1.5 more about electron arrangements in atoms

• shells can be called main energy levels
• the maximum number of electrons in each main level can be given by the formula 2n^2 where n is the number of the energy level
• main energy levels can be divided up into sublevels called s, p, d, and f
• electrons are considered to be a cloud of negative charge
• an electron fills a volume in space called its atomic orbital
• s orbital

  
• p orbitals

  
• orbitals:

  1. s
  2. p
  3. d
  4. f
• the orbital shapes represent a volume of space in which there's a 95% probability of finding an electron
• first main energy level:

  1. one s orbital
• second main energy level:

  1. one s orbital
  2. three p orbitals
• third main energy level:

  1. one s orbital
  2. three p orbitals
  3. five d orbitals
• fourth main energy levels:

  1. one s orbital
  2. three p orbitals
  3. five d orbitals
  4. seven f orbitals
• any single atomic orbital can hold a maximum of 2 electrons
• s orbitals can hold up to 2 electrons
• p orbitals can hold up to 6 electrons
• d orbitals can hold up to 10 electrons
• f electrons can hold up to 14 electrons
• electrons have a property called spin
• two electrons in the same orbital must have opposite spins
• rules for allocating electrons:

  1. atomic orbitals of lower energy are filled first
  2. atomic orbitals of the same energy fill singly before pairing starts because electrons repel each other
  3. no atomic orbital can hold more than two electrons
• the 4s orbital fills before the 3d orbital because it is of lower energy