Chapter 2

In order to talk about the nature of the universe ... I shall take the simple minded view that a theory is just a model of the universe, or a restricted part of it, and a set of rules that relate quantities in the model to observation that we make. It exists in our minds.

Stephen W. Hawking

A Brief History of Time

1

Natural Units – atoms, molecules, moles, and electrons

The fundamental components of materials are called the natural units.

In this Chapter, we explore the material world. Unlike the elusive energy, a material has a mass and occupies a volume. Thus, we can easily recognize a piece of material. Driven by energy, materials undergo constant changes, generating all kinds of phenomena. Natural units participate in these changes, but they themselves remain the same.

Unlike physical and chemical phenomena that involve large quantities of material, nuclear phenomena usually deal with interactions among natural units. Thus, we shall review the investigations on natural units before we introduce any nuclear phenomena.

·  What are natural units?

·  How many kinds of natural units are there?

·  How do natural units make up the material world around us?

·  Have we found the true natural units of the material world?


The spirit of science, including nuclear science, is to dig for the ultimate truth. Looking for the ultimate fundamental natural units of the material world started with philosophical approaches followed by scientific investigations. The digging has gone on for almost 5 thousand years, and the dig continues. Quickly, we review the philosophical approaches and experiments leading to the discovery of chemical elements, atoms, molecules, moles, and electrons in the past.

The search for natural units had a slow start, but the results grow exponentially. Following the discovery of radioactive decay, experiments have revealed not only the structure of atom but also smaller sub-atomic particles such as electrons, protons and neutrons. We accepted them as fundamental natural units of matter for a while, but further investigations revealed that protons and neutrons are composed of several particles. These will be discussed in future chapters.

Whether we have found the ultimate natural units remains to be seen, and I hope you keep a continuous interest on this topic to see its future development.

Philosophical Approaches on the Fundamental Natural Unit of Materials

Ancient people did not have the energy concept, nor did they understand the material world. They did not have concepts to perceive deeper into the material world than what it appeared to their eyes. To them, wood logs burned and disappeared, leaving nothing but a little ash behind. Soil, rock, clay, and sand appeared to be indestructible by fire. Water came from the darkened sky and caused floods and mudslides that kill.

However, some wise men asked fundamental questions and suggested that there are some fundamental components for the material world. Their suggestions were accepted on faith rather than on reason or comprehension.

Philosophical approaches from Oriental and Hellenistic cultures on the fundamental components material are briefly described here. People in the orient believed in the dualism of Yin and Yang whereas Plato proposed the primal substances.

Natural Units of Dualism

With a history of more than 5000 years, the Chinese culture is wide spread, particularly in the orient.

·  What is the ancient Chinese view of the material world?

One of the Chinese classics called I-Ching dominated the ancient Chinese view of the material world. A translation of it is known as Book of Change, which was written during the Chu dynasty (1134-247 BC), in cryptic language, which is used by most fortunetellers as their folly. However, it also has its academic value as a classic. A dominant symbol in the book, the Ultimate (Tai-chi) and the trigrams, is shown here. The Ultimate consists of Yin and Yang, from which everything is derived. Yang is the cosmic male principle and Yin is the cosmic female principle.

Yin and Yang were the suggested natural units of all materials. Yang is represented by a solid line –– whereas Yin by a broken line - -. Combining equal portions of Yang and Yin results in four things. Fu-Hsi showed the formation of eight things when they are divided in three parts each can be Yin or Yang, and he represented them by the tri-grams. When a whole has many parts of Yin and Yang many more things are generated. When a whole has many parts of Yin and Yang more things are generated. Thus, natural units Yin and Yang are the fundamental building blocks of materials.

The dualism of Yin-Yang represents a view of the world that does not distinguish energy from matter. This view still affects the ways many Chinese think, eat, exercise, and live.

