Lesson 5: QUANTUM NUMBERS

• Quantum numbers


  Used to describe the location and motion of electrons in an atom

  
• The location of the electrons in the quantum mechanical model of the atom is called an electron cloud

  
• Electron cloud


  The region of space within which there is 90% probability of finding an electron

  
• To completely describe an electron in an atom, four quantum numbers are needed

  
• Quantum mechanical model


  A radical departure from Bohr model, proposed by Neils Bohr
• Four quantum numbers


  • Principal Quantum Number (n)
  • Angular Momentum Quantum Number (l)
  • Magnetic Quantum Number (ml)
  • Spin Quantum Number (ms)

  
• Principal Quantum Number (n)


  The main energy level or shell occupied by the electron, represented by whole numbers (1, 2, 3, etc.)

  
• Angular Momentum Quantum Number (l)


  The number that further divides the shells into subshells, tells the shape or orbital of the electron

  
• Orbitals


  s orbital (l=0), p orbital (l=1), d orbital (l=2), f orbital (l=3)
• The possible values for ml depend on the angular momentum quantum number (l), it could be -l to +l

  
• Spin Quantum Number (ms)

  Tells the spin of the electron on its axis, +1/2 for clockwise, -1/2 for counterclockwise

  
• Electron configuration


  Describes how electrons are distributed in their atomic orbitals

  
• Aufbau Principle


  An electron occupies orbitals in order from lowest energy to highest
• Pauli Exclusion Principle


  No two electrons in an atom can have the same set of four quantum numbers
• Hund's Rule


  Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and each single electron must have the same spin

  
• Orbital filling diagram


  A visual representation of the arrangement of all electrons in a particular atom, with individual orbitals shown as squares