Electron Configurations

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

(it’s like an address for finding the e-) 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…)

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

Relative Energies of Orbitals

Your Turn! Helium He: 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: 1s2 (2 e- ’s) Si: 1s22s22p63s23p2 (14 e- ’s) Ge: Mg+2 :

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 (s2p6) are considered chemically inert

Electron Configurations Noble Gas Shorthand For elements with completely filled shells Substitute [noble gas] for electron configuration notation Example: Si: 1s22s22p63s23p2 can be written [Ne]3s23p2

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 1s2 2s2 2p6 3s2 3p3 so that are 5 valence electrons (3s2 3p3),

Valence Electrons

Electron Dot Diagram Shows the number of valence electrons The first column of the Periodic Table have electron configurations that end in s1 so they have one valence electron.

Electron Dot Diagram The second column of the Periodic Table (and He) have electron configurations that end in s2 so they have two valence electrons.

Electron Dot Diagram The column starting with Boron has electron configurations that end in s2 p1 so they have three valence electrons.

Electron Dot Diagram The column starting with Carbon has electron configurations that end in s2 p2 so they have four valence electrons.

Electron Dot Diagram The column starting with Nitrogen has electron configurations that end in s2 p3 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] 4s13d5 NOT… [Ar]4s23d4 Filled orbitals have special stability Pd: [Kr] 4d10 NOT… [Kr] 4d85s2