Atomic Structure

• What is the radius of an atom?


  1 × 10^-10 metres
• What is the structure of an atom?(3)


  • A positively charged nucleus
  • With protons and neutrons
  • Surrounded by negatively charged electrons
• When do electron arrangements change in an atom? 


  When electromagnetic radiation is absorbed or emitted.
• What happens when electromagnetic radiation is absorbed?


  The electron moves to a higher energy level.
• What happens when electromagnetic radiation is emitted?


  The electron moves to a lower energy level.
• The number of protons in an atom is equal to...


  ...the number of electrons in the atom.
• Where is most of the mass in an atom concentrated?


  In the nucleus.
• What fraction of the atom is the radius of the nucleus?

  1/10,000th
• What do all atoms of the same element have in common?

  The same number of protons.
• What is the atomic number?


  The number of protons in an atom.
• What is the mass number?


  The total number of protons and neutrons in an atom.
• Top number: Mass number

  Bottom number: Atomic number
• What happens if an atom loses one or more outer electrons?


  They turn into positive ions.
• What is an isotope?

  When atoms of the same element have different numbers of neutrons.
• What may lead to a scientific model being changed/replaced?


  New experimental evidence
• Before the discovery of the electron, what were atoms thought to be?

  Tiny undivisible spheres
• What led to the plum pudding model?


  The discovery of the electron.
• What was the plum pudding model?(2)


  • A ball of positive charge
  • Embedded electrons
• What conclusion was made from the alpha scattering experiment?(2)


  • The mass of the atom is concentrated in the nucleus
  • The nucleus is positively charged
• Why did most alpha particles go through?


  The atoms are mostly empty space and the nucleus is small.
• Why were some alpha particles deflected?

  The positively charged nucleus repelled them.
• Why were some particles deflected at almost 180°?

  The nucleus contains most of the mass of the atom.
• Niels Bohr nuclear model


  Electrons orbit the nucleus at specific distances- his theoretical observations agreed with his experiments.
• What did later experiments lead to the idea of? (3)

  • The positively charged nucleus could be subdivided into a whole number of smaller particles.
  • Each particle has equal charge.
  • Protons were discovered.
• What did James Chadwick discover? 


  Neutrons
• How long after nucleus became an accepted idea were neutrons discovered?

  20 years
• What is radioactive decay?


  When unstable atomic nuclei emit radiation to become stable.
• What type of process is radioactive decay?


  Random
• What is activity?


  The rate at which a source of unstable nuclei decays.
• What is activity measured in?

  Becquerel (Bq)
• What is 1 Becquerel?

  1 decay per second
• What is count rate?


  The number of decays recorded per second BY a detector.
• What is used to monitor the activity of a radioactive source?


  Geiger counter/Geiger-Muller tube
• What are 4 ways nuclear radiation can be emitted? (4)

  1. An alpha particle (α)
  2. A beta particle (β)
  3. A gamma ray (γ)
  4. A neutron (n)
• What is an alpha particle?

  Two neutrons and protons (same as an helium nucleus).
• What is a beta particle?


  A high speed electron emitted from the nucleus?
• What happens when an electron is emitted? (3)


  
  

  • A neutron from the nucleus changed into a proton and the electron leaves.
  • Mass number doesn't change.
  • Atomic number increases by 1.
• What happens when an alpha particle is emitted?(2)


  • Mass number decreases by 4.
  • Atomic number decreases by 2.
• What is a gamma ray?


  High energy electromagnetic radiation from the nucleus.
• What happens when a gamma ray is emitted?


  No change in mass or atomic number.