1. Module 1: Units, Conversions and Representations of Matter
General Chemistry Chem2331

2. Chem 2331: General Chemistry
Outline
Module 1. Video 1.
Representations in Chemistry
Exponential and scientific notations
Metric and SI system
Conversion between metric system
Linear conversions
Square conversions (surface)
Cube conversions
Conversion of combined units: density
Chem 2331: General Chemistry

3. Representations in Chemistry
We can’t see the atomic world.
Too small, too fast. We need representations.
H2O
Experienced with senses mass, density, concentration, pH, T
Qualitative: Diagrams or graphs
We need pictures to understand
Quantitative:
Numbers and letters
Atomic
(submicroscopic)
Macroscopic
Symbolic
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Bibligraphy:
Prof. Hoffmann’s article:
Multiple Representations in Chemical Education
 (Introduction and Chp. 1)
Chem 2331: General Chemistry

4. Representations in Chemistry
The symbolic language can express both, macroscopic and sub-microscopic phenomena
H2O(l)  H2O(s)
macro
NaCl(s) + H2O(l)  NaCl(aq)
H2O  H+ + OH-
sub-micro
Na-Cl + H2O  Na-Cl-OH2
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Chem 2331: General Chemistry

5. Representations in Chemistry
We have many ways to represent the submicroscopic world:
Draw a submicroscopic representation of
1-chloropropane
In organic chemistry there’s a grey area between symbolic and submicroscopic
Chem 2331: General Chemistry

6. Exponential and Scientific Notation
Fixed Decimal or fixed notation:
A drop of water contains about 1,520,000,000,000,000,000,000 molecules.
An atom of neon has a radius of about centimeters.
Exponential notation:
A drop of water contains about 1.52 x 1021 molecules.
An atom of neon gas has a radius of about 7.0 x 10-9 centimeters.
Calculators don’t use superscript. Instead they use E:
A drop of water contains about 1.52E21 molecules.
An atom of neon gas has a radius of about 7.0E-9 centimeters.
Scientific notation: a particular case of exponential notation
In scientific notation, the decimal point in the significant must be after the first digit that is not a zero.
x 1023 = x = 1.52 x 1021 = 15.2 x 1020 = x 1019
Chem 2331: General Chemistry

7. Chem 2331: General Chemistry
Review
3x10-5 * 3*105 =
3x *105 =
3x10-5 / 3x105 =
Chem 2331: General Chemistry

8. The Metric System and SI units
SI Base Units are a selection of the metric units
Physical Quantity (Dimension)
Unit Abbreviation
Unit Name
mass
kilogram kg
length
meter m
time
second s
temperature
kelvin K
electric current
ampere A
amount of substance
mole
mol
luminous intensity
candela cd
Chem 2331: General Chemistry

9. Chem 2331: General Chemistry
Metric prefixes
Scientific Notation and Prefixes
Activity: A typical ballpoint pen is 15 cm long. How long is this in meters and in millimeters (mm) and in micrometers (mm)?
Chem 2331: General Chemistry

10. Conversion Factors between the metric system
A pack of 10 pairs of socks cost $3
How much does 2 pairs of socks cost?
Write this calculation using factor conversion
Using units as a guide to problem solving is called dimensional analysis
You can do the same kind of operations on units as you can with numbers
2cm × 3cm = 2x3 cm2 = 6 cm2
2cm + 3cm = 5cm
2cm ÷ 3cm = 0.66 (no units)
Chem 2331: General Chemistry

11. Conversion Factors between the metric system
Conversion between the metric system
Convert 10-3 kg into mg
Chem 2331: General Chemistry

12. Conversion Factors between the metric system
Length
In m
1x103
=1km
1x102
=1hm
1x101
=1dam
1x100
=1m
1x10-1
=1dm
1x10-2
=1cm
1x10-3
=1mm
1x10-4
1x10-5
1x10-6
Surface
In m2
1x106
=1km2
1x104
=1hm2
1x102
=1dam2
1x100
=1m2
1x10-2
=1dm2
1x10-4
=1cm2
1x10-6
=1mm2
1x10-8
1x10-10
1x10-12
Volume
In m3
1x109
=1km3
1x106
=1hm3
1x103
=1dam3
1x100
=1m3
1x10-3
=1dm3
1x10-6
=1cm3
1x10-9
=1mm3
1x10-12
1x10-15
1x10-18
= 1 L
= 1 mL
Chem 2331: General Chemistry

13. Conversion Factors between the metric system
Convert 2 cm2 into m2:
Convert 10-3 dm3 into mm3
Chem 2331: General Chemistry

14. Conversion of combined units.
Density: mass / volume
Convert 2 g/mL into mg/m3
Chem 2331: General Chemistry