1. Let’s review Oxygen O 8 1s2 2s2 2p4 Oxygen has 6 valence electrons.
Symbol?
Atomic Number?
Protons?
Electrons?
Electron Distribution?
Oxygen has 6 valence electrons.
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2. Electron Dot Diagrams
Atom’s symbol surrounded by dots to represent its valence electrons
Example
Oxygen
6 valence electrons
Lithium
1 valence electron
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3. Problem Set 1
Draw the Electron Dot Diagrams for: Magnesium Helium Krypton Aluminum Bromine Potassium Nitrogen Silicon Strontium
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4. Lewis Structure
Diagram representing the arrangement of valence electrons in a molecule
Most atoms need 8 valence electrons to become stable. The exceptions are H and He which need 2 valence electrons to be stable.
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5. H - H Lewis Structure for H2 2 electrons belonging to both atoms
Represented by a dash between the symbols
H - H
Shared pair
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6. Lewis Structure for Cl2 Shared pair Unshared pair
Each Cl atom has 7 valence electrons; giving a total of 14 valence electrons to work with.
Shared pair
Unshared pair
Electrons belonging to only one atom
Represented by 2 dots
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7. Lewis Structure for HCl
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8. When more than two atoms bond, you must determine which is central.
The central atom is:
Frequently carbon
Never hydrogen
Often atom with the smallest electronegativity H
Lewis structure for CH3I
(There are a total of 14 valence electrons to work with.) H C I H
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9. (Hint: The carbon atoms form a ring.)
Problem Set 2
NH3
CH2Cl2
CH3OH
(a little tricky)
C6H12
(Hint: The carbon atoms form a ring.)
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10. Lewis structure of ethene, C2H4
(has total of 12 valence electrons) H H C C H H
Type of bond
Pairs of electrons shared
Single bond 1
Double bond 2
Triple bond 3
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11. Problem Set 3
CO2 HCN CH2O C2HCl
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12. [ ]-1 O N O O Polyatomic Ion
Covalently bonded groups of ions with a charge
NO3-1
Has gained 1 electron to give a total of 24 valence electrons to work with
N = 5 electrons
O = 3 x 6electrons = 18 electrons
-1 = 1 extra electron
[ ]-1 O N O O
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13. Problem Set 4
PO4-3 SO4-2 NH4+1 CN-1
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