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.
The photoelectric effect is a result of electron-photon pair collisions.
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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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.
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.
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.”
The atom concept has its origins in Ancient Greek debates over the nature of change and permanency.
The zero point energy of a system is a direct consequence of the Heisenberg uncertainty principle.
A major stumbling block to Dalton’s success was his poor experimental technique.
Although it has no overall charge, a neutron still has a magnetic moment.
Although possible, helium does not easily solidify due to quantum effects related to its small atomic size.
The probabilistic interpretation of quantum mechanics is due to Max Born.
Unlike the crystal an amorphous solid or glass is a disorder arrangement of the atoms of the condensed phase.
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.
In gases like air, sound travels via collisions with the molecules; sound travels faster in gases when the temperature is increased (and the density is held constant).
Sound travels faster in air as the temperature increases.
At the microscopic level entropy is intimately connected to the motion of atoms.
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.
The atomic theory of Dalton was fatally flawed by his belief that the same atoms couldn’t combine.
Temperature is a measure of the average translational kinetic energy a single molecule in a given system possesses.
Michael Faraday’s experiments in the 1830s provided an initial “peek” at the electrons inside the atom.
The atoms of a Bose-Einstein fluid are in the exact same quantum state.
Aristotle criticized Democritus‘ atomic theory, which both hindered its acceptance and provided the majority of what we know about it.
“Nothing exists except atoms and empty space; everything else is opinion.” –Democritus
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.
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”.
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.
Modern atomic theory began in 1808 when Dalton published A New System of Chemical Philosophy.
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.
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.
Proposed in 1811, Avogadro’s Hypothesis only began to gain acceptance in 1858 (two years after his death) thanks to Stanislao Cannizzaro.
Einstein‘s doctoral thesis was entitled: On A New Determination of Molecular Dimensions. Extensions of this effort lead to his famous paper on Brownian motion in 1905, which helped to solidified the existence of atoms.
In 1909, Jean Baptiste Perrin provided the first accurate experimental determination of Avogadro’s number.
Einstein predicted stimulated emission can occur when light and matter interact; this idea forms the basis of the modern laser.
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.
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.
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 Greek philosopher Anaxagoras considered matter to be infinitely divisible.
A long time proponent of atoms, Boltzmann died unaware of Einstein’s landmark 1905 paper, which proved their existence.
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.
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” 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.
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.
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.
At the atomic level, energy occurs as “chunks” or quanta.
Transitions between the energy states of atoms and molecules require a specific amount of energy, nothing more, nothing less; it’s only these particular values that are allowed by nature.
The energy states available to atoms and molecules occur at specific intervals. In other words, they are discrete rather than continuous.
