Electron Configuration A detailed way of showing the order in which electrons fill in around the nucleus

Electron Configuration Symbols # of e- in sub level Electron Configuration Symbols 1s 2 Energy Level Sub Level (s, p, d, f )

We must follow 3 rules… Aufbau priciple Electrons occupy energy levels with lowest energy first.

Pauli exclusion principle If 2 electrons occupy the same energy level they must have opposite spins.

Hund’s rule… Electrons that occupy orbitals of the same energy will have the maximum number of electrons with the same spin. 2p

To start we will use orbital filling diagrams to help us with electron configurations…. Example Boron- has 5 electrons

Periodic table arrangement 22/09/99 the quantum theory helps to explain the structure of the periodic table. n - 1 indicates that the d subshell in period 4 actually starts at 3 (4 - 1 = 3).

Order of Electron Subshell Filling: It does not go “in order” 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f14 6s2 6p6 6d10 7s2 7p6 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6

Electron Configurations Element Configuration H Z=1 1s1 He Z=2 1s2 Li Z=3 1s22s1 Be Z=4 1s22s2 B Z=5 1s22s22p1 C Z=6 1s22s22p2 N Z=7 1s22s22p3 O Z=8 1s22s22p4 F Z=9 1s22s22p5 Ne Z=10 1s22s22p6 (2p is now full) Na Z=11 1s22s22p63s1 Cl Z=17 1s22s22p63s23p5 K Z=19 1s22s22p63s23p64s1 Sc Z=21 1s22s22p63s23p64s23d1 Fe Z=26 1s22s22p63s23p64s23d6 Br Z=35 1s22s22p63s23p64s23d104p5 Note that all the numbers in the electron configuration add up to the atomic number for that element. Ex: for Ne (Z=10), 2+2+6 = 10

Electron Configurations In the previous slide you will see arrows showing you the direction of the you follow the pattern to fill your electrons. The arrow points at the next highest orbital. There is also an abbreviated form in which you put the closed noble gas (element on the far right) to the top of the element you are talking about in brackets and then finish the electron configuration from there. Example: Aluminum: [Ne] 3s2 3p1