Understanding the Lewis Octet Rule in Chemical Bonding

1.
What’s `shared’ in a shared electron bond  ?
Answer:
Just the outer shell or `valence’ electrons of
bonding atoms.
:
S
:
..
The main
`visual ’:
Lewis dots
Exercise 2.1 
1          2                                                                                      3        4      5       6
Inert gas core electrons for S
‘Valence’ vs `Core’ electrons
Valence
 shell or outer shell of S
How many
total electrons
does 
S 
have 
?
16
How many
 valence
electrons does 
S
have ?
6
How many `core’
electrons does 
S
 have ?
10
(Ne)
 
:
S
:
.
Dot picture shows only 
valence
electrons
 
..
Practice a few….exercise 2.2
2.
 
What rules govern the number of bonds to the
elements and how do we use these rules to build
organic (and other non-ionic) compounds ?
 
 
“If you can count to 8,
even you can do it,
maggot…..”
 
Uncle `Gil’
sez:
Gilbert
 
Newton 
Lewis:  (Uncle Gil)
Am
er
i
can
 Ch
em
ist
 
Na  +     Cl
 
e-
 
Na
+
       Cl
-
 
(+) and (-)attracted to each other
to form ionic bond
 
+
 
11 e
-
 
 
10 e
-
 
17 e-
 18 e-
Ne
Ar
Foundations of the `Lewis Octet’ Rule
What we learned From chapter 2:
 
# valence
electrons ?
 
8
 
8
 
like 
Ne
 
Like 
Ar
 
   
..
: [
X
]:
 
..
all atoms (
X
)  want to
look like this,whether
ionic or not ionic
 
DOT PICTURE VISUAL
 
Lewis `octet’ is the
most stable form
of elements
How to build a covalent compound using `Lewis Rules’
(same process as on pp 102-106 of text.
The Lewis Octet Rule
 
1) Count all the 
valence
 electrons on all the
bonding elements
 
Ex. CO
2
Valence e- on C        = 1 x 4  = 4
Valence e- on 2O     
=
 2 x 6  = 12
 total valence e-       =  4+12= 16
USING THE `OCTET’ RULE
How to build a covalent compound using `Lewis Rules’
(same process as on pp 102-106 of text)…the Lewis Octet Rule
(continued)
2)
Start by drawing single bonds to each
atom and compute the total number of
electrons in those
.
 
Ex.  O-C-O
Electrons in bonds= 2 bonds x 2
e-/bonds                                  = 4
How to build a covalent compound using `Lewis Rules’
(same process as on pp 102-106 of text) ….
continued
 
3
) Distribute the remaining valence electrons
not
 in bonds one by one and evenly to each
element in the  molecule. If an element
reaches an `octet’,  stop  placing electrons on
it and distribute what’s left to  the other
elements.
 
Ex
.  O-C-O
Electrons not in bonds = 16-4=12
Distribute them evenly
among C and O
How to build a covalent compound using `Lewis Rules’
(same process as on pp 102-106 of text) ….
continued
Ex.  O-C-O
 
4) 
Check each atom for an octet. If all have octets, you
have the right Lewis structure. If not, go back to step 2,
include a double bond somewhere and repeat steps 2-4
until a complete octet is achieved around each element
assuming the given electron count
 
x
 
 
x
 
 
 O=C-O
Electrons in bonds
= 3 bonds x 2 e-/bonds
= 6
Electrons not in bonds =  16-6 =10
 
Step 3 
repeat: distribute 10 non-bonded
electrons evenly
Step 2 
repeat: add another bond
 
Skip C now…has octet
 
Step 4 
repeat
: check to see if every element has
an octet
 
x
 
 
 O=C-O
Electrons in bonds
= 3 bonds x 2 e-/bonds
 = 6
Electrons not in bonds =  16-6 =10
 
Step 3 
repeat: distribute 10 non-bonded
electrons evenly (into lone pairs)
Back to Step 2 
repeat: add another bond
 
Skip C now…has octet
 
Step 4 
repeat
: check to see if every
element has an octet
 
x
 
 
 O=C=O
Step 2 
repeat repeat: add yet another bond
Electrons in bonds
   =  4 bonds x 2 e-/bonds
   =  8
Electrons not in bonds =  16-8 =8
 
Step 3 
repeat repeat: distribute 8 non-bonded
electrons evenly (into lone pairs)
 
Step 4 
repeat repeat
: check to see if every
element has an octet
 
Skip C..already has octet
 
 O=C=O
LEWIS PREDICTION FOR BONDING IN CO
2
Some helpful Lewis language:
bond pairs  vs 
lone pairs
 
 Bond pairs (2 e-/bond):  one line = 1 bond
 
Lone pair (2 e- per pair): 2 dots = one pair
2.
 
