Electron Configurations Chemistry Notes Electron Configurations

Electron Configurations Studying the arrangement of electrons in atoms helps one understand chemical activity. From an electron configuration you can determine: Most stable electron arrangement Charge Bonding patterns Etc.

Electron Configurations Electron Configurations: Shows the Principle Energy Levels, the sublevels and the number of electrons in those sublevels. Examples of electron configurations: H  1s1 He  1s2 Li  1s22s1 O  1s22s22p4

Electron Configurations

Electron Configurations Rule to remember when writing an electron configuration for a certain atom: Auf Bau Principle – The lowest energy levels fill first in atoms Some Energy Levels do overlap In atoms a 4s level will fill before a 3d level because the 4s sublevel has a lower energy than the 3d.

Electron Configurations Notice: the 4s is lower in energy than the 3d sublevel, therefore, it fills first.

Electron Configurations Start at the top of the arrow, go down. Once you are at the head of the arrow go to the top of the next. Repeat until you have reached the desired number of electrons. Using this diagram can help you understand how to write the correct electron configuration for each atom.

Electron Configurations EX: Ag has 47 electrons Fill sublevels until they add up to 47. Remember how many electrons can go in each sublevel. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d9 s = 2 p = 6 d = 10 f = 14 Notice: the last sublevel only contains 9 (not 10) electrons

Electron Configurations Another Ex:  Titanium has 22 electrons Ti: 1s2 2s2 2p6 3s2 3p6 4s2 3d2 2 6 10 14

Electron Configurations Here is a similar diagram for EC

Electron Configurations EC can be abbreviated  a noble gas configuration (seen below). Element Z Electron Configuration Noble Gas Configuration Scandium 21 1s2 2s2 2p6 3s2 3p6 4s2 3d1 [Ar] 4s2 3d1 Titanium 22 1s2 2s2 2p6 3s2 3p6 4s2 3d2 [Ar] 4s2 3d2 Vanadium 23 1s2 2s2 2p6 3s2 3p6 4s2 3d3 [Ar] 4s2 3d3 Notice: [Ar] represents the EC of Argon

Orbital Filling Diagrams An orbital diagram gives more detailed information than an electron configuration. Boxes or blanks are used to represent orbitals. Arrows represent electrons. Upward-pointing arrows represent electrons with +1/2 spin Downward-pointing arrows represent electrons with -1/2 spin Like EC but arrows are used instead of #’s

Orbital Filling Diagrams

Orbital Filling Diagrams Rules to remember when writing an orbital filling diagram for a certain atom: Hund’s Rule – each orbital gets one electron before any get two EX: Nitrogen  each 2p orbital gets on e- before any get 2 e-.

Orbital Filling Diagrams Hund’s Rule (cont.) Notice that the 2p electrons are shown as… rather than. This is WRONG!!!

Orbital Filling Diagrams Rules to remember when writing an orbital filling diagram for a certain atom: Pauli Exclusion Principle – electrons in the same orbital must spin opposite directions. This is why one arrow is drawn up and one is drawn down.

Orbital Filling Diagrams Examples of An Orbital Filling Diagrams

OFD and EC

Summary Be able to… Explain what EC and OFD are Write and EC Recall the Auf Bau Principle Write and OFD Recall Hund’s Rule Recall the Pauli Exclusion Principle