Electron Configs & Oxidation States Mr. Shields Regents Chemistry U08 L03

Valence Electrons Recall … Electrons in the outermost principal energy level (the Valence Shell) are called VALENCE ELECTRONS The valence shell (n=4) Ex. 2-8-18- 6 This element has 6 valence electrons. What element is it?

As we move from left to right we add one electron at a time To the outermost Principal energy level – the Valence shell Main Group Valence shells Grp 1 2 13 14 15 16 17 18 1e 2e 3e 4e 5e 6e 7e 8e S Block P Block

Valence electron trends As you go down a group the number of electrons in the valence shell stays the same 2) As you go across a period (left to right) the # of e- in the valence shell of the main group elements increases one by one - This ignores the transition metals (d orbitals are filling in n-1)

Notice the e- trends in the Groups and Periods Lewis dot Structures for the atoms of groups 1-2 and 13-18 of The periodic table The Main group elements

Ions Recall that the electron configuration of the noble gases Is the extremely stable electron configuration It’s Known as the OCTET Argon’s config is 2-8-8 Potassium’s is 2-8-8-1 (why this config and not 2-8-9?) By losing 1 electron the electron config of the potassium Ion (K+) becomes the same as Argon’s (2-8-8) The Octet Configuration

Lewis dot structures of Ions Lewis Dot structures for ions look similar to the Lewis Dot Structures for atoms Except brackets and Charges are used: [ Na ]+ or just Na+ On the other hand, Br will fill it’s valence shell giving it 8 valence electrons. It’s Lewis dot structure is: [ : Br : ] -

Na is an S block element while bromine is a P block element S block elements (metals) form pos. ions by losing e- P block ions (the non-metals) form neg. ions by gaining e-. The d and f Blocks elements Are also metals Therefore they also form Positive ions Na Co Br U Ex. Co+3 or U+6

Effective Nuclear Charge Whether an atom gains or loses electrons will depend upon the Effective Nuclear Charge. For example K loses 1 e- and Cl gains 1 e- The effective Nuclear charge Is the + charge felt by The Valence electrons. Inner electrons shield Valence electrons from “Feeling” the nuclear charge Val. e- held firmly Val. e- held less firmly

Variation of nuclear charge across the Periodic Table Cations Anions Most common Oxidation nos. 4+ Always! Electrons lost vary Variation of nuclear charge across the Periodic Table

Oxidation Numbers An oxidation number represents the number of electrons an atom will typically gain or lose to achieve the octet. For example: The oxidation number of Sodium is +1 The oxidation number of Oxygen is -2 Some Atoms can have more than one oxidation number Open up your reference tables and look at the oxidation numbers. Oxidation numbers are located in the upper right. Check out various metal and non-metal oxidation nos.