For discussion:

1.  What are Yin and Yang?
How can combinations of them generate so many different things or material?

  1. What phenomena cannot be explained by the Yin and Yang dualism?

Plato’s Natural Units

Plato and Aristotle left their postulates regarding the material world in writing. They had no concept of energy, and their postulates did not differentiate matter from energy, like the dualism of Yin and Yang. Their intellectual exercises qualitatively described the changing world, and they dominated the reasoning process for a long time.

·  What are the natural units proposed by Plato?

Plato (427-347 BC) postulated that combinations of four primal substances: air, water, fire, and earth made up all materials. Plato hinted at the fifth unobservable substance, ether or quintessence, but it was not widely known. Thus, he suggested four or five natural units.

In his Timaeus, Plato associated the regular polyhedra with the primal substances: cube with earth, tetrahedron with fire, octahedron with air, icosahedron with water, and dodecahedron with ether. From a geometrical viewpoint, there are five and only five regular polyhedra. He thought these mathematical forms are the ultimate representation of the world. This postulate connected geometrical results with the physical world, a system uniting the (mathematical) minds and the material world. Polyhedra have definite shapes. Size and quantity concepts were not present during his time.

Earth / Water
Cold
Dry / Wet
Hot
Fire / Air

2Four primal substances and four qualities in Aristotle's material world.

Plato's student Aristotle (384-322 BC) examined the ideas of primal substances from the viewpoint of causes and effects. He believed in having a limited number of primal materia, but added four qualities: hot, cold, wet, and dry. In his mind, a combination of these qualities and primal substances caused all the phenomena of the world. The primal materia are connected to the qualities in Aristotle's world, as shown in a diagram here. Little further development was made regarding his qualities in terms of science.

Plato applied his knowledge in geometry to interpret the physical world. Aristotle (Sarton, 1970) took it a step further to explain the changes. These early developments illustrated human desire to know the natural units of the material world.

Plato's doctrine influenced scientific reasoning for almost two thousand years. For example, Angelo Sala (1575-1640) considered fermentation as a regrouping of the primal substance. Daniel Sennert (1572-1627) postulated four kinds of atoms (a concept not of finite size) corresponding to the four primal substances. Few scholares challenged Plato's doctrine until it failed to explain the existence of various kinds of air.

During the period between the 5th and 3rd centuries BC, theories of nature in India and other parts of the world were based on conceptions of materials called fire, wind, water, earth, space, and vitalism (animated atoms). The dualism of love and hate also played a part. However, water, fire, wind and earth were considered as natural units in many cultures, perhaps originated from Plato.

Skill developing problems:

1.   What are the natural units postulated by Plato? How are the primal substances related to modern concept of materials? Give a modern definition to primal substances? (Hint: Some scholars suggested the primal substances were related to solid, liquid, gas, and plasma state of material. A fire is a plasma as we shall see in the chapter on nuclear fusion.)

2.   Describe Aristotle’s material world. How are Aristotle’s qualities related to the modern scientific concepts?

Chemical Elements and Atoms

After the time of Plato and Aristotle, human activities became more and more complicated. Enterprises of alchemists, medicine men, and technologists flourished. Due to their wealth, these people had the leisure to pursue scientific reasoning. Slowly, people acquired the concept of quantity and size through commerce, before they acquired the energy concept.

Attitudes of philosophers began to change. Plato and Aristotle still had influence but they no longer dominated the academic circle. For example, Francis Bacon (1561-1626) introduced methods of fact collection and deduction. R. Descartes (1596-1650) introduced a principle of doubt, accepting nothing that cannot be clearly established to be true. Galileo (1564-1642) invented experimental methods, and other scholars soon use them.

The attitude change in the 16th century made a huge difference in the study of the material world. Technologies such as air pump were available to study air. Various gases were identified, and natural units primal substances is replaced by chemical elements

Gas Identification and Boyle's Concept of Chemical Elements

During the 16th century, sophisticated tools began to emerge. People studied jars of various gases. Results of these studies led scholars to reject Plato's primal substances as natural units. New concepts began to emerge, and the same fundamental question was asked again.

·  What are natural units of material?
How many kinds of units are there?

