Topic 15

The Nature of Matter - I

 

Aristotelian Views

The ancient Greeks settled on the paradigm of all materials being made up of four elements - air, water, fire, earth.

The relative proportions of those elements differed in each object and helped define its likelihood of naturally falling or rising. We talked about this earlier in the semester.

This paradigm also explained the observed transformations objects went through when they were burned.

 

Alternative Greek Views

Democritus (~370 BC) believed that all things are composed of unchangeable atoms, too small to see, each with its own shape and size with intervening empty space.

This idea was, however, untestable at that time and did not explain observed behavior of matter any better than the Aristotelian view. In fact, the Aristotelian view allowed for some level of prediction of motion of behavior during burning based on the relative amount of the four elements.

This idea remained around up to the Renaissance but not believed by many people.

 

View from Technology

While the Greek philosophers were arguing about the nature of matter, another group was making equally important observations and using them for society - the metallurgists.

They knew of copper, tin, iron, gold, silver, electrum (made of gold plus silver), lead, mercury

They were able to mix copper and tin to form bronze and make a primitive form of steel.

These people, however, never wrote down what they did and may not have had much, if any, contact with the Greek philosophers. Another example of Wolpert's view that science and technology did not become intertwined until the 19th century.

 

A New Discipline - Alchemy

During the Middle Ages a group of natural philosophers, called alchemists, developed who thought that materials could be transmuted from one form to another.

The knowledge of alchemy must have come from the Arabs as did much other early science information, transferred by people involved in the Crusades.

A key goal of alchemy was the formation of gold from some other base metal.

To that end, alchemists did a lot of experimentation to determine the properties and characteristics of materials.

Alchemists did publish their work. It shows that they were arguably the first real chemists. They mixed materials together to form other materials and tried to break down materials into their simplest parts.

 

Forms of Matter

By the beginning of the Renaissance, natural philosophers, alchemists, and general observation suggested that all matter had three forms - solid, liquid, gas. (We now know that there is a fourth form - plasma.)

Also, there was another observable -radiation (heat, fire, light, etc.). However there was no clear understanding of what it was - a real material or another form of matter.

 

Methods of Scientific Progress from the Time of the Greeks Until the Renaissance

The nature of matter had to be arrived at by observation as in astronomy or studies of motion.

However, there was no theoretical or mathematical basis for defining the nature of matter, unlike the studies of astronomy or motion.

Unfortunately, the key observables were invisible unlike astronomy or motion studies.

As a consequence, by the beginning of the Renaissance and the time of Copernicus there was a mixture of beliefs. Some still held on to the Aristotelian view, while others knew that there were a variety of natural materials which could not be broken down any further. Even so, there was no new paradigm to explain these natural materials.

 

Rebirth of Atoms

By the beginning of the 19th century, the idea of atoms as the primary constituents of all matter was back in the forefront even though no one had ever seen an atom.

Lavoisier showed that burning elements needed to have oxygen present.

John Dalton viewed chemical reactions as simply the rearrangement of atoms.

 

Table of Elements

By the mid 19th Century most of the natural substances which we now know as elements had been discovered.

The substances were studied to determine their fundamental properties - density, solubility, burnability, ability to react with other substances, etc.

Mendeleev divised a table of substances (elements) which grouped them according to their properties. this eventually became what every school child knows as the Periodic Table of Elements.

 

Mathematics of Matter

Even without being able to see atoms, Newton's Laws could be applied to their motion by treating them as a large statistical assemblage.

This became the field of Statistical Mechanics.

Statistical Mechanics could explain pressure of gases by continuing movement and interaction of atoms like billiard balls colliding. This also helped explain heat conduction as heat energy transferred from one atom to another.

 

The First Direct Observation of Atoms

Einstein (1906) was the first to point out direct evidence for the existence of atoms by explaining Brownian Motion.

Brownian motion was first observed in 1827 - observed that inanimate objects (pollen grains, dust particles) moved sporadically while in water droplets observed under a microscope.

Einstein explained that their motion was caused by water atoms (now molecules) hitting the particles and moving them about. He was able to use statistical mechanics to quantitatively explain the actual motion of the large visible particles as a result of random bombardment of the invisible atoms.

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