Atomic Structure You should be able to: Discuss the development of the atom from earliest atomic theory to modern day theory of the atom Explain how experimental observations and inferences by Rutherford and Bohr contributed to the development of the planetary model of the hydrogen atom. Use appropriate terminology related to atomic structure including orbital, emission spectrum, energy level, photon etc Describe the electron configurations of elements, using the concept of energy levels in shells and subshells, the Pauli exclusion principle, Hunds rule and the aufbau principle.
Draw energy level diagrams for element and ions. Write the electron configuration of any element or ion and to relate its electron configuration to its position in the periodic table. Know what each of the four quantum numbers n, l, m, and m s represents. Identify the four quantum numbers for an electron in an atom. Identify the number and location of the valence electrons in an atom. Identify the characteristic properties of elements in each of the s,p and d blocks of the periodic table.
Greek Model Greek philosopher – thought experiments Idea of atomos Atomos = indivisible Tear up a piece of matter until you reach the atomos. Democrituss model of atom Democritus ( 400 B.C.) To understand the very large, we must understand the very small. Nothing exists but atoms and space, all else is opinion.
Alchemy (500 – 1400 A.D.).............. GOLDSILVERCOPPER IRONSAND Alchemical symbols for substances… transmutation: changing one substance into another In ordinary chemistry, we cannot transmute elements.
Contributions of alchemists: Information about elements - the elements mercury, sulfur, and antimony were discovered - properties of some elements Develop lab apparatus / procedures / experimental techniques - alchemists learned how to prepare acids. - developed several alloys - new glassware
Daltons Atomic Theory 1805 1.All matter consists of tiny particles called atoms. 2.Atoms cannot be subdivided, created or destroyed. 3.All atoms of an element are identical. 4.Atoms of different elements are different from each other. 5.Atoms of different types combine is specific ratios to form compounds. Billiard Ball Model
Radioactivity (1896) 1. rays or particles produced by unstable nuclei a. Alpha Rays – helium nucleus b. Beta Part. – high speed electron c. Gamma ray – high energy x-ray 2. Discovered by Becquerel – exposed photographic film 3. Further work by Curies Antoine-Henri Becquerel (1852 - 1908)
Thomsons Experiment 1897 + - vacuum tube metal disks voltage source
Thomsons Experiment + - vacuum tube metal disks voltage source
Thomsons Experiment + - voltage source OFF ON Passing an electric current makes a beam appear to move from the negative to the positive end
Thomsons Experiment + - voltage source ON + - By adding an electric field… he found that the moving pieces were negative.
Thomsons Raisin Bun Model 1897 Using cathode ray tubes, he was able to deflect cathode rays with an electric field. The rays are bent towards the positive pole, indicating that cathode ray particles are negatively charged. (electrons) Atom is a + sphere with – electrons embedded.
Thomsons Plum-Pudding or Raisin Bun Model Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56
Ernest Rutherford (1871-1937) Planetary Model of the Atom Learned physics in J.J. Thomson lab. Noticed that alpha particles were sometimes deflected by something in the air. Gold-foil experiment Rutherford PAPE R Rutherford PAPE R Animation by Raymond Chang Animation by Raymond Chang – All rights reserved.
Rutherfords Apparatus beam of alpha particles radioactive substance gold foil circular ZnS - coated fluorescent screen Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 120 Rutherford received the 1908 Nobel Prize in Chemistry for his pioneering work in nuclear chemistry.1908 Nobel Prize in Chemistry
Results of foil experiment if plum-pudding had been correct. Electrons scattered throughout positive charges Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57 + + + + + + + + - - - - - - - -
Rutherfords Gold Foil Experiment (1909) Revised Theory
Interpreting the Observed Deflections Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 120.............. gold foil deflected particle undeflected particles.. beam of alpha particles.
Rutherfords Gold-Leaf Experiment Conclusions: Atom is mostly empty space Atom has a very small, dense, positively charged core. (nucleus) Electrons float around nucleus Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 120
Evidence for Particles In 1886, Goldstein, using equipment similar to cathode ray tube, discovered particles with charge equal and opposite to that of electron, but much larger mass. Rutherford later (1911) found these particles to be identical to hydrogen atoms minus one electron - named these particles protons Chadwick (1932) discovered particles with similar mass to proton but zero charge. - discovered neutrons
An unsatisfactory model for the hydrogen atom According to classical physics, light should be emitted as the electron circles the nucleus. A loss of energy would cause the electron to be drawn closer to the nucleus and eventually spiral into it. Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 294
Bohrs Model Nucleus Electron Orbit Energy Levels
Niels Bohr (1913) 1.e - can only occupy certain regions of space (orbits) 2.e - only have specific (quantized) energy values in an atom (energy levels) 3.e - can move from one orbit to another by absorbing or emitting energy, giving rise to characteristic spectra. Bohrs model could not explain the spectra of atoms heavier than hydrogen.
Bohr Model of Atom The Bohr model of the atom, like many ideas in the history of science, was at first prompted by and later partially disproved by experimentation. http://en.wikipedia.org/wiki/Category:Chemistry Increasing energy of orbits n = 1 n = 2 n = 3 A photon is emitted with energy E = hf e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-