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A brief history of atomic structure

A brief history of atomic structure. Advanced Higher Chemistry Unit 1. Atomic Theory of matter. British Chemist John Dalton (1766-1844) laid the foundations of modern atomic theory by proposing the idea of atoms.

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A brief history of atomic structure

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  1. A brief history of atomic structure Advanced Higher Chemistry Unit 1

  2. Atomic Theory of matter • British Chemist John Dalton (1766-1844) laid the foundations of modern atomic theory by proposing the idea of atoms. • At the end of the 19th century chemists had discovered that atoms themselves were made up of smaller particles.

  3. Discovery of electrons • British physicist J. J. Thompson began experiments on the discharge of electricity through gases and discovered the electron. ANODE CATHODE VACCUM

  4. Discovery of the nucleus • In 1911 British Physicist Ernst Rutherford performed the alpha particle scattering experiment • Gold foil was bombarded with alpha radiation from a radioactive substance • Concluded mass of an atom was concentrated in a centre, which was also positively charged

  5. An early structure for the atom

  6. Quantization of energy • When heated, solids emit light. • Max Planck discovered that the atoms of a solid vibrate with energy of a definite frequency, f, depending on the solid. • The energy of this light is given by E = nhf, where h is Planck’s constant, 6.63 x 10-34 and n = 1, 2, 3,... • This means that the energies of a vibrating atom must take the form hf, 2hf, 3hf etc. • In this way thee energy said to be quantised – it cannot change smoothly from one value to another, only in whole units at a time.

  7. In 1900, Albert Einstein had proposed that instead of being thought of as a continuous wave, light could also be thought of as particles – “packets” of light – PHOTONS. • Based on the theories of Einstein and Planck, Danish scientist Niels Bohr proposed a model of electronic structure to explain the results of atomic spectra.

  8. Hot gases emit light, in the form of a line spectrum Hydrogen Link to Periodic Table of Spectra

  9. Bohr’s model of the atom 4 Ene r gy 3 1 2 3 2 1 ENERGY LEVELS (SHELLS) • An electron can only have specific energy values in an atom, ENERGY LEVELS • An electron can change energy only by going from one energy level to another

  10. E1 E2 Explaining emission spectra One photon, hf • An electron in an excited state can fall down an energy level, emitting a photon • Energy of emitted photon = hf = Ei - Ef • This will produce an emission spectrum

  11. Transitions in a Hydrogen Atom

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