4.4.1

• What is an approximation for the radius of an atom?

  1 x 10^-10 metres
• What are the three subatomic constituents of an atom?

  Proton, Neutron, Electron
• Where is most of the mass of an atom concentrated?

  In the nucleus
• Approximately what proportion of the total radius of an atom is the radius of the nucleus?

  1/10,000
• Describe the arrangement of protons, neutrons, and electrons in an atom.

  • Protons and neutrons are found in the nucleus.
  • Electrons are found in discrete energy levels around the nucleus.
• What type of charge does the nucleus of an atom have and why?

  Positive charge because it contains protons which have a positive charge.
• Give two ways that an atom’s electron arrangement can be changed.

  1. Absorbing electromagnetic radiation
  2. Emitting electromagnetic radiation
• How does an atom’s electron arrangement change when it absorbs EM radiation?

  Electrons move further away from the nucleus to a higher energy level.
• How does an atom’s electron arrangement change when it emits EM radiation?

  Electrons move closer to the nucleus to a lower energy level.
• How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

  The number of protons equals the number of electrons, canceling their charges.
• What do all forms of the same element have in common?

  They all have the same number of protons.
• What is the name given to the number of protons in an atom?

  Atomic Number
• What is an atom’s mass number?

  The total number of protons and neutrons in the atom.
• What is an isotope of an atom?

  An atom of an element that has a different number of neutrons but the same number of protons.
• How do atoms turn into positive ions?

  They lose one or more of their outer electrons, resulting in a positive charge.
• What may lead to a scientific model being changed or replaced?

  The discovery of new experimental evidence that doesn’t agree with the existing theory.
• How did the plum-pudding model describe the atom?

  A ball of positive charge with negatively charged electrons distributed evenly throughout it.
• Prior to the discovery of the electron, what was believed about the atom?

  The atom was believed to be indivisible.
• Which experiment led to the plum-pudding model being discarded?

  Rutherford’s alpha-scattering experiment.
• What is the name given to the currently accepted model of the atom?

  The Bohr nuclear model.
• State the conclusions of the Alpha-Scattering experiment.

  • Most of the mass of the atom is concentrated at the center in the nucleus.
  • The nucleus is positively charged.
• What reinforces a scientific theory?

  When experimental results agree with the hypothesized theoretical calculations and theories.
• What did James Chadwick’s experiments on the atom prove?

  The existence of neutrons.