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Chemistry

Basic Concepts in Chemistry
The Scientific Method

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WebLecture

Basic Concepts: Types of Matter

Outline

A few cautionary remarks on the Scientific Method

Let's consider, for a moment, the nature of scientific thought, that is, how scientists think about the world around them. In chemistry, we deal with abstractions and generalizations such as "atoms are spherical matter" or "all ionic bonds act the same way way", and we try to reduce all kinds of events to mathematical or geometrical descriptions. This method of abstracting an event from the real world has its origin in the philosophical investigations of the Ionian philosophers of Greece, six hundred years before Christ was born. They wanted to know what matter was — not just this or that particular lump of matter, but the essential set of characteristics (maybe just one) that distinguishes matter from non-matter. They saw all change as a movement from one state to another, and wondered whether the movement of stars across the heavens each night had anything to do with the slow movement of plants toward the sun, water toward the sea, or man toward death. They saw patterns in many natural events, and came to the conclusion that all regular repeatable events should have identifiable causes. When the precipitating event occurs (the cause), the dependent event occurs (the effect), not just sometimes, but every time. For a given set of events, then, the questions become "Why does this happen? What is the cause? Is there more than one cause?" And ultimately, we reach the question "Can we control the cause to control the event?", an question which leads us directly into the practice of technology and its implications.

This view of nature found ready acceptance by many of the Christian Church Fathers of the first four centuries of the modern era. The Judeo-Christian tradition was founded in the concept of law, not just the moral or natural laws that governed human behavior and which were codified in the Torah, but the physical laws that were embedded in the very nature of the created world. If nature follows God's design, it is innately ordered, and that order can be discovered by the human mind. Not only is it a satisfying pursuit for human curiosity, but it is a worthwhile pursuit, as the natural order demonstrates what Dorothy Sayers called "The Mind of the Maker": creation tells us something about God, and studying nature becomes a Christian duty.

[In all fairness, we must report that there was a dissenting opinion that preoccupation with nature or with philosophy distracted one from the proper study of salvation. But this history of science is a topic for a different course.]

The process of science described in many science texts is a simplification of a method which Galileo used to investigate motion in the 17th century. According to this method, a scientist observes some phenomenon, and devises a hypothesis to describe what is happening. A key feature of his hypothesis is a prediction about what will happen under specified circumstances. The scientist then designs an experiment, eliminating all irrelevant conditions, forces, or influences, and tests whether his hypothesis works to predict the experimental outcome. If it works, he may use it to predict further events in similar situations, and continue testing and refining the hypothesis. If it doesn't work, he will use the experimental evidence to modify the hypothesis, and try again. An elaborate and detailed hypothesis which survives many tests and describes a wide range of phenomena becomes a theory, and if it is not disproved over time, the theory may take on the force of a physical law — a description which is largely accepted and unquestioned by the human community.

In this version of the ideal scientific method, a theory can never be absolutely proven to be true. It describes an actual event, which has an objective reality, but the theory itself can be defective or inadequate in its description. It is accepted because it has not yet been disproven, but the acceptance is always provisional. As long as no exceptions occur which cannot be explained as problems of error in measurement, or inability to eliminate all interfering factors (such as friction in motion experiments), the theory is acceptable. In Plato's phrase, it saves the appearances, or accounts for everything it is supposed to cover. However, if unexplained exceptions occur, or new phenomena are observed which the theory cannot describe, it will be replaced by a better theory.

What happens when two competing theories both save the appearances adequately? Scientists generally choose the simpler explanation, where simple is a subjective judgment. This method is based on Occam's Razor, the idea proposed by William Occam in the 14th century, which is don't multiply hypotheses when putting together a theory. In other words, the simplest explanation is usually the best one. If nothing else, it is generally easier to use.

The study of theory replacement is the concern of the history of science, and if you are interested, you may want to read Thomas Kuhn's The Nature of Scientific Revolutions, a recent important work which defines some of the major questions in identifying how and why scientists change their allegiance to a given theory for another.

