Electron Configuration

Bohr Model

picture of the 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)

Valence Electron Graphic.

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

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