1. Electron Configuration Chemistry Mrs. Stoops

2. The Rules Hund’s rule – each orbital will fill up with one electron before doubling up – like a bus, people will fill empty seats before sitting with someone Aufbau principle – electrons will occupy the lowest energy level possible – like people, we will do minimal work (not work ahead) or like a ladder, we start at the bottom and work up.

3. Electron Configurations N = 1s 2 2s 2 2p 3 List all the elements passed through starting from hydrogen down to the element you are looking for Adding up the exponents will equal the atomic number Uses the first two quantum number (row or section letter) Co = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7 ** still subtract for rows Pt = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 8 PT

5. Exceptions EXCEPTION group: Cr column and Cu column: Cr, Mo, W, Sg, Cu, Ag, Au, Uuu(Rg) Applies to both orbital and e configurations These elements are “thieves” they steal an electron from the closest “s” section to fill or half-fill the “d” section for stability. Cr = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 PT

6. Back to: E config exceptions Short-cut orbitals