Scientists like to claim that they follow the experimental method and manage to eliminate errors and depend solely on logical and rational examination of observation. In reality, scientists have their favorite theories, and are under many non-scientific pressures which often dictate what they will study and how they will make observations, take surveys, or perform experiments. Karl Popper, who is an historian of science, found in his interviews with British scientists in the 1950s that they often had a very good idea of what their experiments ought to prove, and designed them accordingly. An objective observer might think there is quite a lot of difference between trying to find a way to support a given hypothesis, and trying to test which of two equally interesting hypotheses does a better job of explaining the phenomena. More recently, some astronomers claimed that a rock (which they believe originated on Mars, not Earth) shows signs of ancient bacterial life. Since government funding is a limited resource, such a claim, and the resulting media interest, might well sway policy makers to fund another mission to Mars rather than put more money in the space station, with direct implications for the types of research that can be done, the technological instruments that will be developed, and the number of ex-NASA employees working as gas station attendants in Pasadena, CA, where the unmanned missions are planned and run, and Huntsville, AL, where the space station is being developed.

Keep these questions in mind about science in general, and chemistry in particular:

[I use the generic he throughout my lectures for grammatical simplicity only; I would personally take serious exception to the idea that women can't be good scientists!]

A little background: Types of Matter

As chemists, we worry only about solids, liquids, and gasses, and how elements in one combination or set of relationships recombine to form a different set of relationships. The fourth and fifth states of matter, plasma (found at the centers of some stars, where atoms are mushed together under tremendous pressure and the electron shell collapses) and Bose-Einstein states (supercooled mater, like liquid hydrogen near absolute zero) are primarily of interest to physicists.

Pure substance is a concept that goes back to ancient times (possibly to metallurgists and coin minters, who had to guarantee the value of their goods). The ancient Greeks struggled for centuries to define matter and describe its characteristics. According to Aristotle (300 BC), his predecessor Thales of Miletus (c. 600 BC) claimed that everything was made of water, by which he meant a fluid substance, not necessarily the chemical water. Anaximenes (c. 570 BC) favored air, by which he meant something alive. Heraclitus (c. 500) proposed the fire as the origin and image of all things, because it was constantly changing. Leucippus and Democritus (c. 470) together developed the concept that mater was composed of individual small particles which were indivisible (a toma means "without being cut apart") and indestructible. Empedocles (c 470) proposed a system of four elements: earth, fire, water, and air, which interacted through four qualities: hot, cold, wet, and dry.

Empedocles Elements

Empedocles' system won out, because no one could actually observe Democritus' atoms, and because Aristotle and his successors came up with all kinds of combinations of substances that accounted for medical and psychological behaviors. Mercury, for example, was a specific combination of earth and water, which accounted for its heaviness and fluidity. It wasn't until the Renaissance that the definition of matter and identification of elements was seriously challenged, and not until the 19th century that chemists were able to formulate an atomic theory of small particles with unique characteristics. In this century, we have discovered that for our theories to account for all the phenomena we observe, atoms can be neither indivisible or indestructible. Our current definition of matter (that which has mass and occupies space) is an extension of the Greek search for the essential qualities that characterize things with substance. Modern physicists are still trying to identify characteristics they can use to describe the components of atoms.

Click on the colored bars for more about each aspect of matter shown below, or page through the presentation by using the grey button at the bottom of each screen.

Practice with the Concepts

Compounds and atoms.

Make sure that you understand how to read a chemical formula for a molecule.

CH3CO2H has how many carbon atoms? how many hydrogen atoms?

Discussion Questions

Optional Readings

The scientific method is only part of the practice of "real" science. There are a number of unwritten rules that govern how scientists chose, conduct, and publish their research. You might want to check out the Ethics in Science site for essays on proper conduct of scientific research, particularly in the area of chemistry. What in particular supports or contradicts the Judeo-Christian assumption that nature is a created entity with objective reality that can be known?