Electron configurations and Orbital Diagrams

What is an electron configuration What is an electron configuration? It shows how the electrons are placed around an atom. What are they used for? To show how an atom will bond and/or to explain the charge an atom has when it becomes an ion.

3s2 Number of electrons in that sublevel Energy level 3 2 1 Sublevel Letter of # of orbital Max # e- s 1 2 p 3 6 d 5 10 f 7 14

Order of filling Notice the number of columns in each section is equal to max number of e- that each sublevel can hold 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p s p d f

Example problems H – He – 1s1 Li – Be – 1s2 B – C- 1s22s1 1s22s2 Write the electron configuration for the following H – He – Li – Be – B – C- 1s1 Where do we start? How about with 1s. Then just keep moving until you have placed the correct number of electrons. 1s2 1s22s1 1s22s2 1s2 2s2 2p1 1s2 2s2 2p2

Noble Gas Short-Cut Find your element on P.T. Then move all the way to the right and up one. That is your noble gas you will use as a short-cut. Then start with what period your element is in. Let’s do potassium Long way - K – Short-cut - K – 1s2 2s2 2p6 3s2 3p6 4s1 [Ar] 4s1 Electrons in Ar = 18, therefore we only need one more electron

Valence Electrons Electrons in the outermost energy level Used to determine the charge or number of bonds O – [He] 2s2 2p4 Se – [Ar] 4s2 3d10 4p4 Both have 6 valence electrons because they are both in group 16 8 e- 2 e- 34 e- 18 e-

Val e-, bonds, and charges Gp1 gp2 gp13 gp14 gp15 gp16 gp17 gp18 1val 2val 3val 4val 5val 6val 7val 8val 1 2 3 4 3 2 1 0 1+ 2+ 3+ 4+ 3- 2- 1- 0 Octet Rule: Atoms want 8 valence electrons Duet rule: Atoms want 2 val e- (H,He, Li, Be, B)

Orbital Diagrams Adds the pairing and spin of electrons to E.C. s = 1 orbital p=3 d=5 f=7 O = [He] 2s2 2p4 You must put the max # of orbitals down, even if you do not need them (___) S P Hund’s Rule: The most stable arrangement of electrons is to place one electron in each orbital (spinning in the same direction) before pairing. Pauli’s exclusion principle: When 2 electrons are in the same orbital, they must spin in opposite directions

More examples 2 val e- V – [Ar] 4s2 3d3 Sb – [Kr] 5s2 4d10 5p3