Atomic structure

• What is the radius of an atom?

  1 × 10-10 metres
• What is the radius of a typical nucleus?

  1 × 10-14 metres
• How does the radius of the nucleus compare to that of an atom?

  at least 10,000 times smaller
• Where is most of the mass in an atom concentrated?

  the nucleus
• How are electrons arranged in atoms?

  They orbit the nucleus in shells/energy levels
• What happens when an electron absorbs EM radiation?

  It becomes excited and moves to a higher energy level
• What happens when an electron emits EM radiation?

  It becomes de-excited and moves to a lower energy level
• What is the mass of a proton?

  1
• What is the mass of a neutron?

  1
• What is the mass of an electron?

  1/2000 (nearly zero)
• What is the charge of a proton?

  +1
• What is the charge of an electron?

  -1
• What is the charge of a neutron?

  0
• Where are protons found?

  In the nucleus of the atom
• Where are neutrons found?

  In the nucleus of the atom
• Where are electrons found?

  In energy levels orbiting the nucleus
• What does the atomic number tell you?

  The number of protons, which determines which element it is
• What does the mass number tell you?

  The sum of protons and neutrons in the nucleus
• How do you calculate the number of neutrons and atom has?

  mass number - atomic number
• Why do atoms have no overall charge?

  They have the same number of positive protons and negative electrons, so the charges cancel out
• Define 'ion'

  A charged particle that has either gained or lost electrons
• How can atoms turn into positive ions?

  They lose one or more outer electrons
• Define 'isotope'

  Atoms of the same element with the same number of protons and electrons but different number of neutrons
• What can lead to a scientific model being replaced?

  New experimental evidence
• Before the electron was discovered in atoms, what were atoms thought to be?

  Tiny indivisible spheres
• What discovery led to J.J Thompson's plum pudding model?

  The electron
• Describe the plum-pudding model

  A ball of positive charge with negative electrons scattered throughout it
• What were the results of the alpha scattering experiment?

  • Most particles passed straight through
  • some deflected by small angles
  • a few deflected by large angles
• What conclusion was made from the alpha scattering experiment?

  The mass of an atom was concentrated at the centre (nucleus), the nucleus was charged and most of the atom consisted of empty space
• What was the atomic model developed based on Rutherford's alpha scattering experiment?

  The early nuclear model
• Why was thin gold foil used in the alpha scattering experiment?

  It was one atom thick
• What improvements did Neil Bohr suggest?

  Electrons orbit at specific distances
• What was the first subatomic particle in the nucleus to be discovered?

  The proton
• What did James Chadwick discover?

  The neutron
• What is radioactive decay?

  The break down of unstable nuclei which emit radiation as they change to become different elements that are more stable
• Can we predict when an atom will decay?

  No, it is a random process
• Define 'activity'

  The rate at which a source (or nuclei) decays
• The units of activity

  Becquerel/Bq
• What are three different types of radiation?

  • alpha particle (a)
  • beta particle (B)
  • gamma ray (Y)
• What is an alpha particle?

  A helium nucleus which contains two neutrons and two protons