STM) Bining and Rohrer – 1986 Physics Nobel prize Iron atoms on Copper (111) surface (STM electron density image). Physics at 1900… Classical mechanics Electromagnetism Newton’s Equations (1687) Maxwell’s Equations (1865) The motion of the planets, Mechanical devices, ballistics, Translational motion of atoms and molecules The motion of the electrons in atoms ??? Electromagnetic Waves (optics, X-rays, radio waves…) Oscillating charges Emit electromagnetic radiation
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4 Electromagnetic waves (Maxwell, 1865) A beam of light consists of oscillating electric and magnetic fields, which are perpendicular to each other and to the direction in which the light is propagating. 81 2.9979 10 (in vacuum) 1 c ms λλ ν ττ == = = ±± 1 1 frequency () sH z ντ = period s τ = wavelength m λ = 1 -1 =wavenumber cm νλ = ± 0 (,) c o s2 x t Ext E π ⎡⎤ ⎛⎞ =− ⎜⎟ ⎢⎥ ⎝⎠ ⎣⎦
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5 The electromagnetic spectrum Black body radiation •Every object emits radiation from its surface.
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This note was uploaded on 06/13/2009 for the course CHEM 260 taught by Professor Staff during the Spring '08 term at University of Michigan.

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11a - 1901 1918 1905 1921 1913 1922 1924 1929 The birth of...

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