This was a real question by my 6yo. She asked what was made of atoms. I said everything, but they’re too small to see. “Oh, microscopic!” “Well, smaller actually.” “How do people know they exist? And what’s the name of the person who discovered them?”
Marked as chemistry cause that’s how ill-equipped I am to answer this question. Is it chemistry? Or should I have said physics?
In: 4
The development of atomic theory goes back to a few Greek philosophers who proposed the idea that there were limits to physical division; at some point you couldn’t keep dividing something, and it would be ‘atomos’, meaning indivisible.
This idea was largely seen as ridiculous and most people ignored it for about 2000 years.
In the early 1800s, John Dalton (like other chemists of the time) was experimenting with various chemicals, and noted that particular combinations would always have the exact same weight ratios in their reactions. He theorised that they were discrete combinations occurring at vast scale, and called the units of these atoms, after the old Greek idea.
Further proof for atomic theory came from Robert Brown, who noticed in the 1820’s that tiny particles in water would jiggle for no reason. It took until Einstein in 1905 for a formal explanation to arise – they moved because the water was actually made from tiny particles that were bouncing around.
In short, we considered the evidence available and eventually concluded that all of it could be explained by the existence of atoms.
These days, we can actually image individual atoms with the use of electron microscopes.
No single person discovered atoms. Historians characterize atomic theory as going through several distinct phases:
1. Philosophical atomism (ancient Greeks) — an approach that was the _idea_ of atoms as an abstract question about the world (basically one the answer to the question, “if you cut something in half, and then cut the remainder in half, and cut the remainder in half, would you eventually end up with something that couldn’t be cut?”) than any physical reality of them. It was edged out by Aristotle’s (non-atomic) theory of matter (plenism) for several thousand years.
2. Chemical atomism (18th/19th century product of the chemical revolution) — mainly attributed to Dalton, who basically said, “hey, this new approach to chemistry makes sense if you imagine each element is an atom and that these atoms can be combined into molecules. A lot of the people who practiced this did not know if atoms really existed or were just convenient abstractions.
3. Physical atomism (late 19th century through 20th century) — the creation of what we think of as the modern idea of atoms as collections of subatomic particles with a real physical structure. The discovery the electron (Thompson, 1897) as the first subatomic particle (Thompson believed it was the _only_ one) was used to start new work and speculation about atomic structure that, over the course of several decades, led to the understanding we have today.
As for how people know they exist: there are lots of experiments whose results wouldn’t make sense if atoms didn’t exist. There was no single experiment to establish their existence; it gradually just became assumed that they existed, because it made far more sense to imagine they existed than the contrary.
They are too small to see with our eyes, but that doesn’t mean we can’t see them in other ways.
When we take pictures we usually rely on photons, on visible light. Visible light has wavelengths between 380 to about 750 nanometers (there are 1 billion nanometers in one meter, or 25.4 million nm in one inch.). This works because most objects we take photographs of, such as plants or animals or people, are much much MUCH bigger than 380-750 nanometers.
But atoms are just too small, ranging in size from 50 picometers for one helium atom to 520 picometers across for one cesium atom. A picometer is 1 trillionth of one meter, meaning its 1000 times smaller than a nanometer. You could fit 730 cesium atoms in a row in the same length is the SHORTEST visible wavelength of light.
What that means is visible light never/almost never reflects off atoms. It would be like trying to detect if there was a grain of sand by bouncing a basketball off it. The odds that you’d hit the sand with the basketball are pretty tiny!
So if we want to take a “picture” of an atom we have to use something smaller than the atom. Fortunately we have something that we can use for that, electrons. Electrons are much smaller than atoms (though their exact size is up for debate), the range is between 10^(−18) and 10^(−22) meters. For comparison, the smallest atom (helium) is about 5*10^(-11) meters, meaning its 10 million to 100 billion times bigger than an electron. By using precisely controlled streams of electrons along with electron detection devices we can detect atoms and use the measurements we make to render images of them that we can then see.
Meanwhile electrons can be detected and controlled using magnetic fields because all electrons have a negative charge. So even if we can’t “see” them we can know there are there. Kind of like how you can know someone is in the room by smell or sound even if its pitch black and you can’t see them with your eyes.
No single person discovered atoms. Historians characterize atomic theory as going through several distinct phases:
1. Philosophical atomism (ancient Greeks) — an approach that was the _idea_ of atoms as an abstract question about the world (basically one the answer to the question, “if you cut something in half, and then cut the remainder in half, and cut the remainder in half, would you eventually end up with something that couldn’t be cut?”) than any physical reality of them. It was edged out by Aristotle’s (non-atomic) theory of matter (plenism) for several thousand years.
2. Chemical atomism (18th/19th century product of the chemical revolution) — mainly attributed to Dalton, who basically said, “hey, this new approach to chemistry makes sense if you imagine each element is an atom and that these atoms can be combined into molecules. A lot of the people who practiced this did not know if atoms really existed or were just convenient abstractions.
3. Physical atomism (late 19th century through 20th century) — the creation of what we think of as the modern idea of atoms as collections of subatomic particles with a real physical structure. The discovery the electron (Thompson, 1897) as the first subatomic particle (Thompson believed it was the _only_ one) was used to start new work and speculation about atomic structure that, over the course of several decades, led to the understanding we have today.
As for how people know they exist: there are lots of experiments whose results wouldn’t make sense if atoms didn’t exist. There was no single experiment to establish their existence; it gradually just became assumed that they existed, because it made far more sense to imagine they existed than the contrary.
They are too small to see with our eyes, but that doesn’t mean we can’t see them in other ways.
When we take pictures we usually rely on photons, on visible light. Visible light has wavelengths between 380 to about 750 nanometers (there are 1 billion nanometers in one meter, or 25.4 million nm in one inch.). This works because most objects we take photographs of, such as plants or animals or people, are much much MUCH bigger than 380-750 nanometers.
But atoms are just too small, ranging in size from 50 picometers for one helium atom to 520 picometers across for one cesium atom. A picometer is 1 trillionth of one meter, meaning its 1000 times smaller than a nanometer. You could fit 730 cesium atoms in a row in the same length is the SHORTEST visible wavelength of light.
What that means is visible light never/almost never reflects off atoms. It would be like trying to detect if there was a grain of sand by bouncing a basketball off it. The odds that you’d hit the sand with the basketball are pretty tiny!
So if we want to take a “picture” of an atom we have to use something smaller than the atom. Fortunately we have something that we can use for that, electrons. Electrons are much smaller than atoms (though their exact size is up for debate), the range is between 10^(−18) and 10^(−22) meters. For comparison, the smallest atom (helium) is about 5*10^(-11) meters, meaning its 10 million to 100 billion times bigger than an electron. By using precisely controlled streams of electrons along with electron detection devices we can detect atoms and use the measurements we make to render images of them that we can then see.
Meanwhile electrons can be detected and controlled using magnetic fields because all electrons have a negative charge. So even if we can’t “see” them we can know there are there. Kind of like how you can know someone is in the room by smell or sound even if its pitch black and you can’t see them with your eyes.
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