SCH4C
Lewis Structures
Ionic compounds consist of networks or
“crystals” of oppositely charged ions. The
can be represented using Lewis dot
diagrams where the metal loses electrons
and the non-metal gains electrons, creating
charged ions.
Molecular compounds (containing covalent or polar covalent bonds) are
more complex. Lewis structures are usually used to represent the bonding in
these compounds.
In Lewis structures:
 Lines represent shared pairs of bonded electrons.
 Dots are used to represent non bonded valence electrons (usually in pairs)
 Atoms usually bond to create a full valence shell or “stable octet”. This
is called the octet rule.
Bonding Capacity
 Bonding capacity indicates the number of covalent bonds an element can
normally form. There are some exceptions to these values, however.
Group
Electron Dot
Diagram
Bonding
Capacity
1
2
13
14
15
How to draw a Lewis structure:
Step 1: Draw the Lewis dot diagram of the atoms.
Draw each atom, showing only the valence electrons.
Step 2: Arrange Shared Electron Pairs Using the Octet Rule
Arrange electrons so that at least 1 pair is shared and they are
surrounded by a total of 8 electrons (or 2 for hydrogen).
Step 3: Represent the Shared Pairs as Lines
The shared pair (covalent bond) is shown as a line.
16
17
Hints for Making Lewis Structures:
 Consider the bonding capacity of each atom, and make sure you do not
have more than that number of bonds (if possible).
 Make your molecule as symmetrical (balanced) as possible (e.g. O-C-O
instead of C-O-O for carbon dioxide!)
 Hydrogen can ONLY form one bond.
 Oxygen always needs two bonds.
 Carbon ALMOST ALWAYS forms a total of four bonds.
 Substances containing single (unpaired) electrons are highly reactive.
These are known as free radicals. Avoid leaving making a free radical in
the Lewis structure if possible.
Double and Triple Bonds
 Bonded atoms can share 1, 2 or 3 pairs of electrons. These are known
as single, double and triple bonds.
Cl2
O2
PH3
N2
C2H2
N2F2
SCH4C
COVALENT AND POLAR COVALENT BONDING
LEWIS STRUCTURES WORKSHEET
PART A
Each of the following molecules contain only single bonds between atoms.
i) Predict the structure by comparing the bonding capacity of the atoms.
ii) Draw the Lewis Structure for each molecule.
a) Cl2
f) HCl
k) CHCl3
p) CBr4
b) ICl
g) CH4
l) S2Cl2
q) P2H4
c) H2O
h) NF3
m) Br2
r) CF2Cl2
d) PH3
i) Cl2O
n) SiF4
s) SeCl2
e) H2S2
j) C2H6
o) PCl3
t) C3H8
PART B
Each of the following molecules may contain single, double or triple bonds.
i) Predict the structure by comparing the bonding capacity of the atoms.
ii) Draw the Lewis Structure for each molecule.
1) CS2
8) N2F4
15) SiO2
2) HCN
9) O2
16) N2H2
3) BrCl
10) NCl3
17) OF2
4) C2F2
11) H2S
18) C2FCl
5) HI
12) CH3Cl
19) C2Br2
6) CH2O
13) C2F4
20) BF3
7) C2F6
14) C4H10
CHALLENGES:
Try to create a Lewis structure for these ones
1) methanol (CH3OH)
(a poisonous alcohol)
2) cyclobutane (C4H8)
(a circular hydrocarbon)
3) acetic acid (CH3COOH)
(the sour taste in vinegar)
4) glycerol (C3H8O3) (Hint: 3 O-H bonds)
(derived from fats and used in soaps)