8.5 – Valence Electrons 1s2 2s22p6 3s23p6 4s1 When atoms undergo a chemical reaction, only the outermost e- are involved (furthest from nucleus and highest in energy  valence electrons

Electron Configuration Valence electrons are the ones in the s and p subshells beyond the noble gas core, and partially filled d and f subshells If all subshells are completely full in a atom (i.e. noble gas) then there are no valence electrons Atom Electron Configuration # Valence e- Al Ga Pb Xe [Ne] 3s23p1 3 [Ar] 4s23d104p1 3 [Xe] 6s24f145d106p2 4 [Kr] 5s24d105p6 0 or 8

Can you see a pattern for counting valence electrons on the periodic table? 1 2 3 4 5 6 7 0 or 8 varied

8.6 – Electron Configuration of Ions 1s22s22p4 What’s changed from O to O2-? If you had to guess where to stick the two electrons, where would they go? O2-: ??

1s22s22p4 + 2e-  1s22s22p6 1s22s22p63s23p4 + 2e-  1s22s22p63s23p6 For negative ions, add the extra electron(s) where you left off in the neutral atom Example: Write the electron configuration for the following negative ions: a) O2- 1s22s22p4 + 2e-  1s22s22p6 b) S2- 1s22s22p63s23p4 + 2e-  1s22s22p63s23p6 c) Br- [Ar]4s23d104p5 + 1e-  [Ar]4s23d104p6

Sn: Sn2+: ?? 1s22s22p63s23p64s23d104p65s24d105p2 highest n p s d For positive ions, Electrons in subshells with the _______________ value and highest energy are moved first Electrons are removed from the ____ -subshell first, then ____, and then _____-subshells highest n p s d Sn: 1s22s22p63s23p64s23d104p65s24d105p2 What has changed between Sn and Sn2+? Before I ask you if you had to guess where the electrons will be removed from, where are they most definitely not removed from? Which subshells are not involved in creating a positive ion? Sn2+: ??

highest n p s d [Kr]5s24d105p2 - 2e-  [Kr]5s24d10 [Kr]5s24d105p2 For positive ions, Electrons in subshells with the _______________ value and highest energy are moved first Electrons are removed from the ____ -subshell first, then ____, and then _____-subshells highest n p s d a) Sn2+ [Kr]5s24d105p2 - 2e-  [Kr]5s24d10 b) Sn4+ What has changed between Sn and Sn2+? Before I ask you if you had to guess where the electrons will be removed from, where are they most definitely not removed from? Which subshells are not involved in creating a positive ion? [Kr]5s24d105p2 - 4e-  [Kr]4d10 c) V2+ [Ar]4s23d3 - 2e-  [Ar]3d3

noble gas isoelectronic Ne Ar Kr Example: Write the electron configuration for the following ions: Neutral Atom Ion O2- S2- Br- Sn2+ Sn4+ V2+ 1s22s22p4 1s22s22p63s23p4 [Ar]4s23d104p5 [Kr]5s24d105p2 [Ar]4s23d3 + 2e- → + e- → - 2e- → - 4e- → 1s22s22p6 1s22s22p63s23p6 [Ar]4s23d104p6 [Kr]5s24d10 [Kr]4d10 [Ar]3d3 Ne Ar Kr When an atom becomes an ion, its electron configuration sometimes becomes the same as the configuration for the nearest ___________________. When two atoms have the same electron configuration, they are said to be _____________________. noble gas isoelectronic

Practice: Which of the following is isoelectronic with krypton when ionized? Cl Zn Br Ca Sr Se I

Consider this: If two atoms have the same electronic configuration, are they the same element? NO!!! It is the #p that determines the element.