Shells and Orbitals

• What is the principal quantum number symbolized by?

  'n'
• What does the lowest energy shell correspond to in terms of the principal quantum number?

  n = 1
• How does the energy of electron shells change with increasing 'n'?

  Higher shells have higher energy and higher 'n'
• What is the relationship between the principal quantum number 'n' and the distance of an electron from the nucleus?

  The higher the 'n', the further from the nucleus the electron orbits
• What are sub-shells composed of?

  Orbitals
• How do orbitals in the same sub-shell compare in terms of energy?

  They have the same energy
• What is the maximum number of electrons that each orbital can hold?

  Two electrons
• What is the relationship between orbitals and sub-shells?

  • Electrons occupy orbitals.
  • An orbital can hold a maximum of two electrons.
  • A set of orbitals of the same energy is called a sub-shell.
  • Sub-shells make up different shells of electrons.
  • Different sub-shells do not have the same energy.
• Why is the concept of an orbital important in chemistry?

  It is key to understanding many chemical properties
• What are the labels for the first three types of orbitals?


  s, p, and d
• How many orbitals are in an s sub-shell?


  One s orbital
• How many orbitals are in a p sub-shell?

  Three p orbitals
• How many orbitals are in a d sub-shell?

  Five d orbitals
• What are orbitals of exactly the same energy called?

  Degenerate orbitals
• How many sub-shells does the n = 1 shell have?

  One sub-shell
• What type of sub-shell does the n = 1 shell contain?


  An s sub-shell
• How many sub-shells does the n = 2 shell have?

  Two sub-shells
• What sub-shells are present in the n = 2 shell?

  An s sub-shell and a p sub-shell
• How many sub-shells does the n = 3 shell have?

  Three sub-shells
• What sub-shells are present in the n = 3 shell?


  An s sub-shell, a p sub-shell, and a d sub-shell
• What is the order of filling for orbitals based on energy?

  • Orbitals are filled from the lowest energy to the highest energy.
  • The usual order is: s ⇒ p ⇒ d.
  • Transition metals are an anomaly: 3s ⇒ 3p ⇒ 4s ⇒ 3d.
• Why is the 4s sub-shell considered to be of lower energy than the 3d sub-shell in transition metals?

  Because of the unique filling order in transition metals
• What are electron shells?

  Regions around the nucleus for electrons
• How are electron shells divided?

  Into subshells: s, p, d, and f
• What are orbitals?

  Regions within subshells for electrons
• How many orbitals are in each subshell?

  • s subshell: 1 orbital (2 electrons max)
  • p subshell: 3 orbitals (6 electrons max)
  • d subshell: 5 orbitals (10 electrons max)
  • f subshell: 7 orbitals (14 electrons max)
• What is the shape of the s orbital?

  Spherical in shape
• What is the shape of the p orbital?

  Dumbbell-shaped and oriented along axes
• What is the Aufbau principle?

  Electrons fill orbitals in order of energy
• What is Hund’s rule?

  Electrons fill degenerate orbitals singly first
• What is the Pauli exclusion principle?

  No two electrons can have the same quantum numbers
• How is electron configuration written?

  • List subshells in order of filling
  • Use superscripts for number of electrons
  • Example: Oxygen: 1s² 2s² 2p⁴
• What is the electron configuration of sodium (Na)?

  1s² 2s² 2p⁶ 3s¹
• What is the shorthand notation for electron configuration?

  Use noble gas in brackets, then remaining configuration
• How does the electron configuration of ions differ from neutral atoms?

  Electrons are removed or added from highest energy orbital
• Why does the 4s subshell fill before the 3d subshell?

  4s is slightly lower in energy than 3d
• What is the electron configuration of chromium (Cr)?

  1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹
• Why is the electron configuration of chromium unusual?

  It promotes one 4s electron to 3d for stability
• What is the electron configuration of copper (Cu)?

  1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹
• Why is the electron configuration of copper unusual?

  It promotes one 4s electron to 3d for stability