Early Atomic Theories

Thoughts of Existence Pave the Way for Atoms

The ancient Greek philosophers played a significant role in shaping the initial thoughts about atoms and early atomic theories. Several of the ancient philosophers pondered and developed a theory of matter, with one even imagining the existence of a fundamental building block that made up not only all living and nonliving things, but the supernatural as well. Their thoughts were speculative and philosophical, rather than scientific in nature. And while they attempted to touch on the nature of matter and its composition, their real goal was to address something of profound concern to the ancient Greeks: the nature of permanency and change. Unfortunately, these “theories” of matter were rather short-lived. Although there was some revival during the Middle Ages and the Renaissance, they never gained any real momentum until the seventeenth century.
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Einstein’s Paper on Brownian Motion

In 1905, a young Albert Einstein wrote a paper (while working as a patent clerk) on a well-known physical phenomenon of the time, Brownian motion, which had first been noted in 1827. Einstein’s theory correctly described Brownian motion, and at the heart of his theory was the existence of atoms that were in constant motion.



Avogadro and His Number

Avogadro’s Hypothesis

In 1811, Amedeo Avogadro (1776–1856) (born Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto) looked at Gay-Lussac’s results and concluded that when they are at the same temperature and pressure, equal volumes of gas (like two balloons of the same size) contain the same number of “particles.” These particles can be individual atoms, molecules, or even a mixture thereof.

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The Speed of Atoms and Kinetic Theory

James Clerk Maxwell

James Clerk Maxwell (1831–1879) was born in Edinburgh, Scotland, in 1831. His family moved to a small country estate in Middlebie, Galloway (southwestern Scotland) that his father, John Clerk inherited (the addition of the name “Maxwell” was required to satisfy legalities of this inheritance). When he was eight, James’ mother died, of abdominal cancer; she was forty-eight. John Clerk Maxwell was an attentive and perhaps overly protective father. Unfortunately, he made the mistake of entrusting James early education to a tutor who employed beatings as a teaching tactic. Fortunately, a visit from his maternal aunt, Jane Cay, discontinued this abusive treatment, as she was able to convince Maxwell’s father to allow him to continue his education at Edinburgh Academy.

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Bohr and The Atom

Niels Bohr’s Early Career

In March of 1912 Niels Bohr (1885–1962) arrived in Manchester to begin working with Rutherford. Previously, he had worked with Thomson in Cambridge. Unfortunately, their relationship had been strained from the start, and never really flourished as Bohr had hoped. Writing to his brother Harald, Bohr said:

“… Thomson has so far not been as easy to deal with as I thought the first day. …”

Perhaps, Bohr’s initial encounter with Thomson was to blame, where upon entering Thomson’s office, Bohr proclaimed:

“This is wrong.”

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Zero Point Energy

The zero point energy of a system is a direct consequence of the Heisenberg uncertainty principle.

Solid Helium

Although possible, helium does not easily solidify due to quantum effects related to its small atomic size.

When a Light Bulb Burns Out

A light bulb is more likely to burn out when first turned on since this is when the electrical resistance is the lowest. As the current flows it heats up the wire and the atoms begin to “jiggle”, which increases the electrical resistance.

Speed of Sound and Material Phase

The speed of sound depends on the phase of the material (solid, liquid, or gas). In general, sound travels fastest in solids, then liquids, then gases.

Matter in transition

Democritus saw material objects (matter) as existing in a temporary state, being created or destroyed as atoms respectively come together or fall apart under the influence of natural forces; all that remains then are the atoms comprising those material objects.

Atomos and Atoms

Democritus considers everything in the universe – including the human mind and soul, and even the gods – to be comprised of atomos, which is Greek for indivisible and from which we get “atom”.

Dalton and Atomic Weights

With a firm belief in atoms, impressive physical insight and armed with a few simple rules, Dalton was able to construct a table of relative weights, which he first presented in 1803 at a talk to the Literary and Philosophical Society of Manchester. In 1805, this effort first appeared in print, with a systematic explanation of the method appearing in 1808 when Dalton published the first volume of his book A New System of Chemical Philosophy. Here, with hydrogen as his reference, he gave the following relative weights: hydrogen (H) 1; nitrogen (N) 5; carbon (C) 5.4; oxygen (O) 7; phosphorus (P) 9; sulfur (S) 13 and so on, including several elements and compounds.

Cooling Soup

Cooling soup by blowing on a spoonful prior to placing it in your mouth works because the hotter atoms are literally blown away.  This is because the soup is made up of atoms comprised of a range of speeds. The atoms with the higher speeds – the hotter ones – are on top, hovering above the atoms with the lower speeds – the cooler ones. So, the end result of blowing on the spoonful of soup is that the hotter atoms are blown away, while the cooler ones are left behind.

Atomic Weight

The atomic weight of a mid-sized atom is around 0.00000000000000000000001 grams; a 1/400th of an inch grain of sand weighs about 0.001 grams.

Lavoisier on Constant Mass

In 1789, Lavoisier showed that the total mass during the course of a chemical reaction is unchanged. Rather the atoms simply “reorganize” themselves, kind of like the reshuffling of deck or cards.

Lavoisier’s 33 Elements

In 1789, Lavoisier published An Elementary Treatise on Chemistry where he describes 33 elements. The list begins with caloric and continues with light, oxygen, nitrogen and hydrogen.

Entropy and Atoms

Our understanding of the connection between entropy and the microscopic world of atoms is mostly due to the work of James Clerk Maxwell and Ludwig Boltzmann.

The Maxwell Distribution

Not all the atoms in a gas move at the same speed, but rather each atom takes on a speed lying in a specific range. For an ideal gas at equilibrium, this range is known as the Maxwell distribution. In 1860, Maxwell needed merely a single page to derive this amazing result, which also allowed him to calculate other important properties of a gas that matched with experimental observation.

Particles in Motion

That the properties of gases could be explained by particles in motion had been advocated in 1738 by Daniel Bernoulli (1700-1782), who proposed a model that is very similar to the one in acceptance today.

The First “Atomic Theories”

The first “atomic theories” focused on a “primary element” responsible for creating all other matter. Heraclitus said it was fire, Thales of Miletus (c.624 BC–c.546 BC) said it was water, Anaximenes (c.585 BC–c.528 BC) thought it was air, and Empedocles finally unified these declaring there to be the four elements of air, earth, fire and water. Later Aristotle adopted Empedocles’ four elements and so it remained up until about the 17th century.

Particle, Corpuscle, Element and Atom

Through the 18th century the words particle, corpuscle, element and atom were all used synonymously to refer to the building blocks of matter. In fact, no more insight into what an atom was had been accomplished since (the Greek philosopher) Democritus’ description some two thousand years prior.

Collisions in a Gas

The particles (atoms, molecules) of a gas move farther and faster (in a given interval of time) than those of a liquid. As they do so, a single particle undergoes about a billion collisions every second with other particles.

Atomic Energy States are Discrete

The energy states available to atoms and molecules occur at specific intervals. In other words, they are discrete rather than continuous.