1. Chemistry 103
Lecture 7

2. Outline I. Electronic Structure (CH5) Orbitals/Quantum Numbers
Electron Configurations
EXAM I PRACTICE KEY POSTED
In glass case by office (CHE118)

3. Classical Mechanics
There is no limit to the number of observables we can measure simultaneously
These observables are continuous

4. Quantum Mechanics
Unfortunately, extremely small particles (electrons) do not follow the laws of classical (Newtonian) physics. The new physics that mathematically treats small particles is called Quantum Mechanics.

5. Electronic Structure - Quantum Mechanics
Nature of Electrons in Atoms

6. Energy Level Changes
An electron absorbs energy to “jump” to a higher energy level.
When an electron falls to a lower energy level, energy is emitted.
In the visible range, the emitted energy appears as a color.
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7. Periodicity of Periodic Table
Objective: Placing Electrons about the Nucleus
of an Atom for a Particular Element.
MODEL DEVELOPED
(Quantum Numbers)
APPLICATION
(Electron Configurations)

8. Quantum Numbers - The Model
Shell (n)
Subshell (l)
l= l= l= l=3

9. Electron Orbitals (n & l )
Region of space where two electrons are likely to be found (90% probability)
Have different shapes depending on which subshell (l quantum number) they are in

10. Orbital Shapes

11. Quantum Numbers - The Model
Shell (n)
Subshell (l)
Orientation (ml)
l= l= l= l=3
Example: l=1, ml=-1,0,1

12. How many orbitals of a given type are there?
Quantum number: ml = -l, -l +1,… 0 … +l
Covers the entire positive and negative range of “l” in increments of “1”.
Example: l = 1 (p orbital type)
ml = -1, 0 , 1
(there are 3 values, that label 3 different “p” orbitals - different orientations in space)

13. p Orbitals A p orbital Has a two-lobed shape
Is one of three p orbitals that make up each p sublevel
Increases in size as the value of n increases
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14. Electron Orbitals Orbitals
There are a different number of orbitals for each subshell (l ) type:
In an s subshell (l=0), there is 1 orbital
In a p subshell (l=1), there are 3 orbitals
In a d subshell (l=2), there are 5 orbitals
In a f subshell (l=3), there are 7 orbitals.

15. Electron Spin
The Maximum Number of Electrons any single orbital can hold is two.
They are distinguished from each other by a Quantum Number called “spin”. One electron will be given the quantum number
+1/2 ( ) and the other -1/2 ( ).

16. Learning Check Indicate the number of electrons each will hold:
A. 4s sublevel (n = 4, l = 0) (ANSWER=2)
B. 3d sublevel (n = 3, l = 2) (5 orbitals of 3d) (ANSWER = 10)
C. n = 3 (3s, 3p, 3d) (ANSWER = 18)

17. Summary of Model Electron Orbitals (n (shell) l (probability))
Number of orbitals (l ml (orientation))

18. Using the Orbital Model
ELECTRON CONFIGURATIONS &
THE PERIODIC TABLE

19. Writing Electron Configurations
Electron configurations tells us which energy levels the electrons for each element are located.
THREE GENERAL rules for placing electrons about the nucleus:

20. Writing Electron Configurations
Electron configurations tells us which energy levels the electrons for each element are located.
THREE GENERAL rules for placing electrons about the nucleus:
1. Electrons fill orbitals starting with lowest energy first.

21. Writing Electron Configurations
Electron configurations tells us which energy levels the electrons for each element are located.
THREE GENERAL rules for placing electrons about the nucleus:
1. Electrons fill orbitals starting with lowest energy first
2. There can be no more than 2 electrons in any one orbital.

22. Aufbau Diagrams 1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d ….
6s 6p ….. 7s

23. Electron Configurations
Placing electrons for an atom in orbitals by order of increasing energy
(lowest->highest) H He Li

24. Subshell Energy Order
How will you remember the energy order of the subshells? Use the periodic table!

25. Subshells and the Periodic Table

26. Practice: Electron ConfigurationsGe Rb

27. Names of Some Representative Elements
Several groups of representative elements are known by common names.
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Publishing as Benjamin Cummings

28. Abbreviated Electron Configurations
An abbreviated (noble gas shorthand) configuration shows
The symbol of the noble gas in brackets that represents completed sublevels
The remaining electrons in order of their sublevels
Example: Chlorine has a configuration of:
1s2 2s2 2p s2 3p5
[Ne]
The abbreviated configuration for chlorine is:
[Ne] 3s2 3p5

29. Practice: Electron ConfigurationsGe Rb