Mod 2

• Atom


  Composed of electrons (e-), negatively charged particle, positively charged nucleus at the center, subdivided into two subatomic particles or nucleons called neutrons and protons

  
• Mass of neutrons (N) is approximately equal to the mass of protons (Z) and electrons (e-)

  
• The number of electrons in a stable atom is proportional to the number of protons inside the nucleus

  
• For an atom to be stable and electrically neutral, the number of electrons should be proportional to the number of protons inside the nucleus

  
• Atomic shells


  Paths where electrons orbit around the nucleus, arranged in sequence: K-shell (n=1), L-shell, M-shell, N-shell, and beyond

  
• Pauli Exclusion Principle


  Dictates the maximum number of electrons in each shell
• Atomic mass (A)


  Sum of the number of neutrons (N) and protons (Z) in the nucleus

  
• The number of protons inside the nucleus determines the nuclide/element

  
• Atomic size


  Determined by the formula: R = Ro * A^(1/3), where R is the radius in femtometer (fm) scale

  
• Actual atomic mass


  Determined by the formula: mA = A - Δm, where Δm is the mass excess derived from Einstein's E=mc^2 equation

  
• The atomic mass represented by A is an approximate mass of the nuclide, while the actual atomic mass mA accounts for the energy that binds the nucleons together

  
• Stable nuclides


  • Located on the line of stability (black squares) in the graph of number of protons vs number of neutrons
  • Nuclides above the line are unstable, proton-rich
  • Nuclides below the line are unstable, neutron-rich
  • Bi209 is the upper mass limit of the line of stability

  
• Isotopes


  Variations of an atom of the same element with the same number of protons (Z) but different numbers of neutrons (N) and atomic mass (A)
• Isotones


  Variations of an atom of different elements with the same number of neutrons (N) but different numbers of protons (Z) and atomic mass (A)

  
• Isobars


  Variations of an atom of different elements with the same atomic mass (A) but different numbers of protons (Z) and neutrons (N)

  
• Out of the 4 known forces in the universe, three of them are found in the atom: electromagnetic force, strong nuclear force, and weak nuclear force
• Electromagnetic force


  The force that keeps the electrons in orbit with the nucleus

  
• Strong nuclear force (nuclear binding force)


  The force that binds the nucleons together, preventing them from repelling each other
• Weak nuclear force


  The force that enables the transformation of protons to neutrons or neutrons to protons
• Electron binding energy


  The energy required to completely remove an electron from an atom or its shell
• Nuclear binding energy


  The energy required to separate protons and neutrons inside the nucleus