Topic: Covalent Bonding – Lewis Dot Diagrams Do Now: Identify Bond Type from Formula AuAg CO 2 Li...
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Transcript of Topic: Covalent Bonding – Lewis Dot Diagrams Do Now: Identify Bond Type from Formula AuAg CO 2 Li...
Topic: Covalent Bonding – Lewis Dot Diagrams
Do Now: Identify Bond Type from Formula
AuAgCO2
Li3NNa2SMg
CsFH2ONaCl
SO2CuCH4
Covalent
Covalent
Covalent
Covalent
Ionic
Ionic
Ionic
IonicMetallic
Metallic Metallic
Metallic
Covalent Molecule vs Ionic Compounds
Electrons are shared
Molecules are formed
Electrons are transferred
Ions form = crystal lattice
3 representations of Molecules• Molecular Formula
– tells type and number of atoms
– H2 or O2
• Structural Formula– Shows bonds between atoms– H-H or O=O
• Lewis Dot Diagrams– Shows valence electrons shared between atoms
3 types of bonds• Single Bond – 2 shared valence electrons
– When H or Halogens (F, Cl, I, Br) bond with other atoms (or eachother) they ALWAYS form Single Bonds
3 types of bonds• Single Bond – 2 shared valence electrons
– When H or Halogens (F, Cl, I, Br) bond with other atoms or each other they ALWAYS form Single Bonds
• Double Bonds – 4 shared valence electrons
3 types of bonds• Single Bond – 2 shared valence electrons
– When H or Halogens (F, Cl, I, Br) bond with other atoms or each other they ALWAYS form Single Bonds
• Double Bonds – 4 shared valence electrons
• Triple Bonds – 6 shared valence electrons
Bonding Capacity (# of bonds formed)
00:Ne:Ne, Ar, Kr
22·O:O, S
33·N·N, P
44·C·C, Si
11·F:F, Cl, Br, I
11HH
Bonding Capacity
# Unpaired Electrons
Lewis Structure
Atom
.
..
..
.
....
..
·····
Bonding Capacity (# of bonds formed)
4 3 2 1
H2 H2O CO2
Draw these molecules on your paper…we are going to draw Lewis Dot Diagrams
Rules for drawing Lewis Diagrams1. Arrange symbols on paper the way think atoms are arranged
- Diatomics easy – next to each other- Hydrogens can never be in the middle, always on the outside- Atom with lowest electronegativity placed in center
H2 H2O
H H H O H
CO2
O C O
Rules for drawing Lewis Diagrams2. Add up # valence electrons all atoms
H2 H2O
H H H O H
CO2
O C O
2 8 16
Rules for drawing Lewis Diagrams3. Distribute electrons, start with single bonds (1 pair
of electrons) between all atoms then fill in remaining
H2 H2O
H H H O H
CO2
O C O
2 8 16
Rules for drawing Lewis Diagrams4. 2 tests
1. A) # dots = # valence electrons found in rule 2
2. B) Every atom has octet (8) (except H – only wants 2)
H2 H2O
H H H O H
CO2
O C O
2 8 16Bonding electrons get counted 2 times –once for each atom sharing them
Assessing Lewis Diagrams
• If dot structure passes both tests, you’re finished
• If fails one or both tests, try again
• If single bonds don’t work - try multiple bonds – ALWAYS MOVE PAIR OF ELECTRONS between atoms
CO2
O C O
16
CO2
O C O
16CHECK AGAIN1. A) # dots = # valence
electrons found in rule 2
2. B) Every atom has octet (except H – only wants 2)
O=C=O
Try some examples
• H2, F2, HF, O2, N2
• Step 1: Draw symbols the way think atoms are arranged
–Diatomics easy – atoms next to each other!
Drawing Lewis Diagrams
H H
Step 2: Count up the valence electrons
Each H has 1 valence electron so the total = 2
Step 3: Distribute the valence electrons, starting with single bonds between all atoms
:
Testing Lewis Diagrams
H H:Test 1: 2 dots in diagram = 2 valence electrons
Test 2:Each H has 2 valence electrons (Remember H only wants 2)
Testing Lewis Diagrams
F FStep 1
Step 2 2 X 7 = 14 valence electrons
Step 3 F F: : :..
..
..
..
Try HF
H FStep 1
Step 2 7 + 1 = 8 valence electrons
Step 3 H F: :..
..
O OStep 1:
Step 2: 2 X 6 = 12 valence electrons
Step 3: O O:: :..
..
..
Step 4: Test failed
No Good!
Try O2
Try O2 Again!
O OStep 1:
Step 2: 2 X 6 =12
Step 3: Distribute electrons (single bond between atoms didn't work so try a double bond)
::..
..
..
..
Step 4: Test!
Try N2
N NStep 1:
Step 2: 2 X 5 = 10 electrons
Step 3: Distribute electrons starting with a single bond between the nitrogen atoms
: ..
: .. :
Step 4: Test
No Good!
Try N2 with a double bond
N N::: :..
No Good!
Try N2 with a triple bond
N N:::: :
Step 4: Test