Atomic structure

• What experiment is used to work out the nuclear model of atomic structure?

  The alpha scattering experiment
• What did ancient Greeks believe about atoms?

  Atoms are tiny spheres that can't be divided
• Why was the discovery of electrons significant?

  It showed atoms have an internal structure
• What model did scientists propose after discovering electrons?

  The plum pudding model
• What does the plum pudding model suggest about atoms?

  Atoms are a ball of positive charge with electrons
• What material did scientists use for the alpha scattering experiment?

  Gold foil
• Why was gold chosen for the alpha scattering experiment?

  It can be hammered into very thin foil
• What are alpha particles?

  Particles with a positive charge
• What did scientists observe about most alpha particles in the experiment?

  They passed straight through the gold foil
• What did the deflection of some alpha particles indicate?

  The center of the atom has a positive charge
• What does it mean if alpha particles bounce straight back?

  The mass of the atom is concentrated in the nucleus
• What is the central part of an atom called?

  The nucleus
• What happens when an alpha particle collides directly with the nucleus?

  It bounces back in the original direction
• What model replaced the plum pudding model?

  The nuclear model
• What did Neil Bohr propose about electrons?

  Electrons orbit the nucleus at specific distances
• What are the orbits of electrons called?

  Energy levels or shells
• What particles were discovered in the nucleus years later?

  Protons and neutrons
• What is the charge of neutrons?

  They are neutral
• What are the key components of the nuclear model of atomic structure?

  • Atoms are mostly empty space
  • Central nucleus contains positive charge
  • Nucleus holds most of the atom's mass
  • Electrons orbit the nucleus in energy levels
• What are the historical developments in atomic theory?

  1. Ancient Greeks: Atoms as indivisible spheres
  2. Discovery of electrons in 1897
  3. Plum pudding model proposed
  4. Alpha scattering experiment conducted
  5. Nuclear model established
  6. Discovery of protons and neutrons
• What conclusions were drawn from the alpha scattering experiment?

  • Atoms are mainly empty space
  • Positive charge is concentrated in the nucleus
  • Mass of the atom is in the nucleus
• What is the radius of an atom?

  $3 \times 10^{-10} \text{ m}$
• How does the radius of the nucleus compare to the radius of the atom?

  It is less than 1/10,000 of the atom's radius
• What particles are contained in the nucleus?

  Protons and neutrons
• What charge does the nucleus have?

  Positive charge
• What surrounds the nucleus in an atom?

  Electrons in energy levels
• How does the energy of electrons change with distance from the nucleus?

  Further energy levels have higher energy
• What happens when an atom absorbs electromagnetic radiation?

  An electron moves to a higher energy level
• What occurs when the electron returns to a lower energy level?

  The atom emits electromagnetic radiation
• What are isotopes?

  Atoms of the same element with different neutrons
• What do alpha particles consist of?

  2 protons and 2 neutrons
• What is a beta particle?

  An electron ejected from the nucleus
• What are gamma rays?

  A type of electromagnetic radiation
• How far can alpha particles travel in air?

  About 5 cm
• How far can beta particles travel in air?

  About 15 cm
• How far can gamma radiation travel in air?

  Several metres
• What stops alpha particles?

  A single sheet of paper
• What stops beta particles?

  A few millimetres of aluminium
• What stops gamma radiation?

  Several centimetres of lead
• What is ionising power?

  Radiation collides with atoms, causing ion formation