Chapter 5 Sec. 3 Electron Configurations NOTES

Electron Configuration
o Electron Configuration:
o The most stable electron configuration is the ground-state electron configuration.
o 3 Rules for Electron Configuration YOU MUST KNOW!!!
 (1) Aufbau Principle
 (2) Pauli Exclusion Principle
 (3) Hund’s Rule
o (1) The Aufbau Principle
 Definition:
An Aufbau Diagram is also
known as an Orbital
Diagram and is used for
Orbital Notation
o (2) The Pauli Exclusion Principle
 Definition:

Electrons in orbitals can be represented by arrows in boxes or over a line (the following
electrons are written in ORBITAL NOTATION or drawn in an ORBITAL DIAGRAM):

The maximum number of electrons related to each principal energy level equals 2n 2
 Ex) Principal Energy Level 3 can have a maximum of how many electrons?
 s sublevels hold max ___________________________
 p sublevels hold max ___________________________
 d sublevels hold max ___________________________
 f sublevels hold max ___________________________
o (3) Hund’s Rule
 Definition:



All orbitals must be half filled before they starting filling all the way up
Hund’s Rule Example:
Electron Arrangement
o An atom’s electron configuration can be written in two different forms:
 (1)
 (2)
o Orbital Diagrams/Orbital Notation
 Electrons in orbitals can be represented as arrows in either boxes or above a line
 Example:
o Electron Configuration Notation
 Designates the principal energy level and energy sublevel associated with each of the
atom’s orbitals and includes a superscript representing the number of electrons in the
sublevel
 Follows a pattern on the Periodic Table – read the Periodic Table like a book!
 Example:

Noble-gas Notation
 Short-hand method of representing electron configurations using a noble gas
 Noble gases are at the end of the Periodic Table in the last column
 Example:
o Review Example: Provide the electron configuration, the noble-gas electron configuration, and
the orbital diagram/orbital notation for Carbon (C).

Electron Dot Structures
o Deal with valence electrons
o Valence Electrons
 Characteristics:

Example: S (sulfur)
o You can find the number of valence electrons by looking at the group number for the element.
The general trend is that the number of valence electrons is the last digit of the group number.
 Look at the Periodic Table and identify how many valence electrons are in the following
elements:
 Lithium (Li) =
 Carbon (C) =
 Sulfur (S) =
 Neon (Ne) =
o Drawing Electron-dot Structures
 Consist of the element’s symbol and the number of valence electrons for that element.
 Example #1: Nitrogen (N)

Example #2: Neon (Ne)

FINAL EXAMPLE
o Provide (1) the electron configuration, (2) the noble-gas notation, (3) the orbital diagram
(notation), and (4) the electron-dot structure for Bromine (Br).