1. Atomic Structure Electron Configuration, Valence Electrons, and Ions

2. Quick Review Energy shells hold electrons around nucleus _ _ _ _ _ _ _
1st Shell can hold 2 electrons
2nd Shell can hold 8 electrons
3rd Shell can hold 18 electrons*
*We only ever put 8 electrons in the 3rd _ _ _ _ _ _ _ _ _
Nucleus _ _ _ _ _ _ _ _ _

3. What Atoms Want to Do
VALENCE ELECTRONS: electrons in the outermost energy shell
Atoms want their outermost shell filled with as many valence electrons it can hold:
2 valence e- in the 1st shell
8 valence e- in the 2nd shell
8 valence e- in the 3rd shell
Atoms will take, give, or share electrons to have the outermost shell filled
3 protons (3+)
How
many
valence electrons?
________
4 neutrons (0) 2
8 protons (8+)
8 neutrons (0)
How
many
valence electrons?
________ 6

4. Valence Electrons Rules
Rules to determine if an atom will gain or lose valence electrons
If atom has 8 valence electrons...
No gain or loss
Is neutral
(this includes helium with 2)
If atom has 1-3 valence electrons…
Loses them
Becomes a positive (+) ion= Cation
If atom has 5-7 valence electrons…
Gains however many it needs to have 8
Becomes a negative (-) ion = Anion
Don’t worry about atoms with exactly 4 valence electrons

5. Making Ions
Atoms will either gain or lose valence electrons to make sure the outermost shell is full
Losing or gaining valence electrons makes the atom an ion and gives it a (+) or (–) charge
ION: A positively or negatively charged atom (the atom has lost or gained an electron
2 Ways to Determine the Charge...
Protons – Electrons
11 protons – 10 electrons = 1+ charge
15 protons – 18 electrons = 3- charge
# of valence electrons lost or gained
Lost 2 valence electrons = 2+ charge
Gained 1 valence electron = 1- charge

6. Li Li 3 7 3 7 Atom vs. Positive Ion + Neutral Lithium Atom
Protons = 3
Neutrons = 4
Electrons = 3
Valence Electrons = 1
Charge = 0
3+ protons and 3- electrons
Positive Lithium Ion
Electrons = 2
Valence Electrons = 2
Charge = 1+
3+ protons and 2- electrons 3 Li
3 protons (3+)
4 neutrons (0) 7
Lithium wants to get rid of its 1 valence electron so that its outermost shell is full
Getting rid of a negative electron makes the atom positively charged. 3 Li +
3 protons (3+) 7
4 neutrons (0)

7. O O 8 16 8 16 Atom vs. Negative Ion 2- Neutral Oxygen Atom
Protons = 8
Neutrons = 8
Electrons = 8
Valence Electrons = 6
Charge = 0
8+ protons and 8- electrons
Negative Oxygen Ion
Electrons = 10
Valence Electrons = 8
Charge = 2-
8+ protons and 10- electrons 8 O
8 protons (8+)
8 neutrons (0) 16
Oxygen wants to 2 more valence electron so that its outermost shell is full.
Gaining 2 negative electrons makes the atom negatively charged. 8 O 2- 16
8 protons (8+)
8 neutrons (0)

8. An atom has a mass number (A) of 35.
Practice Problem #1
An atom has a mass number (A) of 35.
If it has 17 protons, how many neutrons does it have?
35 – 17 = 18 neutrons
What is the atomic number (Z)? 17
What element would it be?
Chlorine
If it has 17 electrons, what would the charge on the atom be?
17 protons – 17 electrons = 0 (it is a neutral atom)

9. An atom has a mass number (A) of 24.
Practice Problem #2
An atom has a mass number (A) of 24.
If it has 12 protons, how many neutrons does it have?
24 – 12 = 12 neutrons
What is the atomic number (Z)? 12
What element would it be?
Magnesium
If it has 10 electrons, what would the charge on the atom be?
12 protons – 10 electrons = 2+ (it is an ion)

10. An atom has a mass number (A) of 14.
Practice Problem #3
An atom has a mass number (A) of 14.
If it has 7 protons, how many neutrons does it have?
14 – 7 = 7 neutrons
What is the atomic number (Z) 7
What element would it be?
Nitrogen
If it has 10 electrons, what would the charge on the atom be?
7 protons – 10 electrons = 3- (it is an ion)