1. Electron Configurations
…and now, the rest of the story

2. Recall
An electron configuration (EC) shows the location of all electrons in an atom or ion.
In an atom, number of electrons = number of protons = atomic number
Electrons are found around the nucleus of an atom in specific energy levels.

3. 1st energy level
--has one sublevel, the 1s (for spherical) sublevel.
--Any s sublevel has one orbital,
--Any orbital can hold two electrons
So the electron configurations of hydrogen and helium are written
1H 1s1
2He 1s2

4. 1H 1s1
2He 1s2
The 1 refers to the energy level

5. 1H 1s1
2He 1s2
The s refers to the sublevel

6. 1H 1s1
2He 1s2
The superscripts are the number of electrons in this sublevel.

7. 2nd energy level --has two sublevels, the 2s and 2p sublevels.
The 2s sublevel
-is spherical,
-has one orbital, and
-can hold two electrons (just like the 1s),
but it is larger than the 1s sublevel.

8. The 2s sublevel…
-- is in a higher energy level,
--the electrons in it have more energy than 1s electrons, and
--average a greater distance from the nucleus.

9. The 2p sublevel has three p orbitals
--they have two lobes each,
--lie in three perpendicular axes (x, y, and z),
--can hold two electrons each,
…so the 2p sublevel (and any p sublevel) can hold six electrons

10. 2nd energy level
-has 2s (bigger, still spherical) and 2p (has 3 bi-lobed orbitals in x, y, and z directions)
-holds up to (2 in s + 3 x 2 in p)=8 electrons total

11. 3Li 1s22s1
4Be 1s22s2
5B 1s22s22p1
6C 1s22s22p2
7N 1s22s22p3 …

12. The 3rd energy level
has three sublevels, 3s, 3p, and 3d. The s and p sublevels are similar in structure (but bigger) than the s and p sublevels seen before.

13. The 3d sublevel Any d sublevel has five orbitals of varying shapes.
These orbitals can hold two electrons each for a total of ten electrons.
The 3d sublevel is the highest energy sublevel of energy level 3,
Energy level 4 begins to fill (the 4s sublevel fills) before the 3d sublevel

14. D sublevels

15. The 4th energy level
has four sublevels (notice the trend?) They are 4s, 4p, 4d, and 4f.
The s, p, and d sublevels are structured as before.

16. The f sublevel has seven orbitals, and can hold up to fourteen electrons.
The 5s sublevel is filled before the 4d, and the 5p and 6s sublevels precede the 4f.
Let’s look at a picture instead

17. Out of Order! 1) 1s 2) 2s 2p 3) 3s 3p 3d 4) 4s 4p 4d 4f
5) 5s 5p 5d 5f (…g?)
6) 6s 6p 6d …
7) 7s 7p

18. Please review S 1 orbital 2 electrons P 3 orbitals 6 electrons
D 5 orbitals 10 electrons
F 7 orbitals 14 electrons

19. The Aufbau diagram
Boxes are orbitals, each can hold two electrons

20. The Aufbau order of sublevels
All Electron configurations are some subset of the order shown below. Only the last sublevel might be incomplete
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6…

21. Three rules for filling orbitals
Aufbau (building up) principle—lower energy sublevels are filled first
Pauli exclusion principle—electrons sharing an orbital must have opposite spins
Hund’s Rule—when a sublevel has several orbitals, electrons will distribute to separate orbitals with parallel spins, before sharing orbitals with opposite spins

22. Watch out for two things
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6…gets really old eventually. Look for the last octet and describe it as a noble gas core electron configuration
Ex: 87Fr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s can be written
87Fr [Rn] 7s1 (because radon is a noble gas, and accounts for the first 86 electrons)

23. Practice
Write the full EC for Titanium (element 22) and write the EC with a noble gas core

24. Practice
Write the full EC for Titanium (element 22) and write the EC with a noble gas core
A) Ti 1s2 2s2 2p6 3s2 3p6 4s2 3d2
and Ti [Ar] 4s2 3d2

25. Watch out for two things
Chromium, copper and a few others rearrange electrons to get a more stable arrangement. The sublevel energies go down when a sublevel is full or half full.
Cr 1s2 2s2 2p6 3s2 3p6 4s2 3d4 becomes
Cr 1s2 2s2 2p6 3s2 3p6 4s1 3d and
Cu 1s2 2s2 2p6 3s2 3p6 4s2 3d9 becomes
Cu 1s2 2s2 2p6 3s2 3p6 4s1 3d10

26. Problems:
1. Write the electron configurations for phosphorus and nickel. Then draw the aufbau diagrams for these elements.
2. Write the complete electron configurations for magnesium, sulfur, and potassium. Then write their electron configurations using the symbols for the noble gases.
3. What element is represented by [Ne]3s23p6?
4. Determine the electron configuration for the last SUBLEVEL of the following elements: S, Pt, Sr, K, and Al.

27. 5. The an unknown element has an electron configuration of 1s22s22p63s23p4.
A. What is the element?
B. What does the superscript 6 refer to?
C. What does the letter s refer to?
D. What does the coefficient 3 refer to?
6. Write the electron configuration for calcium, a nutrient essential to healthy bone growth and development.
7. Write the electron configuration for copper, which is used in pennies.

28. 8. Use the symbols for the noble gases to write the electron configurations for the following elements:
A. Zr B. U C. Rn
9. Write the electron configuration and draw the orbital diagrams for the following elements:
A. Carbon B. Silver C. Aluminum

29. VOCABULARY Electron configuration Atomic number Energy level
Valence level
Sublevel
s,p,d,f
Orbital
Spin
Proton
Electron
Spherical
Two-lobed
Dumbell-shaped
Aufbau principle
Pauli’s exclusion principle
Hund’s rule

30. Be able to: Describe the levels, sublevels, and orbitals.
Recreate the aufbau order from the periodic chart
Write a complete EC and EC with a noble gas core for any element
Determine the last sublevel, and number of electrons there from a position on a periodic chart
Identify a position on the chart and the element from an EC
Fill out an aufbau diagram for any element