Lesson 3: Orbital Diagrams

• Ways to represent electrons

  • Quantum numbers
  • Electron configurations
  • Orbital diagrams
• Electron configuration


  Shows the number and arrangement of electrons in an atom's orbitals
• Orbital energies for H atom

  • All energy levels with the same n have the same energy
  • Atoms with multiple electrons have electron-electron interactions that change the relative orbital energies
• Ground state

  Lowest energy state, most stable
• Pauli Exclusion Principle

  • Only 2 electrons of opposite spin (ms = +1/2, ms = -1/2) can occupy any one orbital
• Filling orbitals

  1. Aufbau principle: electrons fill orbitals starting at the lowest available energy orbital before filling higher energy orbitals. only move to the next orbital when the lowest energy orbital is full

  2. Hund's rule: Lowest energy state has the maximum number of unpaired electrons allowed. place 1 up spin electron in each subshell before pairing them with a down spin electron
• Block elements

  • S-block: groups 1 and 2, represented as ns1 and ns2
  • P-block: groups 13 to 18, represented as ns2np?
  • D-block: transition metals as well as group 12, represented as ns2(n-1)d?
  • F-block: inner transition metals, predictions are difficult because there are 7 f orbitals
• electrons have repulsive forces, therefore, if there are more electrons in an orbital, there will be more repulsive forces
• ground state: electrons are at its lowest energy state
• electrons and nucleus have forces that attract each other, but electrons have a shielding force that prevents them from colliding into the nucleus
• Explain why this one is wrong: it breaks the Pauli Exclusion Principle because the 1st subshell of 2p5 has 2 electrons that are spinning in the same direction. This is not allowed because 2 electrons cannot have the same quantum numbers.