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ATOMIC STRUCTURE

ATOMIC STRUCTURE. HISTORY OF THE ATOM. Democritus develops the idea of atoms. 460 BC. he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called. ATOMA ( greek for indivisible ). HISTORY OF THE ATOM. John Dalton. 1808.

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ATOMIC STRUCTURE

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  1. ATOMIC STRUCTURE

  2. HISTORY OF THE ATOM Democritus develops the idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible)

  3. HISTORY OF THE ATOM John Dalton 1808 suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

  4. HISTORY OF THE ATOM Joseph John Thompson 1898 found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

  5. HISTORY OF THE ATOM 1904 Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding. PLUM PUDDING MODEL

  6. HISTORY OF THE ATOM Ernest Rutherford 1910 oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit

  7. HISTORY OF THE ATOM gold foil helium nuclei helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.

  8. HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.

  9. HISTORY OF THE ATOM Niels Bohr 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

  10. Bohr’s Atom electrons in orbits nucleus

  11. HELIUM ATOM Shell proton N + - + N - neutron electron What do these particles consist of?

  12. ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil

  13. ATOMIC STRUCTURE He 2 Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom number of electrons = number of protons

  14. ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. • first shell a maximum of 2 electrons • second shell a maximum of 8 electrons • third shell a maximum of 8 electrons

  15. ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1. Electronic Configuration 2. Dot & Cross Diagrams

  16. ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; Nitrogen configuration = 2 , 5 7 2 in 1st shell 5 in 2nd shell N 2+5 = 7 14

  17. ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; 20 11 8 Na O Ca a) b) c) 16 23 40 2,8,8,2 2,8,1 2,6 17 14 5 Cl Si B d) e) f) 11 35 28 2,8,7 2,8,4 2,3

  18. DOT & CROSS DIAGRAMS With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X Nitrogen N 7 X X N X X 14 X X

  19. DOT & CROSS DIAGRAMS Draw the Dot & Cross diagrams for the following elements; X 8 17 X O Cl a) b) X 35 X 16 X X X X X Cl X X X X X X X O X X X X X X X X X X

  20. SUMMARY • The Atomic Number of an atom = number of • protons in the nucleus. • The Atomic Mass of an atom = number of • Protons + Neutrons in the nucleus. • The number of Protons = Number of Electrons. • Electrons orbit the nucleus in shells. • Each shell can only carry a set number of electrons.

  21. Bohr Model (1913) • Was attempting to explain line spectra • Used a combination of classical and quantum physics • Treated only H atom (one electron system)

  22. The Bohr model consists of four principles: 1) Electrons assume only certain orbits around the nucleus. These orbits are stable and called "stationary" orbits. 2) Each orbit has an energy associated with it. For example the orbit closest to the nucleus has an energy E1, the next closest E2 and so on. 3) Light is emitted when an electron jumps from a higher orbit to a lower orbit and absorbed when it jumps from a lower to higher orbit. 4) The energy and frequency of light emitted or absorbed is given by the difference between the two orbit energies, e.g.,

  23. Quantum mechanics- the structure of atom

  24. Book References • Advanced Inorganic Chemistry • - SatyaPrakashTuli, Basu, Madan • Introduction to Modern Inorganic Chemistry • S. Z. Haider • Organic Chemistry • – R. N. Boyd • Advanced Organic Chemistry • – B.S Bahl, ArunBhal

  25. Next Lecture • Bohr Model and Quantum Theory • Radius of orbit • Energy of orbit • Quantum Numbers and Atomic Orbitals • Ionization Energy • De Broglie Postulate • Heisenberg Uncertainty Principle • Shapes of Atomic Orbitals

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