Name
Date
Period
In Class
Bonding Unit
Homework
Molecular Formulas and Lewis Structures
Electronegativity: a measure of an atom’s tendency to attract shared electrons to itself in a molecule
Molecular compound: compound composed of only nonmetals
Covalent bond: a bond between two nonmetals in which electrons are shared by atoms
Octet rule: atoms tend to be most stable when their valence sublevels are filled; 8 valence electrons
How to draw Lewis structures for molecular (covalent) compounds. (Please fill in, the space below, the directions that
were on the video guide).
1.
2.
3.
4.
FC = valence electrons - # of bonds – lone electrons
in other words, formal charge = valence – sticks – dots
H
2.20
Li
0.98
Na
0.93
K
0.82
Rb
0.82
Cs
0.79
Fr
0.70
Be
1.57
Mg
1.31
Ca
1.00
Sr
0.95
Ba
0.89
Ra
0.90
B
2.04
Al
1.61
Sc
Ti
V
Cr
Mn Fe
Co
Ni
Cu
Zn
Ga
1.36 1.54 1.63 1.66 1.55 1.83 1.88 1.91 1.90 1.65 1.81
Y
Zr
Nb
Mo Tc
Ru
Rb
Pd
Ag
Cd
In
1.22 1.33 1.60 2.16 1.90 2.20 2.28 2.20 1.93 1.69 1.78
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
1.10 1.30 1.50 2.36 1.90 2.20 2.20 2.28 2.54 2.00 2.04
Ac
1.10
C
2.55
Si
1.90
Ge
2.01
Sn
1.96
Pb
2.33
N
3.04
P
2.19
As
2.18
Sb
2.05
Bi
2.02
O
3.44
S
2.58
Se
2.55
Te
2.10
Po
2.00
F
3.98
Cl
3.16
Br
2.96
I
2.66
At
2.20
Kr
3.0
Xe
2.6
Rn
2.4
On your own paper:
1. Draw Lewis structures that obey the octet rule for each of the following:
a. HCN
e. H2CO
b. PH3
f. SeF2
c. CHCl3
g. O2
d. ammonium
h. HBr
2. Which is the better structure of the 2 Lewis Dot diagrams in the following molecules? Show proof in
available space!
BCl3
BCl3
SO2
SO2
IF5
IF5
N2
N2
2
HCO2-
HCO2-
SO4-2
SO4-2
3. Draw Lewis structures for each of the following:
a. POCl3, XeO4, phosphate, perchlorate
b. NF3, phosphite, chlorate
c. Chlorite, SCl2, PCl24. Draw Lewis structures for the following molecules or ions, which have central atoms that do not obey the octet rule:
a. PF5
e. SF4
b. BeH2
f. XeF4
c. BH3
g. ClF5
d. Br3h. SF6
5. ClF3 and BrF3 are both used to fluorinate uranium to produce UF6 in the processing of nuclear fuel. Draw Lewis
structures for ClF3 and BrF3.
6. Draw Lewis structures for the following:
a. BF2Br
b. SiO2
c. CF4
d. TeH2
e.
f.
g.
h.
3
AlH3
CH3Cl
BBr3
SCN-
RESONANCE STRUCTURES
A way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding
cannot be expressed by one single Lewis formula. A molecule or ion with such delocalized electrons is
represented by several contributing structures also called resonance structures. In other words, resonance
structure is an alternate way of drawing a Lewis dot structure for a compound.
7. Draw the resonance structure for each molecule:
a. ClO3-
b. Nitrate
c. O3
d. Carbonate
4
Molecular Geometry Guide:
AXE Method
Molecule
Type
Steric
number
Hybridiz
a-tion
AX2
2
AX2E1
KEY:
A = Central Atom
X = Surrounding Atom(s)
E = # of lone pairs around central atom
Electronic
arrangement
(w/ lone pairs)
Shape
name
Bond
angle
sp
Linear
180°
3
sp2
Bent
120°
AX3
3
sp2
Trigonal
Planar
120°
AX2E2
4
sp3
Bent
109°
AX3E1
4
sp3
Trigonal
Pyramidal
109°
AX4
4
sp3
Tetrahedral
109.°
AX2E3
5
sp3d
Linear
180°
5
Example
s
AX3E2
5
sp3d
T-shaped
90°
AX4E1
5
sp3d
Seesaw
120°
90°
AX5
5
sp3d
Trigonal
90°
Bipyramidal 120°
AX4E2
6
sp3d2
Square
Planar
90°
AX5E1
6
sp3d2
Square
Pyramidal
90°
AX6
6
sp3d2
Octahedral
90°
VSPER THEORY: The geometric arrangement of terminal atoms, or groups of atoms about a central atom in a covalent
compound, or charged ion, is determined solely by the repulsions between electron pairs present in the valence shell of the
central atom. In other words, because of electron repulsion atoms in a molecule or compound want to be as far from each
other as possible.
6
Molecule
BeH2
BH3
NO2‫־‬
CH4
NH3
H2 O
PCl5
Lewis Structure
# Atoms
Attached
# Lone
Pairs
Steric
Number
Hybridization
Actual Shape
Shape Name
Bond Angles
Molecule
Lewis Structure
# Atoms
Attached
# Lone
Pairs
Steric
Number
Hybridization
SF4
ClF3
I3‫־‬
SF6
XeOF4
XeF4
8
Actual Shape
Shape Name
Bond Angles
POLARITY
Polar = difference in electronegativity between two bonded atoms
 Evaluate each bond individually. Use arrows to indicate where the charge is. Imagine you are the
central atom. Will you move?
BF3
BClF2
XeO4
NH3
PCl5
PCl4F
Fun With Molecules!
You have the following molecules:
XeO3, BeCl2, XeF4, PCl5F-, NO3-
A scientist gave these molecules pet names and left clues for his lab aids to identify them. Use the clues to
figure out which name corresponds to each molecule. You might guess these molecules, but you’ll need more
than the names to please this scientist. On a separate page, (i) Show the most stable structure (ii) Determine
shape (iii) Determine molecular polarity (iv) Determine bond angles (v) Write the “name” of the molecules.
 “Billy” used to be nicknamed after the sea villain in “The Little Mermaid.”
 “Davey” has never been in charge, but he’s very willing to wait his turn in line.
 Though “Puck” can be negative and two-dimensional, he resonates well.
 “Sarah” is really noble at heart, but she’s just too square for my tastes.
 Don’t you think “Milo” looks like a tricycle? Hmm. Let’s take a pole or something.