Transcript Electron Configurations Chapter 5 Section 3 Vocabulary electron configuration aufbau principle Pauli exclusion principle Hund’s rule Valence electron Electron-dot structure Review Each principal energy level can have the same number of sublevels.

Electron Configurations
Chapter 5
Section 3
Vocabulary
electron configuration
aufbau principle
Pauli exclusion principle
Hund’s rule
Valence electron
Electron-dot structure
Review
Each principal energy level can have the
same number of sublevels as the level
number
Each sublevel orbital has a different shape
Each orbital can have only 2 electrons
What does this mean?
Electron Arraignment follows
Rules
Low energy level systems are more stable than
high-energy systems


Atoms will assume the electron arrangement that
gives the atom the lowest energy
Most stable is the “ground state” (lowest energy)
Three rules/principles for arranging electrons



Aufbau
Pauli Exclusion principle
Hund’s Rule
Aufbau Principle
Each electron occupies the lowest energy
level available

Learn the sequence of atomic orbitals from
lowest to highest:
Aufbau Diagram
#4 – also do electron DOT diagram, #7 & 8 – SHOW YOUR WORK
Aufbau Expanded
Using Aufbau
All orbitals related to the same energy level are
of equal energy

All 2p orbitals have the same energy
In a multi-electron atom, the energy sublevels
within a principal energy level have different
energies:

2p orbitals are higher energy than 2s orbitals
The sequence of sublevels within a principle
level in increasing energy is: s, p, d, and f
Orbitals related to energy sublevels within one
principle energy level can overlap orbitals
related to another principal level

Notice: 4s is lower than 3d
Pauli Exclusion Principle
Each electron has an associated spin, like
a top

Can spin on bottom
or top
Each orbital can hold AT MOST 2
electrons, but only if they have opposite
spin

Designated as:
Hund’s Rule
Because negatively charged electrons
repel each other, they try to get as far
away from each other as possible,
therefore:
Single electrons with the same spin will
occupy each equal energy orbital before
additional electrons with opposite spins
occupy the same orbitals.
WHAT?
Hund’s Rule
3
241
Representing Atom’s Electrons
1. Orbital Diagrams
2. Electron Configuration Notations
Orbital Diagrams
Draw one box for each orbital




Empty box means no electrons
Box with single up arrow means orbital with
one electron
Box with two arrows (up/down) means orbital
with two electrons
Each box is labeled with the principle
quantum number and the sublevel
Example:
Example Orbital Diagram - N
Example Orbital Diagram – C & O
Electron Configuration Notation
Specify principal energy level and energy
sublevel
Use a superscript to represent the number
of electrons

Use the Aufbau diagram to help you
remember the level/sublevel filling order
Examples:
Electron Configuration Notation
Electron Configuration Notation
Element
ECN
Element
ECN
Hydrogen
1s1
Carbon
1s2 2s2 2p2
Helium
1s2
Nitrogen
1s2 2s2 2p3
Lithium
1s2 2s1
Oxygen
1s2 2s2 2p4
Beryllium
1s2 2s2
Fluorine
1s2 2s2 2p5
Boron
1s2 2s2 2p1
neon
1s2 2s2 2p6
A Variation – Noble Gas
Notation
Similar to Electron Configuration Notation,
but:


Start with the previous noble gas, and put that
symbol in brackets
Add electrons to the noble gas
Example:
Sodium (Na) = [Ne] 3s1


Ne = 1s2 2s2 2p6
Na = 1s2 2s2 2p6 3s1
Exceptions to Aufbau
Cr (Chromium) = [Ar] 4s1 3d5
Cu (Copper) = [Ar] 4s1 3d10
Valence Electrons
Only Valence Electrons contribute to
chemical bonding
Valence Electrons = electrons in outer
most principal energy level

Generally highest energy
Examples:


Carbon: [He] 2s2 2p2 has 4 valence electrons
Sulfur: [Ne] 3s2 3p4 has 6 valence electrons
Electron Dot Diagrams
Also called Lewis Electron Dot Diagrams
or Lewis Electron Dot Structure or Electron
Dot Structure
Shows atomic symbol and ONLY valence
electrons
Electron Dot Diagrams
Periodic Table