1. Ms. Samayoa Birmingham Community Charter High School Chemistry
Valence Electrons
Ms. Samayoa
Birmingham Community Charter High School
Chemistry

2. Learning Objective: Students will be able to identify the number of valence electrons by analyzing electron configurations Academic Vocabulary: Valence Electron

3. Dmitri Mendeleev
Mendeleev is known as the Father of the Periodic Table because he was able to predict the properties of elements before they were even discovered
However, Mendeleev did not know why certain elements have similar properties
But we do now!

4. How are properties of an element determined?
Properties of an element are determined by it’s valence electrons!

5. Valence Electron
Valence electron is an electron that is found on the OUTERMOST shell of an atom
It determines the atom’s chemical properties

6. So how do we know how many valence electrons an atom has?

7. ELECTRON CONFIGURATION!
The numbers tells you the number of SHELLS (energy levels) the atom has
S, p, d, f tells you what type of orbital the electron is in (what type of room)
The “exponent” tells you how many electrons are in those specific orbitals

8. THINK ABOUT IT…
How do we identify the number of valence electrons an atom has by its electron configuration?
Remember, that valence electrons are electrons that are found on the OUTERMOST shell of an atom
Pair-share activity

9. Electron Configuration and Valence Electrons
Write the element’s electron configuration
Identify the highest energy level in the electron configuration
Add up the electrons (“exponents”) that are found in the highest energy level
That would be the number of valence electrons an atom would have
Example:
How many valence electrons does sulfur have?
Sulfur electron configuration: 1s2 2s2 2p6 3s2 3p4
Highest energy level AKA shell: 3
Number of electrons in 3rd energy level are 2 and 4 so 2+4 = 6
Number of valence electrons is 6

10. CHECK FOR UNDERSTANDING
Find the number of valence electrons for Nitrogen. 5
Find the number of valence electrons for Phosphorous
Find the number of valence electrons for Magnesium 2

11. Remember that elements would prefer to have a FULL OUTER SHELL ELECTRONS

12. THINK ABOUT IT…
What is the difference between alkali metals and noble gases?
Alkali metals are extremely reactive and noble gases are unreactive.
What group does Potassium belong in? What group does Krypton belong in?
Potassium belong in the alkali metal group. Krypton belongs in the noble gas group.
Hence, potassium is reactive/unreactive
Hence, krypton is reactive/unreactive
Write the electron configuration for potassium and krypton.
Potassium: 1s22s22p63s23p64s1
Krypton: 1s22s22p63s23p64s23d104p6

13. Think About It (continued)…
What is the difference between potassium’s and krypton’s electron configuration?
Potassium has an unfilled outer shell electrons
Krypton has full outer shell electrons
How does this explain the main characteristics of these elements?
Because potassium does not have full outer shell electrons, it would easily react in order to have full outer shell electrons.
On the other hand, krypton already has full outer shell electrons. Thus, it would not react as easily as potassium.

16. Element
Electron Configuration
Shorthand Electron Configuration
# of valence electrons
Iodine
Xenon
Lead
Silver
Strontium
Potassium
Boron