Atomic structure
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The document outlines the history of the atomic model from ancient Greek philosophers' idea of indivisible atoms to modern atomic structure. It discusses early atomic theorists like Democritus, Dalton, Thompson, Rutherford, and Bohr and how their work refined understanding of atoms. Key developments included discovering the electron and proposing nuclear and planetary models of the atom. The document then explains atomic structure, defining protons, neutrons, electrons, and their arrangement in shells according to electronic configuration and dot-and-cross diagrams.
Atomic structure
- 2. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 460 BC Democritus develops the idea of atoms he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called AATTOOMMAA (greek for indivisible)
- 3. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them AATTOOMMSS
- 4. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an EELLEECCTTRROONN
- 5. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 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. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 1910 Ernest Rutherford 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. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 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. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 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. HHIISSTTOORRYY OOFF TTHHEE AATTOOMM 1913 Niels Bohr 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 N + + N - - proton Shell electron neutron What do these particles consist of?
- 12. AATTOOMMIICC SSTTRRUUCCTTUURREE Particle proton neutron electron Charge + ve charge No charge -ve charge Mass 1 1 nil
- 13. AATTOOMMIICC SSTTRRUUCCTTUURREE Atomic number the number of protons in an atom the number of protons and neutrons in an atom HHee22 44 Atomic mass number of electrons = number of protons
- 14. AATTOOMMIICC SSTTRRUUCCTTUURREE 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. AATTOOMMIICC SSTTRRUUCCTTUURREE There are two ways to represent the atomic structure of an element or compound; 1. Electronic Configuration 2. Dot & Cross Diagrams
- 16. EELLEECCTTRROONNIICC CCOONNFFIIGGUURRAATTIIOONN With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; N Nitrogen 7 14 2 in 1st shell 5 in 2nd shell configuration = 2 , 5 2 + 5 = 7
- 17. EELLEECCTTRROONNIICC CCOONNFFIIGGUURRAATTIIOONN Write the electronic configuration for the following elements; Na 20 40 Ca O 2,8,8,2 2,8,1 Cl Si 11 23 8 17 16 35 14 28 2,6 5 B 11 a) b) c) d) e) f) 2,8,7 2,8,4 2,3
- 18. DDOOTT && CCRROOSSSS DDIIAAGGRRAAMMSS 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 X N X X X N7 X X 14
- 19. DDOOTT && CCRROOSSSS DDIIAAGGRRAAMMSS Draw the Dot & Cross diagrams for the following elements; 8 17 O Cl a) b) 16 35 X X O X X X X X X X Cl X X X X X X X X X X X X X X X X X
- 20. SSUUMMMMAARRYY 1. The Atomic Number of an atom = number of protons in the nucleus. 2. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. 3. The number of Protons = Number of Electrons. 4. Electrons orbit the nucleus in shells. 5. Each shell can only carry a set number of electrons.