Chemistry is a science
. Chemists use the scientific
when they investigate matter. There is no one definition
of scientific method that is applicable to all sciences; however,
the following outline describes an approach that is commonly
used by chemists.
- Observation-a fact or event that we can detect using
- Law-a summary of many similar observations, noting
their common features or trends.
- Hypothesis-a possible explanation for the common feature
- Experiment-laboratory manipulation to test whether
a hypothesis is correct.
- Theory-a hypothesis that has withstood repeated tests
and that is likely to be correct.
Note that these activities are often repeated in a cycle.
An experiment provides us new observations, which may lead us
to revise laws and hypotheses, which may suggest new experiments.
Here is an example of how the scientific method works.
- Observation #1-"carbon oxide" consists of the elements
carbon and oxygen in a 3 : 4 mass ratio.
- Observation #2-another "carbon oxide" contains
carbon and oxygen in a 3 : 8 mass ratio.
- Law-if two compounds contain the same elements but in different
proportions, the ratio of those proportions will be the same
as the ratio of two small whole numbers. (Note: this is
called the law of multiple proportions; it was formulated
by John Dalton in the early 1800's). In our example above, dividing
(3/4) by (3/8) yields (2/1); in other words, compound 2 contains
exactly twice as much oxygen as compound 1.
- Hypothesis #1-each element consists of small, indivisible
particles called atoms.
- Hypothesis #2-each molecule of compound 2 contains two oxygen
atoms (CO2), while compound 1 contains
only one oxygen atom (CO).
- Hypothesis #3-an oxygen atom is 4/3 as massive as a carbon
- Experiments-thousands of compounds were analyzed by hundreds
of chemists throughout Europe. All of the elemental compositions
were consistent with the law of multiple proportions.
- Theory-by the second half of the nineteenth century, most
scientists accepted Dalton's atomic theory as being correct.