Transcript Chapter 1 Introduction: Matter and Measurement

Chemistry, The Central Science, 12th or LSU
edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chapter 1
Introduction:
Matter and Measurement
KR
Matter
And
Measurement
Roadmap:
• Physical Objects (bodies, things)
Matter, RadiationMatter as atoms,
moleculesMatter as electrons,
protons, neutrons….Matter
properties
• Chemistry  Science, Chemistry
interested in structure and change of
matter and its properties
• Science  Practical aspects (units,
Matter
And
conversions)
Measurement
The Chemical View of Things: Matter
• Matter is the physical material
of the universe. It occupies space, has
specific properties (like mass) that can be
observed and measured.
• Matter: Some elementary material objects
(electrons, protons, neutrons) combine to
form elementary substances, atoms of
elements, molecules, ions etc.
• Modern chemistry works at molecular
level.
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Chemistry
In this science we
study matter and the
changes it
undergoes.
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What is Chemistry?
• What chemists often try to do is to find
the relationships between the structure
of matter and the properties of matter
we observe
• Chemistry is the science that seeks to
understand what matter is and what it
does by studying what atoms and
molecules and the subatomic objects
do. In practice, chemistry is different
than physics.
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The Scientific Method
• A process for trying to understand nature
by observing nature and the way it
behaves, and by conducting experiments
to test our ideas.
• Key Characteristics of the Scientific
Method include Observation,
formulation of Hypotheses,
Experimentation and formulation of
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Laws and Theories
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Scientific Method
The scientific method is simply a systematic
approach to solving problems.
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Scientific method- a visual
presentation:
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Laws
• Summary of observations that
combines some past observations
into one general statement about
those observations
– Law of Conservation of Mass – “In a
chemical reaction matter is neither
created nor destroyed.”
• Allows you to predict future
observations
– So you can test the Law with
experiments
• Like in any law, improved
experiments and new knowledge
could indicate violations and/or
extensions of previous scientific
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laws
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CHEMISTRY and CHEMICAL IN
THE USA
•
•
•
•
•
http://www.doe.gov
http://www.nsf.gov
http://www.nist.gov
http://www.epa.gov
http://www.nih.gov
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Units of
Measurement
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What is a Measurement?
• quantitative
observation
• comparison to an
agreed upon
standard
• every measurement
has a number and a
unit
Project: measuring global temperatures
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A Measurement
• the unit tells you what standard you
are comparing your object property
(observable) to
• the number tells you
1.what multiple of the standard the object
measures
2.the uncertainty in the measurement (the
procedure for the estimate of uncertainty
we will see later)
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SI Units
• Système International d’Unités
• Uses a different base unit for each quantity
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Metric System
Prefixes convert the base units into units that
are appropriate for the item being measured.
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Volume
• The most commonly
used metric units for
volume are the liter (L)
and the milliliter (mL).
□ A liter is a cube 1 dm
long on each side.
□ A milliliter is a cube 1 cm
long on each side.
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Uncertainty in Measurements
Different measuring devices have different
uses and different degrees of accuracy.
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Temperature:
A measure of the
average kinetic
energy of the
particles in a
sample.
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Temperature
• In scientific
measurements, the
Celsius and Kelvin
scales are most often
used.
• The Celsius scale is
based on the
properties of water.
□ 0C is the freezing point
of water.
□ 100C is the boiling
point of water.
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Temperature
• The Kelvin is the SI
unit of temperature.
• It is based on the
properties of gases.
• There are no
negative Kelvin
temperatures.
• K = C + 273.15
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Temperature
• The Fahrenheit
scale is not used in
scientific
measurements.
• F = 9/5(C) + 32
• C = 5/9(F − 32)
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Density:
Physical property of a substance
m
d=
V
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Uncertainty in
Measurement
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Estimating the Last Digit
•
for instruments marked
with a scale, you get the
last digit by estimating
between the marks
–
•
if possible
mentally divide the space
into 10 equal spaces, then
estimate how many spaces
over the indicator is
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1.2 grams
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Accuracy versus Precision
• Accuracy refers to the proximity of
a measurement to the true value
of a quantity.
• Precision refers to the proximity of
several measurements to each
other.
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Significant Figures
• The term significant figures refers to
digits that were measured.
• When rounding calculated numbers, we
pay attention to significant figures so we
do not overstate the accuracy of our
answers.
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Significant Figures: use
exponential notation, or
1. All nonzero digits are significant.
2. Zeroes between two significant figures
are themselves significant.
3. Zeroes at the beginning of a number
are never significant.
4. Zeroes at the end of a number are
significant if a decimal point is written
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in the number.
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Significant Figures
• When addition or subtraction is
performed, answers are rounded to the
least significant decimal place.
• When multiplication or division is
performed, answers are rounded to the
number of digits that corresponds to the
least number of significant figures in any
of the numbers used in the calculation.
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Significant Figures
Writing Numbers to Reflect
Precision
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Reporting Measurements
• measurements are written to indicate
the uncertainty in the measurement
• the system of writing measurements we
use is called significant figures
• when writing measurements, all the
digits written are known with certainty
except the last one, which is an
45.872
estimate
estimated
certain
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Dimensional Analysis
• We use dimensional analysis
to convert one quantity to
another.
• Most commonly dimensional
analysis utilizes conversion
factors (e.g., 1 in. = 2.54 cm)
1 in.
2.54 cm
or
2.54 cm
1 in.
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Dimensional Analysis
Use the form of the conversion factor
that puts the sought-for unit in the
numerator.
Given unit 
Conversion factor
desired unit
given unit
 desired unit
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Dimensional Analysis
• For example, to convert 8.00 m to inches,
– convert m to cm
– convert cm to in.
100 cm
1 in.
8.00 m 

 315 in.
1m
2.54 cm
Matter
And
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