- History of Atoms
The Presocratic philosophers of ancient Greece (circ 600--350 BCE) were the first people in recorded history to attempt to understand nature in terms of general principles (AKA general laws or axioms) rather than in terms of a mythology of anthropomorphic gods.But one doesn't what to draw to hard a line.
In many early mythic conceptions, the earliest gods are rather peronalityless and resemble elementary or primeval forces.
This is true of Greek mythology where the earliest god is Chaos is formless or void state from which everything originated---as recounted in Hesiod's (circa late 8th century BCE) poem Theogony.
Caption: "So-called Seneca. Ancient Roman bronze now at the National Archaeological Museum of Naples, Italy." The bust was originally thought to be of Seneca (c. 4 BCE--65 CE). But nowadays the Pseudo-Seneca is considered to possibly be an imagined portrait of Hesiod (circa late 8th century BCE).
Hesiod is the author of the long poems Theogony and Works and Days.
Hesiod as revealed in Works and Days---which not be by Hesiod, but by another Greek of the same name---is a rather gloomy, pessimistic farmer-poet---maybe a lot like Robert Frost (1874--1963)---the bust artist may have been trying to capture that character.
Credit: Ancient Roman sculptor. Image by Massimo Finizio.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Seneca.JPG.
Permission: Licensed under the Creative Commons Attribution ShareAlike 2.5.
Gaia was somehow produced by Chaos and Gaia (Mother Earth) gave birth parthenogenetically to Uranus (Father Sky), and the story goes onto more generations of more personalized gods.
It seems that Hesiod and other mythological thinkers may have already had a rudimentary idea that the universe could NOT have started with quirky personalities.
Nevertheless, a thoroughgoing attempt to study nature from general principles---natural philosphy---starts with the Presocratics.
Caption: "Graphical relationship among the various pre-socratic philosophers and thinkers; red arrows indicate a relationship of opposition."
A flow-chart of the Presocratics.
Credit: User:Tresoldi AKA Tiago Tresoldi.
Image linked to Wikipedia.
Permission: Licensed under the Creative Commons Attribution ShareAlike 2.5.
One must emphasize, the Presocratics did very little experimentation of detailed observation. Their explanations of natural phenomena in terms of their various sets of general principles were vague and handwaving.
The theories of the Presocratics can be described a rational mythmaking.
Still their theories are often fascinating laid a foundation for later science.
The idea of atoms began with the atomism of the shadowy Leucippus (ca. 1st half of 5th century BCE and his much better known student Democritus (ca. 460--ca. 370 BCE)
Caption: "Democritus (ca. 460--ca. 370 BCE) meditating on the seat of the soul (1868) by Leon-Alexandre Delhomme (1841--1893 or 1895)."
Democritus was foremost exponent of atomism among the ancient Greeks
Credit: User:Jean-Louis Lascoux.
Image linked to Wikipedia.
Permission: Use under GNU Free Documentation License.
Ancient atomism is very far from out modern concepts.
The atomists were thinking of minute, absolutely uncutable hard bodies. The word atomos means uncutable. They though dust motes may have been visible atoms.
How the atoms interacted to make the atomists ever came up with the idea of atoms. But perhaps it wasn't so hard. From a simpleminded perspective, one might say there are only two choices: matter is infinitely divisible or it's not. In the later case, some kind of atoms becomes a plausible idea.
The atomists and their followers came up with many ingenious ways to explain in vague ways the universe in terms of atoms.
But they never had solid evidence.
Also atomism fell into disfavor in Greco-Roman antiquity because it was incorporated into Epicureanism which was considered atheistic---actually the Epicureans believed the gods exist, but that they didn't do anything in the human world.
The idea of atoms didn't disappear and in the Scientific Revolution of the 17th century was picked up by, among others, Rene Descartes (1596--1600) and Newton (1643--1727).
But no solid evidence for them was yet known.
Solid evidence appeared with John Dalton (1766--1844) who was able to explain chemistry in terms of the interactions of atoms.
To understand the basics of Dalton's we consider the following example using modern values.
2.0158 grams of hydrogen gas + 15.999 grams of oxygen gas always react together to give 18.015 grams of liquid water.Now hydrogen gas, oxygen gas, and liquid water all seem to be homogeneous substances.No matter how small a sample you take of any (as long as it is macroscopic), the sample's chemical properties are the same.
So let's posit hydrogen consists of atoms of mass 1.0079 atomic mass units (AMUs) and oxygen of atoms of mass 15.999 AMUs.
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The atomic mass unit
is a mass scale approrpiate to atoms.
An atom's mass in AMUs is its atomic mass.
The modern definition of atomic mass unit is the 1/12 of mass of an unperturbed Carbon-12.
The number of AMUs in 1 gram is:
1 gram ---------------------- = Avogadro's number 1 AMU in grams =6.02214179(30)*10**23 = approx 6*10**23 = approx 10**24 = 1 moleDividing any mass of a substance sample by the substance's atomic mass and Avogadro's number gives the number of particles in the sample in moles.
