1. Electron Configuration & Orbital Writing
Pre AP Chemistry

2. Electron Configuration / Energy Levels
Electrons are arranged around the nucleus in specific regions called shells.
Electrons of lower energy are located near the nucleus and electrons of higher energy are in the highest shell and are called valence electrons.
Each shell is broken down into subshells or orbitals (s, p, d, f) which are three dimensional regions around the nucleus that indicate the probable location where electrons are likely to occur.
Elements located in the same group on the periodic table have their highest energy electrons arranged in the same way and that makes them chemically similar.

3. Electron Configuration
the phone number or address of an atom.
1st = energy level of the e-.
represented by rows ( Period) on the periodic table
1 = lowest, 7 = highest
2nd = shape of sub-level
4 different shapes…found on each energy level
S, P, D, F
3rd = orientation of orbital in space.
- number of electrons, each element represents 1
electron
- S has 1 orbital with a total of 2 electrons
- P has 3 orbitals with a total of 6 electrons
- D has 5 orbitals with a total of 10 electrons
- F has 7 orbitals with a total of 14 electrons

4. Single atom orbital

5. Electron Configurations
In e- configurations, you must represent (in order), the:
energy level # (electron shell), subshell orbital (s,p,d or f) and e- # for the atom.
Always read left to right, top to bottom.

6. II. Electron Arrangement in Atoms A. Electron Configurations

7. 1s1 Hydrogen letter = the orbital location
first number =the energy level.
letter = the orbital location
superscript = number of electrons

8. 1s2 Helium Electron shell (energy level) Type of subshell orbitals
Number of electrons

9. 1s22s1 Lithium Electron shell (energy level) Type of subshell orbitals
Number of electrons

10. 1s22s2 Beryllium Electron shell (energy level)
Type of subshell orbitals
Number of electrons

11. Period 2 Boron = 1s2 2s2 2p1 Carbon = 1s2 2s2 2p2
Nitrogen = 1s2 2s2 2p3
Oxygen = 1s2 2s2 2p4
Fluorine = 1s2 2s2 2p5
Neon = 1s2 2s2 2p6
Remember that the superscript numbers must equal the atomic number

12. Write out the correct e- configuration for Na (Z = 11)
1s2 2s2 2p6 3s1
Write out the correct e- configuration for Mg (Z = 12)
1s2 2s2 2p6 3s2
Write out the correct e- configuration for P (Z = 15)
1s2 2s2 2p6 3s2 3p5
‘d’ orbitals are so large that they reach into the next energy level. Therefore, the 1st ‘d’ orbital belongs to the 3rd energy level…even though we don’t see it until the 4th row of the P.T.!
Write out the correct e- configuration for Br (Z = 35)
1s2 2s2 2p6 3s2 3p5 4s2 3d10 4p5
‘f’ orbitals are so large that they reach into the next 2 energy levels. Therefore, the 1st ‘f’ orbital belongs to the 4th energy level…even though we don’t see it until the 6th row of the P.T.!

13. Heisenberg Uncertainty Principle
Impossible to know exactly where an electron is at any moment.

14. Orbital Filling- Aufbau Principle
Aufbau principle Electrons enter at the lowest energy level Some energy levels overlap into the adjacent principal energy level.

15. Orbital Filling- Pauli Exclusion Principle
Pauli exclusion principle Spectral data shows that only 2 electrons can exist in the same orbital Electrons behave as if they were spinning about their own axis When electrons occupy the same orbital – they are said to spin in opposite directions (assign +1/2 and – 1/2).

16. Orbital Filling- Hund’s Rule
Hund’s Rule Also with the principle, you must have all orbital filled with one electron before you can add the other electron with opposite spin to the orbital All elements would like to have a completely filled orbital and the maximum number of electrons that can exist in a filled orbital is eight

17. Orbital Filling

18. Electron Arrangement in Atoms Exceptional Electron Configurations
1. Filled sublevels are more stable than partial filled or half-filled sublevels.
2. But sometimes half-filled may be more stable than other configurations.
3 Example: Iron, Copper, and Chromium
1s22s22p63s23p64s23d5
1s22s22p63s23p64s13d10 This is more stable because the higher energy sublevel is completely filled.
*1s22s22p63s23p64s13d5 3d and 4s are very close together indeed in the transition series, so filled shell or half filled shell stability (Cr, 4s13d5) is enough to tip the balance. *