Download Double Bonds – 4 shared valence electrons

Topic: Covalent Bonding – Lewis Dot
Diagrams
Do Now: Identify Bond Type from Formula
CH4 Covalent Cu
NaCl
Mg
CO2
Ionic
Metallic
SO2 Covalent
H2O Covalent CsF
Ionic
Metallic Na S
Ionic Li3N
Ionic
2
Covalent Ag Metallic Au 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)
Atom
H
F, Cl, Br, I
O, S
N, P
C, Si
Ne, Ar, Kr
Lewis
Structure
.
H
..
·F:
..
..
·O:
.
..
·N·
..
·C·
·
··
:Ne:
··
# Unpaired
Electrons
Bonding
Capacity
1
1
1
1
2
2
3
3
4
0
4
0
Bonding Capacity (# of bonds
formed)
4
3
2
1
Draw these molecules on your paper…we are
going to draw Lewis Dot Diagrams
H
2
H2O
CO
2
Rules for drawing Lewis Diagrams
1. 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
H
2
H H
H2O
H O H
CO
2
O C O
Rules for drawing Lewis Diagrams
2. Add up # valence electrons all atoms
H
CO
H H
H2O
H O H
O C O
2
8
16
2
2
Rules for drawing Lewis Diagrams
3. Distribute electrons, start with single bonds (1 pair
of electrons) between all atoms then fill in
remaining
H
H2O
H H H O H
2
2
8
CO
2
O C O
16
Rules for drawing Lewis Diagrams
4. 2 tests
1. A) # dots = # valence electrons found in rule 2
2. B) Every atom has octet (8) (except H – only wants 2)
H
H2O
H H H O H
2
2
8
CO
2
O C O
16
Bonding 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
CO
2
CO
2
O C O
O C O
16
16
CHECK AGAIN
1. 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
Test 1:
2 dots in
diagram =
2 valence
electrons
H :H
Test 2:
Each H has 2
valence electrons
(Remember H
only wants 2)
Testing Lewis Diagrams
Step 1
Step 2
Step 3
F F
2 X 7 = 14 valence electrons
.. ..
: ..F : F.. :
Try HF
Step 2
Step 3
HF
7 + 1 = 8 valence electrons
..
:
H F
..
:
Step 1
Try O2
Step 1:
OO
Step 2:
2 X 6 = 12 valence electrons
Step 3:
.. ..
: O :O :
..
Step 4: Test failed
No Good!
Try O2 Again!
Step 1:
Step 2:
2 X 6 =12
.. ..
::O
O
.. ..
Step 3: Distribute electrons (single bond between
atoms didn't work so try a double bond)
Step 4: Test!
Try N2
Step 1:
Step 2:
..
:N
:
:
N
..
No Good!
2 X 5 = 10 electrons
Step 3: Distribute electrons starting with a single
bond between the nitrogen atoms
Step 4: Test
Try N2 with a double bond
: N :: N :
..
No Good!
Try N2 with a triple bond
: N ::: N :
Step 4: Test