1. Chemistry: An Introduction

2. Chemistry: An Introduction
A process of scientific inquiry
Make observations
Qualitative or quantitative
Formulate a hypothesis
Possible explanation
Use “if  then” statements
Perform experiments
Collect data
Analyze data
Form a conclusion
Does the data support the hypothesis, is it valid?
Accept/reject hypothesis

3. Chemistry: An Introduction
Scientific Models
Once a set of hypotheses agree with data/observations, they are assembled in a theory
Also called a model
“A set of well-tested hypotheses that explain a natural phenomenon.”
It is important to distinguish between observations and theories
Observations are witnessed and recorded
Theories are interpretations of the observations
Provide a possible explanation of why nature behaves in a certain way
Theories change as new information becomes available

4. Chemistry: An Introduction
Natural laws
A statement that expresses generally observed behavior
Often the same observation applies to many different systems
Example: the law of conservation of mass – total mass is not affected by chemical changes
A natural law is a summary of observed/measurable behavior, whereas a theory (model) is an attempt to explain what is happening
It is important to note that scientists are human
They have prejudices, they misinterpret data, they can lose their objectivity, they can be affected by politics, money, religion, etc.
The scientific method is only as effective as those who use it

5. Chemistry: An Introduction
Qualitative measurements give results in a descriptive, non-numerical form
Example: cloudy, heavy, soft, yellow
Quantitative measurements give results in a definite form, usually as numbers and units.
Example: 6 moles, 2.3 0C, 8.9 mm3, 5.1 g/mL
Scientific notation is written as the product of 2 numbers
A coefficient and 10 raised to a power
Multiply or divide the coefficients then add or subtract the exponents
To add or subtract – the exponents must be the same

6. Chemistry: An Introduction
SI Units
Le System International is the accepted system of units used by all scientists
Based on the metric system
Prefixes are used to change the size of units.
Derived units: area, dry volume, density

7. Common SI Units

8. Metric Prefixes

9. Chemistry: An Introduction
Uncertainty in measurements
Any measurement has some degree of uncertainty
Depends on the precision of the measuring device
Scientists usually report all certain digits and the first uncertain digit (the estimated digit)
These are known as significant figures
Significant figures are used by scientists to report data

10. Significant Figures
There are three rules on determining how many significant figures are in a number:
Non-zero digits are always significant.
Any zeros between two significant digits are significant.
A final zero or trailing zeros in the decimal portion ONLY are significant.

11. Ch. 1 Chemistry: An Introduction
Precision and accuracy
Terms used to describe the reliability of measurements
Accuracy refers to the agreement of a measured value with a true/accepted value
Precision refers to the degree of agreement among several measurements of the same value (is the measurement reproducible)
There are two types of errors
A random error (indeterminate error) means that a measurement has an equal probability of being high or low (occurs in estimation)
A systematic error (determinate error) occurs in the same direction each time (see page 12, Figure 1.1)

12. Ch. 1 Chemistry: An Introduction
Review:
Rules for counting significant figures
Rules for significant figures in mathematical operations
Rules for rounding
Exponential notation

13. Ch. 1 Chemistry: An Introduction
Temperature is a measure of the average kinetic energy of particles in matter
The temperature of an object determines the direction of heat transfer
Temperature
There are three widely used systems for measuring temperature:
Celsius scale (physical science)
Kelvin scale (physical science)
Fahrenheit scale (engineering science)
Temperature conversions
0C = x (0F - 32)
0F = (1.8 x 0C) + 32
K = 0C

14. Ch. 1 Chemistry: An Introduction
Temperature
Absolute zero is the lowest possible temperature where nothing could be colder, and no heat energy remains in a substance.
Absolute zero is the point at which molecules do not move (relative to the rest of the body)
It is a theoretical limit and cannot be achieved.
By international agreement, absolute zero is defined as precisely 0 K on the Kelvin scale, and − °C on the Celsius (centigrade) scale.

15. Ch. 1 Chemistry: An Introduction
A property of matter often used for identify chemical substances
Density = mass / volume
Common units of density:
g/cm3
g/mL
Specific gravity is the comparison of the density of a substance with the density of a reference substance, usually at the same temperature
Water is commonly used as the reference substance