PHYSICS: Atomic Structure

• What is the basic idea of the atom as described in the study material?

  The atom is a collection of smaller particles.
• What did ancient Greeks believe about matter?

  They believed matter was made up of combinations of four elements: earth, air, fire, and water.
• Who was Demokritos and what was his contribution to atomic theory?

  Demokritos was a philosopher who believed matter was made up of tiny, uncuttable pieces.
• What does the word 'atomos' mean?

  'Atomos' means uncuttable.
• What model did J J Thomson propose for the atom?

  Thomson proposed the plum pudding model.
• How did Thomson describe the structure of the atom in the plum pudding model?

  The atom is a sphere of positive charge with negatively charged electrons embedded in it.
• What evidence did Thomson use to support his plum pudding model?

  He used evidence that solids cannot be squashed and that rubbing solids together creates static charge.
• What is an electron?

  An electron is a subatomic particle with a negative charge and negligible mass relative to protons and neutrons.
• What are the key developments in the atomic model as mentioned in the study material?

  • Early ideas of matter: Four elements (earth, air, fire, water)
  • Demokritos' theory of uncuttable pieces
  • Thomson's plum pudding model
• What is the significance of the year 1897 in atomic theory?

  It is the year J J Thomson discovered the electron.
• Why did Thomson believe there must be something on the outsides of atoms?

  Because rubbing two solids together often results in static charge.
• How does the plum pudding model explain the existence of static electricity?

  It suggests that electrons can be transferred as atoms collide.
• What is the basic idea of the atom as described in the study material?

  The atom is known to be a collection of smaller particles.
• What was the purpose of Rutherford's experiment in 1905?

  To test the plum pudding model of the atom.
• Who were the two students that assisted Rutherford in his experiment?

  Hans Geiger and Ernest Marsden.
• Why was a vacuum used in Rutherford's experiment?

  To ensure that deflections were only due to collisions with the gold foil.
• What is an alpha particle composed of?

  Two protons and two neutrons.
• Why was gold chosen for Rutherford's experiment?

  Because it could be rolled out to be very thin without cracking.
• What did Rutherford conclude from the observation that most alpha particles passed straight through the foil?

  That the atom is mostly empty space.
• What did the deflection of a small number of alpha particles at large angles suggest?

  That there is a concentration of positive charge in the atom.
• What does the very small number of alpha particles coming straight back indicate about the nucleus?

  That the positive charge and mass are concentrated in a tiny volume in the atom.
• What term did Rutherford use to describe the atom after his discoveries?

  The nuclear atom.
• What is the nucleus of an atom composed of?

  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 observations from Rutherford's gold foil experiment?

  • Most alpha particles passed straight through the foil.
  • A small number were deflected at large angles.
  • A very small number bounced back.
• What are the implications of Rutherford's findings on the atomic model?

  • Atoms are mostly empty space.
  • Positive charge is concentrated in the nucleus.
  • The nucleus is very small compared to the atom.
• What is the basic idea of the atom as described in the study material?

  The atom is considered the building block of matter.
• How has the understanding of the atom changed over time?

  It has evolved from being seen as a single particle to a collection of smaller particles.
• What is the size of the atom mentioned in the study material?

  About \(1 \times 10^{-10}\) m across.
• What did Rutherford prove about the atom?

  He proved the existence of the nucleus.
• What does the nucleus contain?

  Protons and neutrons.
• What was the uncertainty scientists had after Rutherford's discovery?

  They were unsure how electrons fit into the new atomic model.
• Who revised Rutherford's model of the atom in 1913?

  Niels Bohr.
• What did Bohr suggest about electrons in his model?

  Electrons orbit the nucleus in different energy levels.
• How did Bohr explain the colors of flames produced by burning chemicals?

  He explained that the pattern of energy released by electrons is the same for every atom of that element.
• What happens to electrons when atoms absorb energy?

  Electrons are pushed up to higher energy levels.
• What occurs when electrons jump back down to lower energy levels?

  They release light of definite frequencies.
• What particle was proposed to keep the nucleus stable?

  The neutron.
• Who proved the existence of the neutron and when?

  James Chadwick proved its existence in 1932.
• What method did Chadwick use to prove the existence of the neutron?

  He used a version of Rutherford's experiment with beryllium and a paraffin block.