2) What rules govern the number of
bonds to the elements and how do we use
these rules to build organic (and other
non-ionic) compounds ?
 
LEWIS
(OCTET)
RULE
Lewis’ s Answer:
EXERCISE 2…. PLAYING
THE LEWIS ELECTRON
DOT GAME
Mole $$ !!!!
Doc’s annoying question habit
rears it ugly head again….
???
???
How do we know what `hooks’ to what
in more complicated molecules ?
 
Examples where confusion can arise:
 
CO
2
 
C-O-O or O-C-O   ??
 
SO
2
 
S-O-O  or O-S-O   ??
 
        C
O            O
 
       S
O            O
 
What
about
rings ?
“I am so
annoying…”
 
Simple rule of thumb #1:
Elements closer to the center of
the Periodic Table tend to be in
the center of a molecule
CO
2
C-O-O or O-C-O   ??
SO
2
S-O-O  or O-S-O   ??
Applying Rule of Thumb 1 to CO
2
 
`
center’ line
 
`center’
of Table
 
C
 is closer to center
line=> 
C
 in center of 
C
O
2
 
C-O-O or O-C-O   ??
Applying Rule of Thumb 1 to SO
2
 
S
 is closer to 
center
=>
S
 in center of 
S
O
2
 
S-O-O  or O-
S
-O   ??
        C
O            O
       S
O            O
What
about
rings ?
 
Simple rule of thumb #2:
Compound structures tend to
minimize `strain’  and maximize
bond angles
Doc’s questions  revisited
1.
What’s `shared’ in a shared electron bond  ?
 
2.
What rules govern the number of bonds to the
elements and how do we use these rules to build
organic (and other non-ionic) compounds ?
 
3.
How do we `read’ organic compound formulas
and deduce their bond and electron
arrangements 
?
???
Valence electrons only; 2 per bond
Lewis Octet Rule + Rules of Thumb 1 and 2
The simple as 1,2,3,4 …HONC bonding rules
(for organic compounds only)
 
Element
   
bond count to element
   
lone pairs on element
H
  
1
    
0
O
  
2
    
2
N
  
3
    
1
C
  
4
    
0
*USE FOR EXERCISE 2.4
O, N & C BOND COUNT + 
LONE PAIR 
COUNT = 4
Simple Bonding Rules for Organic* compounds:
 
the HONC Rules
 
EXAMPLE #1: ethane   (C
2
H
6
)
= one of the `
natural’ gases
 
*
Compounds made of C+ H with options to include O and N
 
EXAMPLE #2: ethanol  (C
2
H
6
O)
=
drinking alcohol
 
EXAMPLE #3: aspirin  (C
10
H
12
O
5
 )
= 
what to take 
after excess alcohol
 
EXAMPLE #4: glycine  (C
2
H
5
NO
2
)  =amino
acid, building block of proteins (
building
block
 of all living things )
 
EXAMPLE #5:
 
DNA  (
BLUEPRINT
 for all living things)
 
Deoxyribonucleic acid
 
POPULAR
GRAPHIC
FOR DNA
organic chemical notation 
(see also pp 108-109 of text)
3 different ways to read/draw HONC structures
 
1) 
Complete skeletal form
 
All or most all lone pairs,  bonds and
atoms shown explicitly.
Rubbing
alcohol
Aside on organic chemical notation 
(see also pp 108-109 of text)
3 Different ways to read/draw HONC structures
(continued)
 
2) 
Condensed form
 
Methyl (CH
3
) and methylene groups (CH
2
)
written without C-H bonds, but lone pairs
still shown.
 
