Rules for Housing Electrons
Aufbau Principle: an electron occupies the lowest possible energy orbital
(see filling chart)
1.
2.
Hund’s Rule
Orbitals of equal energy are occupied by 1e before any one orbital is occupied by a 2 nd e -
All e ’s in singly occupied orbitals must have the same spin

Housing Rules
Pauli Exclusion Principle: no two e ’s in the same atom can have the same set of 4 quantum numbers
(it’s like an address for finding the e )

Drawing Orbital Diagrams



Each orbital is represented by a box or line
These can be vertical —top to bottom
-OR- These can be horizontal –left to right

1 e goes in each orbital ↑ or ↓

2 e possible in each orbital ↑↓

Lines are labeled with principle quantum number and subshell letter (s,p,d,f …)

5p
4p
3p
2p
7p
6p
8s
7s
6s
5s
4s
3s
2s
1s
Filling Diagram
6d
5d
4d
3d
5f
4f
Why do we fill this way?!? …

Relative Energies of Orbitals

Helium He:
Your Turn!
Silicon Si:

Writing Electron Configurations

Eliminates arrows and lines from orbital notation

A superscript is written on the sublevel letter to indicate the number of e ’s

Electrons enter lowest energy orbitals first
(see filling chart )

Your Turn!
He: 1s 2
Si: 1s 2 2s 2 2p 6 3s 2 3p 2
Ge:
Mg +2 :
(2 e ’s)
(14 e ’s)

Patterns in the Periodic Table

Patterns in the Periodic Table: s
The first two columns in the
P.T. (and He) are known as the “s” block

Patterns in the Periodic Table: p
Elements 5-10 and all of the elements underneath that row are known as the “p” block This block has 6 columns.

Patterns in the Periodic Table: d
Elements 21-30 and all of the elements underneath that row are known as the “d” block.
This block has 10 columns.

Patterns in the Periodic Table: f
The bottom two rows in the P.T. are known as the f block. This block has 14 columns.

Valence Electrons
Valence electrons are the outermost electrons of an atom from the s and p orbitals
Atoms with a complete shell of valence electrons (s 2 p 6 ) are considered chemically inert

Electron Configurations
Noble Gas Shorthand

For elements with completely filled shells

Substitute [noble gas] for electron configuration notation
Example:
Si: 1s 2 2s 2 2p 6 3s 2 3p 2 can be written [Ne]3s 2 3p 2

Valence Electrons
For most elements, valence electrons can be defined as those in the electronic shell of highest principle NRG level (n)
Ex. the electron configuration of phosphorus (P) is 1s 2 2s 2 2p 6 3 s 2 3 p 3 so that are 5 valence electrons (3s 2 3p 3 ),

Valence Electrons

Electron Dot Diagram
Shows the number of valence electrons
The first column of the
Periodic Table have electron configurations that end in s 1 so they have one valence electron.

Electron Dot Diagram
The second column of the Periodic Table
(and He) have electron configurations that end in s 2 so they have two valence electrons.

Electron Dot Diagram
The column starting with Boron has electron configurations that end in s 2 p 1 so they have three valence electrons.

Electron Dot Diagram
The column starting with Carbon has electron configurations that end in s 2 p 2 so they have four valence electrons.

Electron Dot Diagram
The column starting with Nitrogen has electron configurations that end in s 2 p 3 so they have five valence electrons.
And the pattern continues…

Electron Dot Diagram

Electron Configurations
Exceptions (rows 4 & 5 of P.T.)

Half filled orbitals have special stability (all electrons have the same spin)
Cr: [Ar] 4s 1 3d 5 NOT… [Ar]4s 2 3d 4

Filled orbitals have special stability
Pd: [Kr] 4d 10 NOT… [Kr] 4d 8 5s 2