Atomic structure


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Atomic structure

  2. 2. DEVELOPMENT OF ATOMIC MODEL Plum Pudding Model -discovery of electron 1897- put forward the “plum pudding” model of the atom. The atom is like a sphere with small electrons embedded in a positively charged mass J.J Thompson (1856-1940) An atom is like a miniature billiard ball 1808- suggested that matter is made of tiny particles which are indivisible and indestructible John Dalton (1766-1844) Atomic Model Atomic Structure Scientist
  3. 3. - - - - - Rutherford’s Solar System Model <ul><li>1911- shows that: </li></ul><ul><li>atom is spherical & has a centre or nucleus with a dense positive charge </li></ul><ul><li>Protons are the positively charged particles in the nucleus </li></ul><ul><li>A system of electrons rotates around the nucleus much like the planets orbiting around the sun </li></ul>Ernest Rutherford (1871-1937) Atomic Model Atomic Structure Scientist
  4. 4. <ul><li>1932- discovered that: </li></ul><ul><li>A particle in the nucleus which has no electric charge and called it neutron </li></ul><ul><li>All nuclei (except hydrogen) contain neutrons as well as protons </li></ul>James Chadwick (1891-1974) Bohr’s electrons orbiting in shells <ul><li>1913- showed that: </li></ul><ul><li>Electrons orbit in specific energy levels called shells </li></ul><ul><li>Each shell is capable of holding a certain number of electrons. </li></ul>Niels Bohr (1885-1962) Atomic Model Atomic Structure Scientist
  5. 5. <ul><li>Atomic structure of an atom </li></ul><ul><li>Atoms are made of three different types of subatomic particles called protons, neutrons and electrons </li></ul><ul><li>Protons and neutrons are found in the nucleus and they are known as nucleons </li></ul><ul><li>Nucleus is positively charged because the protons are positively charged and the neutrons are electrically neutral </li></ul><ul><li>Electrons rotate around the nucleus in a certain orbit called shells, just like planets rotate around the sun </li></ul>SUBATOMIC PARTICLES proton neutron shell electron { nucleon + +
  6. 6. THE PROPERTIES OF SUBATOMIC PARTICLES <ul><li>An atom is neutral when it has the same number of protons and electrons </li></ul>_1__ 1840 1 1 Relative mass -1 0 +1 Relative electric charge e ¯ n p Symbol Electron Neutron Proton Subatomic particles
  7. 7. PROTON NUMBER <ul><li>The number of protons in an atom of an element </li></ul>Proton number = number of protons
  8. 8. NUCLEON NUMBER <ul><li>The sum of protons and neutrons in an atom element </li></ul>Nucleon number = number of protons + number of neutrons
  9. 9. NUMBER OF NEUTRONS <ul><li>the difference between the nucleon number and the proton number </li></ul><ul><li>A neutral atom has the same number of protons and the number of electrons </li></ul><ul><li>Different elements have different numbers of protons </li></ul>Number of neutrons = nucleon number – proton number
  10. 10. <ul><li>The number of protons, electrons and neutrons in a particular atom are given in the Periodic Table by the nucleon number and proton number </li></ul><ul><li>A : proton number </li></ul><ul><li>Z :nucleon number </li></ul><ul><li>X: symbol of an element </li></ul><ul><li>The number of protons, electrons and neutrons can be determined from the nucleon number and proton number </li></ul>A X Z
  11. 11. <ul><li>Example: (a) Sulphur </li></ul><ul><li>the symbol of the element above shows that it is sulphur </li></ul><ul><li>Nucleon number = 32 </li></ul><ul><li>Proton number = 16 </li></ul><ul><li>Number of neutron = </li></ul><ul><li>So, sulphur atom has 16 protons, 16 electrons and 16 neutrons </li></ul>32 S 16 32-16 = 16
  12. 12. <ul><li>Example: (b) Aluminium </li></ul><ul><li>The symbol of the element above shows that it is aluminium </li></ul><ul><li>Nucleon number = 27 </li></ul><ul><li>Proton number = 13 </li></ul><ul><li>Number of neutron = </li></ul><ul><li>Aluminium atom has 13 protons, 13 electrons and 14 neutrons </li></ul>27 Al 13 27 – 13= 14
  13. 13. <ul><li>Example: (c) Sodium </li></ul><ul><li>Number of protons = </li></ul><ul><li>Number of neutrons </li></ul><ul><li>So, number of electrons = </li></ul>23 Na 11 11 = 23 - 11 = 12 11
  14. 14. Exercises <ul><li>What is matter? </li></ul><ul><li>What are atoms, molecules and ions? </li></ul><ul><li>How does the state of matter change with the change in temperature? </li></ul><ul><li>How does the kinetic theory of matter explain the inter-conversion of the state of matter? </li></ul><ul><li>How was the atomic model developed? </li></ul><ul><li>What are the main subatomic particles of an atom? </li></ul><ul><li>What is proton number? </li></ul><ul><li>What is nucleon number? </li></ul>