Complete skeletal form
Aside on organic chemical notation 
(see also pp 108-109 of text)
 
3) Abbreviated bond line form (most
used by organic chemists)
 
All kinks ,  ends and crossings are C. If no other
groups showing,assume H around C to reach 4
bonds to C.  Lone pairs  assumed via HONC
rules(though text doesn’t.)
3 Different ways to read/draw HONC structures
(continued)
 
Complete
Skeletal
 form
Why bond line form is preferred by organic
chemists
 
Complete skeletal form
 
Bond line form
 
SIMPLER
LOOKING IS
PRETTIER
 
 
messy,ugly
I’m neat
&
pretty
aspirin
+ 
more board practice :
complete skeletal
 condensed 
bond line
 bond line 
condensed
 complete skeletal
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Exploring the concept of shared electron bonds focusing on valence electrons, core electrons, Lewis dot structures, and the Lewis Octet Rule. Learn how to apply these rules to build organic compounds and understand the stability of elements through visual representations.


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  1. 1.Whats `shared in a shared electron bond ? Answer: Just the outer shell or `valence electrons of bonding atoms. .. The main `visual : Lewis dots :S: Exercise 2.1

  2. Valence vs `Core electrons How many `core electrons does S have ? 10 (Ne) Inert gas core electrons for S How many total electrons does S have ?16 How many valence electrons does S have ? .. Valence shell or outer shell of S 6 1 2 3 4 5 6 :S: . Dot picture shows only valence electrons

  3. Practice a few.exercise 2.2

  4. 2. What rules govern the number of bonds to the elements and how do we use these rules to build organic (and other non-ionic) compounds ? Uncle `Gil sez: If you can count to 8, even you can do it, maggot .. Gilbert Newton Lewis: (Uncle Gil) American Chemist

  5. Foundations of the `Lewis Octet Rule What we learned From chapter 2: e- Na+ Cl- + Na + Cl (+) and (-)attracted to each other to form ionic bond 11 e- 10 e- 17 e- 18 e- Ar Ne like Ne Like Ar # valence electrons ? 8 8 .. DOT PICTURE VISUAL Lewis `octet is the most stable form of elements all atoms (X) want to look like this,whether ionic or not ionic : [X]: ..

  6. USING THE `OCTET RULE How to build a covalent compound using `Lewis Rules (same process as on pp 102-106 of text. The Lewis Octet Rule 1) Count all the valence electrons on all the bonding elements Ex. CO2 Valence e- on C = 1 x 4 = 4 Valence e- on 2O = 2 x 6 = 12 total valence e- = 4+12= 16

  7. How to build a covalent compound using `Lewis Rules (same process as on pp 102-106 of text) the Lewis Octet Rule (continued) 2)Start by drawing single bonds to each atom and compute the total number of electrons in those. Electrons in bonds= 2 bonds x 2 e-/bonds = 4 Ex. O-C-O

  8. How to build a covalent compound using `Lewis Rules (same process as on pp 102-106 of text) .continued 3) Distribute the remaining valence electrons not in bonds one by one and evenly to each element in the molecule. If an element reaches an `octet , stop placing electrons on it and distribute what s left to the other elements. Electrons not in bonds = 16-4=12 Distribute them evenly among C and O Ex. O-C-O

  9. How to build a covalent compound using `Lewis Rules (same process as on pp 102-106 of text) .continued 4) Check each atom for an octet. If all have octets, you have the right Lewis structure. If not, go back to step 2, include a double bond somewhere and repeat steps 2-4 until a complete octet is achieved around each element assuming the given electron count Ex. O-C-O x x

  10. Step 2 repeat: add another bond x Electrons in bonds = 3 bonds x 2 e-/bonds = 6 O=C-O Skip C now has octet Electrons not in bonds = 16-6 =10 Step 3 repeat: distribute 10 non-bonded electrons evenly Step 4 repeat: check to see if every element has an octet

  11. Back to Step 2 repeat: add another bond x Electrons in bonds = 3 bonds x 2 e-/bonds = 6 O=C-O Skip C now has octet Electrons not in bonds = 16-6 =10 Step 3 repeat: distribute 10 non-bonded electrons evenly (into lone pairs) Step 4 repeat: check to see if every element has an octet

  12. Step 2 repeat repeat: add yet another bond Electrons in bonds = 4 bonds x 2 e-/bonds = 8 Skip C..already has octet O=C=O Electrons not in bonds = 16-8 =8 Step 3 repeat repeat: distribute 8 non-bonded electrons evenly (into lone pairs) Step 4 repeat repeat: check to see if every element has an octet

