1. Electrons in Atoms

2. Atomic Models Atomic models are always changing
The model that was used in chapter 5 is obsolete

3. Contributions to the Model
John Dalton – Atoms were indivisible
Change – discovery of subatomic particles
J.J. Thomson – discovered electrons
Change – discovery of nucleus
Ernest Rutherford – discovered nucleus
Change – orbit of electrons
Niels Bohr – Claimed electrons orbit nucleus in various “energy levels”
Change – probability of finding electrons
Schödinger – The probability of finding an electron is represented by a cloud

4. Quantum Mechanics
Schödinger represents the probability of finding electrons on a certain energy level
This is a “s” sublevel
Where the electrons are located in relationship to the nucleus is called the Atomic Orbital

5. Atomic Orbitals S orbit S orbits can hold a maximum of 2 electrons
Alkali metals and alkaline earth metals are s-orbits

6. Atomic Orbitals P orbit P orbits can hold a maximum of six electrons
Nonmetals, Metalloids, and Noble Gases are p-orbits
Note: they also contain the s-orbit

7. Atomic Orbitals D orbit D orbits can hold a maximum of ten electrons
Transition metals are d- orbits
Note: they also contain s and p-orbits

8. Energy Levels Energy levels are represented with the letter “n”
The lowest energy level n = 1
Energy levels can hold only so many electrons
n =
n =
n =
n =

9. Electron Configurations
How electrons are configured around a nucleus
Three rules explain how to determine the configuration

10. Aufbau principle Electrons enter orbitals of lowest energy first
Increasing Energy Level

11. Pauli Exclusion Principle
An atomic orbital may describe at most two electrons
The electron pair must have opposite spins
Empty
One
Two

12. Hund’s Rule
When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with parallel spins

13. Hund’s Rule P-orbital

14. Exceptions
Not all elements follow the basic electron configuration rules
Chromium
Following rules 1s22s22p63s23p63d44s2
Correct 1s22s22p63s23p63d54s1
Copper
Following rules 1s22s22p63s23p63d94s2
Correct 1s22s22p63s23p63d104s1

15. Cont.
Half and full subshells are more stable than partially filled levels
The half filled 4s sublevels are stable