1. Electrons in Atoms Electron Configuration
Chapter 4
Electrons in Atoms
Electron Configuration

2. Electron Configuration
the arrangement of electrons in the atom
There are three rules we need to follow when building an atom.

3. 1. Aufbau Principle German for Building Up
When we build an atom with its various electrons we start with the lowest energy level and build up.
Lowest energy level is closest to the nucleus

4. Filling Order 7s 7p 7d 7f 7g 7h 7i 6s 6p 6d 6f 6g 6h 5s 5p 5d 5f 5g
further away from the nucleus the higher the energy
All sublevels beyond the f sublevel is theoretical
Lowest Energy
Nucleus

5. The easy way to remember the filling order
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2
2 electrons

6. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2
4 electrons

7. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2
12 electrons

8. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2 3p6 4s2
20 electrons

9. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2
38 electrons

10. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2
56 electrons

11. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2
88 electrons

12. Fill from the bottom up following the arrows
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6
118 electrons No elements with more

13. Increasing energy 7s 2p 3p 4p 5p 6p 7p 3d 4d 5d 6d 6s 5s 4f 5f 4s 3s

14. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p

15. 2. Pauli Exclusion Principal
No two electrons can have the exact same four quantum numbers!
Each orbital has no more than 2 electrons– they must have opposite spins

16. 3. Hund’s Rule
When electrons occupy orbitals of equal energy they don’t pair up until each orbital has one electron.

17. Three ways to write electron configuration
Orbital Notation
Electron Configuration Notation
Noble Gas Notation

18. Orbital Notation
Represents each orbital in the sublevel as a box or a line
Each electron is represented by an arrow pointing up (+1/2 spin) or down (-1/2 spin)
Ex: phosphorous with 15 electrons

19. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p
The first two electrons go into the 1s orbital
Notice the opposite spins
only 13 more
Lets find the electron configuration for phosphorous with 15 electrons

20. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p
The next electrons go into the 2s orbital
only 11 more

21. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p
The next electrons go into the 2p orbital
only 5 more

22. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p
The next electrons go into the 3s orbital
only 3 more

23. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s
The last three electrons go into the 3p orbitals.
They each go into separate orbitals
3 unpaired electrons

24. Electron Configuration Notation
Represents each sublevel designation from lowest energy to highest
Electrons are represented by superscripts
Sublevel Maximum
# of e- s
p 6
d 10
f 14

25. Electron Configuration Notation
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6

26. Electron Configuration Notation
Ex: Manganese 25 electrons
From lowest energy to highest
Follow the filling order
1s22s22p63s23p64s23d5

27. Try these Na F Cl Ca

28. Answers Na 1s2 2s2 2p6 3s1 F 1s2 2s2 2p5 Cl 1s2 2s2 2p6 3s2 3p5
Ca 1s2 2s2 2p6 3s2 3p6 4s2

29. 3. Noble Gas Configuration
Place the noble gas that precedes the element in brackets [ ]
this accounts for that number of electrons
Continue the electron configuration with the next highest principal energy level (period number) and the s orbital
This is a shorthand way of writing electron configuration.

30. Noble Gas Configuration
Ex: Silicon 14 electrons
1s22s22p63s23p2
same as the noble gas Ne
Si is in period 3
[Ne] 3s23p2

31. Exceptions to Electron Configuration
There’s always exceptions

32. Orbitals fill in order Lowest energy to higher energy.
Adding electrons can change the energy of the orbital.
Filled and half-filled orbitals have a lower energy.
Makes them more stable.
Changes the filling order of d orbitals

33. Write these electron configurations
Titanium - 22 electrons
1s22s22p63s23p64s23d2
Vanadium - 23 electrons
1s22s22p63s23p64s23d3
Chromium - 24 electrons
1s22s22p63s23p64s23d4 is expected
But this is wrong!!

34. Chromium is actually 1s22s22p63s23p64s13d5 Why?
This gives us two half filled orbitals.

35. Chromium is actually 1s22s22p63s23p63d54s1 Why?
This gives us two half filled orbitals.

36. Chromium is actually 1s22s22p63s23p63d54s1 Why?
This gives us two half filled orbitals.
Slightly lower in energy.
The same principle applies to copper.

37. Copper’s electron configuration
Copper has 29 electrons so we expect
1s22s22p63s23p64s23d9
But the actual configuration is
1s22s22p63s23p64s13d10

38. Copper’s electron configuration
This gives one filled orbital and one half filled orbital.
Remember these exceptions
s2d4  s1d5
s2d9  s1d10

39. In each energy level
The number of electrons that can fit in each energy level is calculated with maximum e- = 2n2 where n is energy level
n = 1 maximum e- = 2
n = 2 maximum e- = 6
n = 3 maximum e- = 18 …