  13. LEWIS PREDICTION FOR BONDING IN CO2 Lone pair (2 e- per pair): 2 dots = one pair O=C=O Bond pairs (2 e-/bond): one line = 1 bond Some helpful Lewis language: bond pairs vs lone pairs

  14. 2) What rules govern the number of bonds to the elements and how do we use these rules to build organic (and other non-ionic) compounds ? Lewis s Answer: 2. LEWIS (OCTET) RULE

  15. EXERCISE 2. PLAYING THE LEWIS ELECTRON DOT GAME Mole $$ !!!!

  16. ??? Doc s annoying question habit rears it ugly head again .

  17. I am so annoying ??? How do we know what `hooks to what in more complicated molecules ? Examples where confusion can arise: CO2 C-O-O or O-C-O ?? SO2 S-O-O or O-S-O ?? C O O about rings ? What S O O

  18. CO2 SO2 C-O-O or O-C-O ?? S-O-O or O-S-O ?? Simple rule of thumb #1: Elements closer to the center of the Periodic Table tend to be in the center of a molecule

  19. Applying Rule of Thumb 1 to CO2 C is closer to center line=> C in center of CO2C-O-O or O-C-O ?? `center of Table `center line

  20. Applying Rule of Thumb 1 to SO2 S-O-O or O-S-O ?? S is closer to center =>S in center of SO2

  21. What about rings ? Simple rule of thumb #2: C S O O O O Compound structures tend to minimize `strain and maximize bond angles

  22. Docs questions revisited 1.What s `shared in a shared electron bond ? Valence electrons only; 2 per bond 2.What rules govern the number of bonds to the elements and how do we use these rules to build organic (and other non-ionic) compounds ? Lewis Octet Rule + Rules of Thumb 1 and 2 3.How do we `read organic compound formulas and deduce their bond and electron arrangements ? ???

  23. The simple as 1,2,3,4 HONC bonding rules (for organic compounds only) Element bond count to element lone pairs on element H 1 O 2 N 3 C 4 O, N & C BOND COUNT + LONE PAIR COUNT = 4 0 2 1 0 *USE FOR EXERCISE 2.4

  24. Simple Bonding Rules for Organic* compounds: the HONC Rules *Compounds made of C+ H with options to include O and N EXAMPLE #1: ethane (C2H6) = one of the `natural gases H H H C C H H H

  25. EXAMPLE #2: ethanol (C2H6O) =drinking alcohol H H H C C OH H H

  26. EXAMPLE #3: aspirin (C10H12O5 ) = what to take after excess alcohol H OH O C C H H O C H O C C C H C C H C H H C H H H

  27. EXAMPLE #4: glycine (C2H5NO2) =amino acid, building block of proteins (building block of all living things ) H H N H C O H C H O

  28. EXAMPLE #5: DNA (BLUEPRINT for all living things) Deoxyribonucleic acid

  29. POPULAR GRAPHIC FOR DNA

  30. organic chemical notation (see also pp 108-109 of text) 3 different ways to read/draw HONC structures 1) Complete skeletal form H OH H Rubbing alcohol H C C C H H H H All or most all lone pairs, bonds and atoms shown explicitly.

  31. Aside on organic chemical notation (see also pp 108-109 of text) 3 Different ways to read/draw HONC structures (continued) 2) Condensed form OH H OH H H C C C H H3C C CH3 H H H Complete skeletal form H Methyl (CH3) and methylene groups (CH2) written without C-H bonds, but lone pairs still shown.

  32. Aside on organic chemical notation (see also pp 108-109 of text) 3 Different ways to read/draw HONC structures (continued) 3) Abbreviated bond line form (most used by organic chemists) H H OH Complete Skeletal form OH H C C C H H H H All kinks , ends and crossings are C. If no other groups showing,assume H around C to reach 4 bonds to C. Lone pairs assumed via HONC rules(though text doesn t.)

  33. Why bond line form is preferred by organic chemists SIMPLER LOOKING IS PRETTIER OH aspirin O C OH O O O C H H C C C O O C C C H H H C H H Bond line form Complete skeletal form messy,ugly I m neat & pretty

  34. + more board practice : complete skeletal bond line condensed condensed complete skeletal bond line

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