Materials and Development of Earth

• Subatomic particles

  Protons, Neutrons and electrons
• Mass number


  The number of protons and neutrons added together
• Valence shell


  The outer shell
• Atoms are neutral because they have the same number of neutrons and protons
• Atom

  • Small, dense nucleus made up of positive protons, neutral neutrons, with negative electrons, in "orbit" around nucleus
• 1904-JJ Thomson discovered the electron. This proved that there was something smaller than an atom. He developed the plum pudding model of the atom
• Plum Pudding model


  • Mass is spread out evenly throughout the atom
  • Positive charge is spread out in the same way
  • Electrons/negative charge "buried" throughout and fixed in place
  • Overall the atom had no charge
• Nuclear model


  • There is a very small nucleus in the centre of the atom, which contains most the mass and is positively charged
  • The electrons orbit the nucleus in fixed shells
• Plum pudding model

  The pudding represents the positively charged round mass, the plums represent the electrons
• 1911-Ernest Rutherford discovered that most an atom is empty space with a tiny positive nucleus. He developed the nuclear model of the atom
• 1913-Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at fixed distances (shells)
• 1920-Rutherford developed the theory that there were even smaller positive particles inside the nucleus which he called protons
• 1932-James Chadwick discovered that there were also particles in the nucleus which has no charge. He called them neutrons