Chemistry Notes 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 Most stable electron arrangement Charge Charge Bonding patterns Bonding patterns Etc. 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  1s 1 He  1s 2 Li  1s 2 2s 1 O  1s 2 2s 2 2p 4

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 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 unit they add up to 47. Remember how many electrons can go in each sublevel. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 9 s = 2 p = 6 d = 10 f = 14 Notice: the last sublevel only contains 9 (not 10) electrons

Electron Configurations Another Ex:  Another Ex:  Titanium has 22 electrons Ti: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d

Electron Configurations Here is a similar diagram for EC

Electron Configurations EC can be abbreviated  a noble gas configuration (seen below). ElementZElectron Configuration Noble Gas Configuration Scandium 211s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 [Ar] 4s 2 3d 1Ar Titanium 221s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2 [Ar] 4s 2 3d 2Ar Vanadium 231s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 [Ar] 4s 2 3d 3Ar Notice: [Ar] represents the EC of Argon

Orbital Filling Diagrams An orbital diagram give 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 Upward-pointing arrows represent electrons with +1/2 spin Downward-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

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. 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 Recall the Auf Bau Principle Write and OFD Recall Hund’s Rule Recall Hund’s Rule Recall the Pauli Exclusion Principle Recall the Pauli Exclusion Principle