Chemistry I: Bonding and Intermolecular Attraction Notes
1)
Covalent Bonding: Lewis Structures
a) Review
What is the Lewis dot diagram of:
N
N3-
S
S2-
I
I-
b) Write the Lewis dot structures for the following:
c)
F2
H2 O
NH3
O2
H2
HI
N2
CO2
ONCl
ICl3
BeCl2
BF3
Instructions for writing Lewis structures
i) Count up the valence electrons. You can’t use any more than this number of electrons!
ii) Arrange the atoms: C often goes in the center, H never goes in the center, the center atom is often
written first
iii) Single bond all the outer atoms to the center atom, using 1 electron pair per bond
iv) Using unshared pairs, give the outer atoms octets.
v) Give the center atom the rest of the electrons as unshared pairs.
vi) Check to see if the center atom has the octet
(1) Exception: group II elements do not form the octet; they get a total of 4 electrons
(2) Exception: group III elements do not form the octet; they get a total of 6 electrons
(3) If the center atom has more than 8 valence electrons, then that’s okay. This is called “octet
expansion”
(4) If the center atom has fewer than 8 valence electrons, remove unshared pairs from the outer
electrons, and form double or triple bonds
2)
Orbital Box Overlap Diagrams: a way to represent bonding, using orbital box diagrams
Use the orbital box diagrams of only the bonding electrons!
Examples: Draw the Lewis dot and orbital box diagrams for the following molecules:
a) NF3
e) Cl3 CCCl3
b) HOBr
f)
c)
g) BeH2
ClNNCl
d) CH4
3)
h) BCl3
Resonance:
Examples: Draw the Lewis dot structures for the following, and include resonance forms
a) CO3 2d) SO3
b) HCO3 -(the H is attached to an O)
4)
Br2 CCBr2
c) NO2 Odd # of electrons:
ex. NO2
e)
SCN-
Covalent Bonding: Molecular Shapes: VSEPR Model
0
2
0
1
1
3
0
2
1
4
0
3
1
2
2
Name of Shape
1
Drawing
(indicate angles
and any
distortions)
# Unshared Pairs
VSEPR: Valence Shell Electron Pair Repulsion:
# Bonded Atoms
5)
# Unshared Pairs
3
5
0
4
1
3
2
2
3
6
0
5
1
4
2
Name of Shape
Drawing
(indicate angles
and any
distortions)
# Bonded Atoms
1
6)
Polarity
a)
Polar Bonds:
b) Polar Molecules:
c)
Sample Problems:
i) Predict which bond in each of the following groups will be the most polar:
(1) C-H, Si-H, Sn-H
(2) Al-Br, Ga-Br, In-Br, Tl-Br
(3) C-O, Si-O
(4) O-F, O-Cl
ii) Which of the following molecules are polar? HCN, HCCH, IF5 , SF4 , Cl2 CCH2
7)
Properties of Substances:
a)
Molecular Compounds
i)
Polar Covalent Molecules
Examples: H2 O, PF3 , CHCl3 …
(1) Intermolecular Attraction:
(2) What does this mean about polarity and melting/boiling point?
(3) Special type of dipole/dipole attraction: Hydrogen Bonding:
Why is the phrase “hydrogen bonding” a misnomer?
ii) Nonpolar Covalent Molecules
Examples: N2 , H2 , CCl4
(1) Intermolecular Attraction:
(2) What does this mean about size and melting/boiling point?
(3) How does the melting/boiling point of nonpolar compounds compare with that of polar
compounds?
iii) Network Covalent Compounds
Describe network covalent structure:
Examples
(1) C(diamond)
(2) C(graphite)
b) Ionic Compounds
How does the melting/boiling point of ionic compounds compare with covalent compounds? Why?
c)
Polarity and Solubility
”Like dissolves like”: What does this catch phrase mean?
Sample Problem:
Will the following solutes (written on top of the table) dissolve in the following solvents (written on the left
side of the table)?
SOLUTESà
SOLVENTS
↓
H3 CCH2 CH2 CH3
H3 CCH2 CH2 CH2 OH
H2 O
CCl4
H3 CCH2 CH2 OH
KCl
d) Metals
Model for Metal Bonding:
e)
Important questions:
i)
Fill in the chart, and explain:
Under what circumstances do the following types of compounds conduct electricity?
Solid
Molecular
Ionic
Metallic
Explain
Liquid
In Solution