A Belgian scientist J. B. van Helmont (1580-1644) confirmed that gas generated from burning charcoal was the same as that generated from burning alcohol, but different from air. Thus, there is more than one kind of air (gas).

The rich Englishman Robert Boyle (1627-1691) also experimented with gases and air. He noticed the different properties of various gases (air) produced in his experiments. The behavior of various gases convinced him that fire, air, water, and earth were not natural units of material. He published The Sceptical Chymist in 1661 to demolish the doctrine of primal substances. He used the term element for his natural units and he defined it as follows.

I mean by Elements, as those Chymists that speak plainest do by their Principles, certain Primitive and Simple or perfectly unmingled bodies; which not being made of any other bodies, or of one another, are the Ingredients of which all those call'd perfectly mixt (i.e. compound) Bodies are immediately compounded and into which they are ultimately resolved.

In the 17th century, this was the way scholars wrote and spoke. He considered himself a chemist, and from a chemist's point of view, there must be some natural units based on which all materials are derived. In his mind, these natural units are fundamental substances called element that cannot be decomposed or change by whatever means. From these elements, all other materials in the world must have been made up or derived. He defined the term chemical element or element.

An element is a substance that cannot be decomposed into anything simpler.

Since elements are fundamental components of materials, they are natural units. Unfortunate for Boyle, he had not identified an element as an example. Oxygen was one of the few substance first identified as an element, and its discovery will be given shortly.

By the way, Boyle also discovered the Boyle's law of gases, with the help of his assistant Robert Hooke (1635-1703). Since air pumps were available to them Boyle discovered the pressure-volume relationship of a certain amount of gases at constant temperature. On the social side, Boyle pushed for the formation of the Royal Society of England that had a long lasting effect in promoting scientific activities. He, a scientist, had made an impact on his society for the development of a field he dearly loved.

Skill developing problems:

1.   What evidences can you give to show that air is not a chemical element or primal substance?

2.   How can you show that earth, fire, and water are not chemical elements as defined by Boyle?

Discovery of Oxygen as an Element

Fire occurred frequently in ancient time that led Plato to consider it a primal substance. Questions remain, however.

·  What is fire?
What causes a fire and what really happens in a fire?
How can phenomena related to fire be explained?

While Boyle experimented with gases, German scientist J.J. Becher (1635-1682) studied fire. Becher suggested that combustible material contained an inflammable phlogiston, which was released during burning. After release of phlogiston the material was no longer flammable. He recognized that when metals were burned, the products became heavier, but he could not explain. At the beginning of the 18th century, G.E. Stahl suggested phlogiston a substance with negative mass. When lost, the residue became heavier. He represented metal burning by,

Metal ® residue + phlogiston, (an element with negative weight)

The phlogiston theory of fire was widely accepted for almost a hundred years until the air was intensely studied.

Among many scholars that studied air, J. Priestley (1733-1804) found that nitrous air (actually nitrous oxide NO) reacted with portions of air to produce a water-soluble air. He mixed 2 parts nitrous air and 5 parts ordinary air in a marked vessel that was inverted on top of water. The reaction took place at room temperature, and the product (NO2) dissolved in water. As a result, the water level raised to a level indicating 1/5th (by volume) of the air was consumed. He called the consumed portion good air. Priestly went to Paris in October 1774, revealed his results to Lavoisier, who was very interested in the good air.

Independently C.W. Scheele and J. Priestly made some good air by heating various metal salts. Lavoisier later found that charcoal, diamond, sulfur, phosphorus, mercury, lead, and tin burned in the good air. Many products from the burning produced acids when dissolved in water. These results indicated to him that air was not a single substance. Furthermore, he named the good air oxygen[!!] from the Greek words sxuz, (acid) and gqinomai, (I beget). He further concluded that oxygen was a chemical element as prescribed by Boyle, because it could not be decomposed into simpler things. He denounced the phlogiston theory of fire and Plato's doctrine. He formulated the burning of metal as follows.