Electron Configuration

Bohr Model

• Electrons live in “shells” that revolve around the nucleus of the atom

• The first shell can hold 2 electrons

• Every subsequent shell can hold 8 electrons

• The last shell is known as the valence shell and is involved with all chemical reactions (bonds form by the sharing of electrons)

Heisenberg Uncertainty Principle

• In reality, electrons are going everywhere — we don’t know where electrons are, and if they are in neat shells

  • states that it’s near impossible to calculate both the position and velocity of a particle at the same moment in time

Suborbitals

Orbitals are clouds of probability where an electron might be found → an area where they are they may be

• but also arranged by the different levels of energy

Rules of Suborbitals

• Aufbau Principle (build up)

  • Electrons fill the lowest energy level and orbital first, and then “build” their way up

    

• Pauli Exclusion Principle

  • Each suborbital can hold a maximum of 2 electrons

  • Each electron is typically denoted with an up or a down arrow

  • A full orbital will have one up, and one down arrow

    

• Hund’s Principle

  • Each suborbital in a energy level is filled with one electron, before any other orbital is filled

  • Typically, the first electron is shown as an up arrow (↑) and the second electron with a down arrow (↓)

    • a down arrow MUST be paired with a up arrow beforehand

      • start pairing them if you run out of boxes, ensuring that all electrons are accounted for in the correct order according to Hund's rule.

Naming

• To name the electron configuration, list every energy level, every orbital, and how many electrons are in each orbital

Shorthand

• For writing the notation for longer molecules — use the noble gas method

  • Instead of writing out the full electron configuration, we can instead list the most recent noble gas, and then the following orbitals

    • 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s2 becomes…

      [Xe] 6s2