Electron Configuration

1. Electron Configuration Chapter 4 Quantum numbers, describe the orbitals in which electrons can be found.

2. Bohr was wrong!! • Electrons spend time around the nucleus but NOT in nice neat circular orbits.

3. Where are the electrons? • We cannot know exactly where the electrons are. • We can only know with some degree of certainty where it is. • Quantum numbers describe where the electron may be found. • Quantum numbers are the electrons “address”.

4. Dual nature of light and matter • Energy travels in packets of energy, sort of like steps. • When an electron is excited to a higher energy level, it emits light when it returns to its original orbit. • Law of Conservation of Energy.

6. principle quantum number (n) • Describes the size of the orbital. • Referred to as the energy level.

7. The angular quantum number (l) • (l) describes the shape of the orbital. • Spherical , s, (l = 0) • Polar, p. (l = 1) • Cloverleaf ,d, (l = 2) • They can even take on more complex shapes as the value of the angular quantum number becomes larger.

9. magnetic quantum number • Magnetic quantum number (m) • Describes the orientation in space of a particular orbital. X,Y, Z axis • Named magnetic quantum number because the effect of different orientations of orbitals was first observed in the presence of a magnetic field.

10. Spin • Each orbital shape may hold two electrons. • These two electrons have opposite spins. • Designated as + ½ & - ½

11. Da Rules • The principle Quantum Number is an integer greater than or equal to 1. • The angular quantum number (l) can be any integer between 0 and n - 1. If n = 3, for example, l can be either 0, 1, or 2. • The magnetic quantum number (m) can be any integer between -l and +l. If l = 2, m can be either -2, -1, 0, +1, or +2. • Spin is + ½ & - ½

12. Shells and Subshells of Orbitals • Orbitals that have the same value of the principle quantum number form a shell. Orbitals within a shell are divided into subshells that have the same value of the angular quantum number. Chemists describe the shell and subshell in which an orbital belongs with a two-character code such as 2p or 4f. The first character indicates the shell (n = 2 or n = 4).

13. Shells and Subshells of Orbitals • The second character identifies the subshell. By convention, the following lowercase letters are used to indicate different subshells.

15. The d orbitals

16. H: 1s1 A hydrogen atom has only one electron. The lowest energy orbital is the 1s orbital. This is indicated by writing a superscript "1" after the symbol for the orbital. Electron Configuration

17. He: 1s2 Li: 1s2 2s1 Be: 1s2 2s2 B: 1s2 2s2 2p1 C: ???????? C: 1s2 2s2 2p2 Each electron is added to the lowest energy orbital available. Up to two electrons may be added to each orbital. Aufbau principle

18. But: • After all not all the orbitals are filled in Energy Level order!!

20. Hund's rules can be summarized as follows. • One electron is added to each of the degenerate orbitals in a subshell before two electrons are added to any orbital in the subshell. • Electrons are added to a subshell with the same value of the spin quantum number until each orbital in the subshell has at least one electron. • Filling the Bus!

21. Pauli Exclusion Principle • No two electron in an atom may have the same set of quantum numbers. • This is Pauli. Don’t Mess with Pauli!