Atomic models through time

• What are the three main subatomic particles that make up an atom?

  Protons, neutrons, and electrons
• What happens when the number of neutrons in an atom changes?

  It becomes an isotope
• What occurs when the number of electrons in an atom changes?

  It becomes an ion
• What were the four elements believed to make up matter in ancient Greece?

  • Earth
  • Air
  • Fire
  • Water
• What was Demokritos' contribution to the understanding of matter?

  He proposed that matter is made up of tiny, uncuttable pieces called atoms
• What does the word 'atom' mean?

  'Uncuttable'
• Who discovered the electron and in what year?

  J J Thomson in 1897
• What is the plum pudding model of the atom?

  It describes the atom as a sphere of positive charge with negatively charged electrons embedded in it
• What evidence supported the plum pudding model at the time?

  Solids cannot be squashed, suggesting atoms must be solid throughout
• What experiment did Ernest Rutherford conduct in 1905?

  He directed a beam of alpha particles at thin gold leaf
• What was the purpose of using a vacuum in Rutherford's experiment?

  To ensure any deflection of alpha particles was due to collisions with the gold foil
• What were the surprising results of Rutherford's gold foil experiment?

  Most alpha particles passed through, some were deflected at large angles, and a few bounced back
• What conclusion did Rutherford draw from his experiment?

  The atom is mostly empty space with a concentrated positive charge in the nucleus
• What is the nucleus of an atom?

  The central part of an atom containing protons and neutrons
• How does the size of the nucleus compare to the size of the atom?

  The nucleus is about 1/10,000th the size of the atom
• What are the key findings of Rutherford's experiment regarding the structure of the atom?

  • Most of the atom is empty space
  • Positive charge is concentrated in the nucleus
  • Electrons surround the nucleus