1. 5.3 ELECTRON CONFIGURATIONS

2. 5.3 ELECTRON CONFIGURATION Arrangement of electrons in the atom:
Electron Hotel:
1) Stays in the cheapest
(lowest energy) room possible.
2) No more than 2 (electrons) to a room.
3) Likes having own room. Will share if next room is more expensive.
4) “d” & “f” suites are
especially expensive!

3. AUFBAU PRINCIPLE – Each electron will occupy the lowest energy orbital available
Chart shows lowest to highest energy.
Note all p, d, & f electrons in same energy level have same energy.
“Energy overlap” of “d” & “f” electrons.
Aufbau Hotel

4. PAULI EXCLUSION PRINCIPLE Each electron is unique:
Unique by energy level, shape, orientation in space or spin
If 2 electrons are in the same orbital, they must have opposite spins: 
Aufbau Hotel electrons:
1 goes to football game ↑
1 goes to the opera ↓

5. HUND’S RULE – Use when filling p, d, f orbitals:
Must fill in single electron, same spin in each orbital before pairing up.
Ex.    then   _
p p
Hotel: Electrons like having own room,
unless next available room is more
expensive. Then they will share.

6. QUIZ
1) According to Aufbau, electrons fill the orbital having the ___ energy.
2) Pauli’s Exclusion Principle states that each electron is _____. If 2 electrons are in the same orbital they must have ____ spins.
3) Hund’s Rule states that when filling p, __, and f orbitals, you must first fill in single electron, same ___ in each orbital before pairing up.

7. Predicting last part of electron configuration Use periodic table:
Period– tells what energy level being filled.
(Ex. Na – 3rd energy level)
Sublevels Groups
s a – 2a (& He)
p 3a – 8a
d “B groups”
f Lanthanide & Actinides
(bottom 2 rows)

8. LOCATION OF s, p, d, f BLOCKS
d block – 1 step behind
f block steps behind

9. What is the ending for the following elements:
3) Li
4) Na
5) Mg
6) Al
7) Ar
8) K
9) Sc (“d” is 1 step behind)
10) U (“f” is 2 steps behind) 5f4

10. WRITING ORBITAL DIAGRAMS: Ex. O
1) Find atomic #. Gives #electrons (arrows).
For O, atomic # = 8
2) Find what O ends in.
2 p4.
3) Draw orbitals (slots) from lowest (1s) to 2p4.
__ __ __ __ __ Now draw in arrows.
1s 2s p
Use Hotel rules:

11. FILL IN FROM LOWEST TO HIGHEST:

12. ELECTRON NOTATION
Summarize arrows
Called notation:
1s2 2s2 2p4

13. Write electron configuration (arrows) for Nitrogen.
1) N = #7 (7 electrons or arrows).
2) N ends in 2p3.
3) Draw orbitals up to 2p: (show all slots)
__ __ __ __ __ Now draw in arrows.
1s 2s 2p
Notation is 1s22s22p3

14. LEVEL 1 ASSIGNMENT: Write electron configuration (arrows) for: 1) F 2) Mg 3) O 4) P
1) Find atomic #.
2) Element ends in ____.
3) Draw orbitals up to ___: (show all slots)
__ __ __ __ __ Now draw in arrows.
1s 2s 2p
__ ___ ___ ___
3s p
4) Show notation:

15. NOBLE GAS NOTATION: Short Cut:
1) Write previous noble gas in brackets.
2) Then write each block that is left over.
Ex. for P, # 15. What is the previous
noble gas?
1) Write previous noble gas: Ne
This represents Neon’s 10 electrons.
2) Write what is left over (each block):
Ne 3s23p3.

16. SHORTHAND NOTATION Find for:

17. WRITE IN SHORTHAND (NOBLE GAS) NOTATION FORM::
1) Ca #20 (previous noble gas?)
Ar Now, what’s left over?
Ar 4s2.
2) S #16
Ne 3s23p4
3) Zr, #40
Kr 5s24d2

18. LEVEL 2 ASSIGNMENT: Write electron configuration (arrows) for: 1) K 2) V 3) Ge 4) Tc
1) Find atomic #.
2) Element ends in ____.
3) Draw orbitals up to ___: (show all slots)
__ __ __ __ __ Now draw in arrows.
1s 2s 2p
__ ___ ___ ___
3s p
4) Show notation: 1s2….
5) Show Shorthand notation: Noble gas Left over.

19. VALENCE ELECTRONS – Electrons in the atom’s outermost energy level
Determine the chemical properties of the element.
Include: s & p orbitals only
d & f are in lower energy levels (not valence)
Cl – 1s2 2s2 2p6 3s23p5
Outermost energy shell: n = 3
Valence electrons: s23p5
7 val. e-

20. PROBLEM: Find valence electrons for:
Sodium (#11)
1 valence electron (n=3)
Nitrogen (#7)
5 valence electrons
(n=2)
Argon (#18)
1s2 2s2 2p6 3s23p6
8 val. electrons
(8 is stable!)
n=3

21. FIND VALENCE ELECTRONS FOR: Valence electrons determine chemical properties!
2) Sr
3) Ra
What do you notice?
4) N
5) As
6) Kr
7) V
8) La

22. NOTE: Valence electrons do not include “d” or “f” electrons!

23. NOBLE GASES – Have filled outer shells
8 valence electrons - stable octet!
(He – has 2)
Ar (#18)
1s22s22p6 3s23p6 (8 val.)
He (#2 ) 1s (1st shell – full)
Noble Gases end in “p6”

24. NOBLE GASES HAVE FILLED OUTER SHELLS!
All end in: p6 8 val. electrons
Except: He (#2 ) 1s val. Electrons
(1st shell is full!)

25. EXCEPTIONS Half filled and filled sets of s & d orbitals very stable:
Expected: Cr Ar 4s23d4
Actual: Ar 4s13d5
Ar ↑_ ↑_ ↑_ ↑_ ↑_ _↑_
4s 3d
Complex chemistry of transition
elements.

26. EXCEPTIONS (cont.) Actual configuration: Cu #29
Predicted configuration:
[Ar] 4s2 3d9
Actual configuration:
[Ar] 4s1 3d10
Note: full “d” is stable.

27. CARBON FORMS 4 BONDS BECAUSE OF sp3 HYBRIDIZATION:
Expected orbital configuration
sp3 hybridization causes 4 like orbitals
Carbon forms 4 bonds

28. BORON ALSO HYBRIDIZES:
B forms 3 bonds!

29. THE END