Download pp. 18-21

Lecture 6
Chapter 3
1. What is the mass, in grams, of one molecule of ammonia, NH3?
(a) 17
(e) 3.7 × 10−18
(b) 2.8 × 10−23
(f) 6.0 × 1023
(c) 1.0 × 10−21
(g) 2.8 × 1023
(d) 1.0 × 10−21
HINTS
Calculate the mass of one mole of NH3. How many molecules are in a mole? Use the units to be
sure that you multiply (or divide) correctly.
2. Which one of the following contains the largest number of oxygen atoms?
a)
b)
c)
d)
e)
0.1 mole of KAl(SO4)2•12 H2O
0.2 moles of P4O10
0.3 moles of AgNO3
0.4 moles of H2SO4
0.5 moles of Ca3(PO4)2
HINT
How many moles of oxygen are in each sample?
3. The following substances are fertilizers that contribute nitrogen to the soil: urea [(NH2)2CO];
ammonium nitrate; ammonium sulfate. Arrange these fertilizers in order of decreasing nitrogen
content on a mass percentage basis.
a)
b)
c)
d)
e)
ammonium nitrate > urea > ammonium sulfate
ammonium nitrate > ammonium sulfate > urea
urea ≅ ammonium sulfate ≅ ammonium nitrate
urea > ammonium nitrate > ammonium sulfate
ammonium sulfate ≅ ammonium nitrate > urea
HINTS
What is the formula for ammonium nitrate? for ammonium sulfate? (Do you know the formula and
charge of ammonium ion, nitrate ion and sulfate ion?)
Once you know the formulas, can you do this WITHOUT a calculator?
Summer 2005
- 18 -
Chem 6 Study Guide
Lecture 6
Overview of COVALENT BONDING
To understand covalent bonding at molecular (atomic) level
1. Lewis structures
tell where electrons are (like a census tells where people are).
2. VSEPR theory
shows how to use Lewis structures to predict the shape of a molecule.
3. Valence Bond Theory
explains how covalent bonds are the result of orbital overlap: (σ and π
bonds).
-----------------------------------------------------------------------------
Summer 2005
- 19 -
Chem 6 Study Guide
Lecture 7
Molecular Structure
1. Determine Lewis structure.
2. Use VSEPR to determine electron pair geometry.
(count electron domains: double and triple bonds counted as one
domain!).
3. Use electron pair geometry to determine hybrid orbitals.
4. Determine molecular geometry. Focus on bonded-electron pairs
ONLY to determine the molecular geometry (MG)
5. Is the molecule polar?
To answer this, use knowledge of:
¾ Molecular shape
¾ Bond Polarity
To determine the polarity of a molecule that has more than 2 atoms:
a) find molecular shape (3D)
b) find "bond" dipoles (using electronegativity differences)
c) use vector "analysis" to find net molecular dipole
Summer 2005
- 20 -
Chem 6 Study Guide
Shape, Polarity, Hybrid Orbitals
Lecture 7
Draw Lewis structures for the following molecules. Determine the electron pair geometry and the molecular geometry
for each. (Draw pictures if you want but be sure to include the name of the geometries.) What hybrid orbitals are
used in bonding? Which of these molecules are polar?
Molecular
formula
Lewis
structure
e− pair
geometry
Molecular
geometry
polar?
yes/no
Hybrid
orbitals
NF3
BF3
ClF3
ClO4−
PF5
BrF5
CO2
XeF2
OF2
Summer 2005
- 21 -
Chem 6 Study Guide