The scientific method is a procedure for answering scientific questions in a manner that is reasonably objective. Sources vary with regard to the number and exact nature of the steps in this method; however, four steps are common to all: one, observation; two, formulation; three, prediction; and four, experimentation. Each of these steps is essential.
First, the scientist must observe the phenomenon. It isn’t valid to merely use reason and logic — many statements are logical, but that does not make them true. Aristotle, a student of Plato, is often considered the first true scientist. Plato relied on pure reason, while Aristotle sought an empirical (experiential) foundation for his teachings. His observations of the natural world allowed him to draw conclusions such as the differentiation between marine mammals and fish, the development of chicken embryos (based on breaking the eggs of chickens at different stages), and classifications of living things.
When he evaluated chicken embryos, Aristotle moved further in the steps of the scientific method. After observation, the scientist uses what was observed to formulate a hypothesis, an idea about what is happening. For example, benzene was first determined to be a separate substance when Faraday isolated it from manufactured gas. Subsequent study of its properties caused some confusion among chemists, because they could not explain its 1:1 ratio of carbon to hydrogen. In 1865, Kekul? set forth his hypothesis of a ring structure for benzene, with alternating single and double bonds between the six carbon atoms, based on observation of benzene’s isomers when other elements were substituted for one or two hydrogen atoms.
The next step in the scientific method is prediction. The scientist uses the previously formulated hypothesis to predict what will happen in a given scenario. If a scientist hypothesizes that ants prefer sugars over starches, he or she may predict that, when given a choice between candy and cornmeal, ants will eat the candy. In an example from chemistry history, Lavoisier studied the phlogiston theory of combustion and observed that it did not account for the properties of either the leftover gas or the solid mass of substances after burning. He developed a hypothesis about a gas which he called oxygen, predicting that it would greatly facilitate combustion and respiration. He later experimented with this gas and found that his prediction was correct.
This leads to the fourth step of the scientific method: experimentation. This step must be completed carefully in order to make the results valid with regard to the hypothesis and prediction. For example, in the 1930s, Ir?ne Joliot-Curie and her husband Fr?d?ric Joliot predicted that radioactivity (discovered by Joliot-Curie’s parents) could transform one element into another. By bombarding boron with alpha particles, they were able to create a radioactive isotope of nitrogen. They went on to transform other elements, and in 1935 they were jointly awarded the Nobel Prize in chemistry for their discovery of artificial radioactivity.
These examples from the history of chemistry illustrate the formation and testing of hypotheses. However, concepts may be referred to by other names, including theory, law, and model. These primarily identify how far the scientific community has accepted the idea. Hypotheses are narrowly defined, and imply the need for further research. A model is usually accepted, at least in a general fashion, although some of its details may be contested. It typically attempts to explain structure or processes; for example, Dalton’s atomic theory and the water cycle are actually models. Further acceptance is given to a theory, i.e. the valence bond theory of Lewis, and the term “theory” may be used interchangeably with “law,” i.e. the “laws of nature.” But even laws may not be applicable in all circumstances. For instance, Charles’ gas law, which states the relationship between volume of a gas and its temperature, does not apply at very low temperatures. Otherwise, the “law” would imply that the gas volume goes to zero at 0 K.