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But why would Dalton, one of the world's leading chemists, begin to think that Aristotle's theory was wrong, when everybody had believed it for over two millennia? And why, of all people, would Dalton begin to agree with Democritus, the laughing stock of ancient Greece?
Well, originally, Dalton, just like everybody else, believed in Aristotle's theory of water, earth, air, and fire. But around Dalton's time, the scientific community began to believe that a theory should be backed up by experiments, data, reason and logic. But Aristotle theory was not based off of any experiments, and it had no data to back it up! Aristotle simply looked out into the world and saw four great "elements" of nature.
So Dalton was on a mission to devise several experiments to prove that Aristotle was right, backed up by unarguable data. But when Dalton performed experiment after experiment, he found that Aristotle's theory simply could not explain what was happening in his experiments. So Dalton was forced to conclude that perhaps Aristotle was wrong, and that he needed to come up with a new theory.
To Dalton's surprise, his own theory was rather similar to that proposed by Democritus two thousand years ago. But Dalton did notice that their theories were NOT the same; there were a few key differences to pay attention to. Eventually Dalton published his findings to the world, which consisted of six main parts:
1) All elements are made of extremely tiny parts called atoms.
2) Atoms are the smallest units in the world; they cannot be broken down into smaller parts
3) Atoms from the same element have the same size, weight, and properties.
4) Atoms from different elements have different sizes, weights, and properties.
5) Atoms can be combined, separated, and rearranged in whole number ratios
6) Atoms from different elements can combine in repeating units to form different compounds
That's a lot to digest. Let's break Dalton's theory down and see what he's really saying.
At first glance, Dalton's theory seems to be very similar to Democritus'. Like Democritus, Dalton believed that the world is NOT made of water, earth, air, and fire; instead they both claimed that tiny little units make up everything in the world. Democritus called these tiny units atomos, and Dalton called them atoms (Dalton took inspiration for the name from Democritus' theory). Both Dalton and Democritus also claimed that these tiny little units (a.k.a. atoms / atomos) were the smallest things in the universe; they said that there was nothing smaller than them.
Dalton and Democritus also agreed that there was more than one type of atom (or atomos), BUT they disagreed on what the different types of atoms are.
Democritus said that each substance (or element) has its own type of atom. For example, logs have wood atoms, rabbits have fur atoms, salt has salt atoms, and so on. There are thousands of different objects in the world, so Democritus believed that there were thousands of different types of atoms.
Dalton said that there were only a few number (about a hundred) of elements in the world. Each element has its own type of atoms, and when these atoms are put together in repeating units, they can form a compound.
For example, sodium, chlorine, carbon, and hydrogen are four of about a hundred elements. When sodium and chlorine atoms are put together, a compound (salt) is formed. When carbon and hydrogen atoms are put together, a different compound (methane) is formed. Dalton predicted that all substances in our world are made this way.
And here Dalton was right; there are only a few types of elements that make up everything in our world. And what's even more impressive is that Dalton properly determined that there are only a finite number of natural elements in the world, before we found and collected all of them in The Periodic Table!
Dalton's next key point was that atoms from the same elements are identical. In other words, one carbon atom will always be the same size as another carbon atom. And one oxygen atom will always weigh as much as another oxygen atom. But a carbon atom will NOT be the same size as an oxygen one.
But where Dalton began to go wrong came from his hypothesis that atoms will always try to bond in a 1:1 ratio unless that compounds already exists. In simpler terms, Dalton thought that if a compound is made of sodium (Na) and chlorine (Cl), it must be NaCl.
In this case, Dalton would be right. Common table salt, or sodium chloride, is made up of sodium and chlorine, and does have the chemical formula of NaCl. But Dalton thought that all compounds had this ratio; that is, Dalton thought water (H2O) was HO, methane (CH4) was CH, and so on. If a ratio was already taken up (Carbon monoxide = CO), the next compound to be discovered would add another element (Carbon dioxide = CO2). So even though Dalton was luckily right sometimes, he didn't really understand what was going on in atoms and why water has to be H2O and not HO (we'll get to that later). Dalton's theory also had several other flaws (like Aristotle's and Democritus), but this theory was still a HUGE step forward after 2,000 years of no progress.
Once Dalton published his findings with data and simple, repeatable experiments, the entire scientific community realized that Aristotle's theory was wrong. Still, many were not convinced that Dalton was 100% correct; after all, he couldn't even really explain why water had to be HO and methane had to be CH.
The search for the structure of the atom was afoot! And the next puzzle piece would be, surprisingly, found by one of Dalton's students.
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