The Structure of the Atom

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The Structure of an Atom

  2. 2. All matter is made up of atoms. Atoms of an element are identical. Each element has different atoms. Atoms can engage in a chemical reactions. Atoms can neither be created nor be destroyed. Atoms are indivisible. Atomic Theory John Dalton (1776-1884)
  3. 3. atom has a positively charged central part (nucleus) Electrons are distributed around nucleus Mass of an atom is concentrated at nucleus. Compared with total volume of an atom, the volume of nucleus is meager Rutherford’s Atomic Model Ernest Rutherford (1871-1937)
  4. 4. Solar system Rutherford‘s atom model Planetary model of atom
  5. 5. Bohr’s Model of the Atom Niels Bohr 1913
  6. 6. Bohr’s Model of the Atom  electrons orbit the nucleus like planets orbit the sun
  7. 7. Bohr’s Model of the Atom  electrons fills the orbits closest to the nucleus e.g. fluorine: #P = 9 #e- = 9 #N = 10 9P 10N
  8. 8.  each orbit can hold a specific maximum number of electrons Shell maximum no: of electrons 1 – K 2 – L 3 – M 4 – N Bohr’s Model of the Atom 2 8 18 32
  9. 9. Bohr’s Model Nucleus Electron Orbit Energy Levels
  10. 10. What is the structure of an atom? • Nucleus – center of the atom Home of Protons and Neutrons Has a positive charge • Proton Has a relative mass of 1 Has a positive (+) charge Determines the atomic number Found inside the nucleus
  11. 11. What is the structure of an atom? • Neutron Has no (0) charge Has a relative mass of 1 Found inside the nucleus
  12. 12. What is the structure of an atom? • Electron Has a negative (-) charge Found outside the nucleus • Rutherford atom model – electrons are around the nucleus • Bohr model – electrons are in specific energy levels called shells
  13. 13. How are p, n, e related? • No: protons = No: electrons • No: protons = atomic number • No: protons + No:neutrons = mass number • No: neutrons=mass no: – atomic no:
  14. 14. ATOMIC STRUCTUREATOMIC STRUCTURE the number of protons in an atom the number of protons and neutrons in an atom HeHe 22 44Atomic mass Atomic number number of electrons = number of protons
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