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

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

3. 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
1e e e e e e e e
S Block
P Block

4. 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)

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

6. 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 (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

7. 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 : ] -

8. 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

9. 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

10. 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

11. 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.