2.2.1

• Electron configuration


  How electrons are arranged in an atom, in shells and subshells
• Shells


  • Electrons are arranged in shells
  • Shells are split into subshells
• Subshells


  • s
  • p
  • d
  • f
• s subshell


  Has 1 orbital that can hold 2 electrons
• p subshell


  Has 3 orbitals that can each hold 2 electrons, so 6 electrons total
• d subshell


  Has 5 orbitals that can each hold 2 electrons, so 10 electrons total
• f subshell


  Has 7 orbitals that can each hold 2 electrons, so 14 electrons total
• Shells are numbered, with higher numbers further from the nucleus and higher in energy
• Electrons occupy orbitals singly first before pairing up, due to electron repulsion
• Electron configuration notation


  • Shell number (principal quantum number)
  • Subshell letter (s, p, d, f)
  • Number of electrons in that subshell
• Electron configuration of iron (Fe)

  • 1s2 2s2 2p6 3s2 3p6 3d6 4s2
• Electron configuration of calcium 2+ ion (Ca2+)


  • 1s2 2s2 2p6 3s2 3p6
• Noble gas notation


  Use the noble gas with the same electron configuration up to the last filled shell, then add the remaining electrons
• Electron configurations can be written in full or using noble gas notation