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John Dalton's Atomic Theory

Last time we learned that during ancient times, in Greece and India, people came up with concepts that would later form the underlying basis of atomic theory. We later learned that for the next few hundred years (over 1000 actually but who's counting) nobody touched atomic theory.

So what changed? New theories and laws of nature came about that caused one John Dalton (no, not the Kinks' bassist, the other John Dalton) to wake up and come up with his own atomic theory.

The basis to Dalton's theory

There are a few important rules that came about in the late 1700s that were crucial to Dalton's thoughts. First was the Law of Conservation of mass. This law, formulated by Lavoisier, states that during a chemical reaction, the total mass of the reactants equals the total mass of the products. This suggested that matter is indestructible.

The second law was called the Law of Definite Proportions proposed by Proust. The law states that whatever quantity of a substance you take, the proportions of the masses of elements composing this substance will always remain equal. For example, The ratio of Oxygen to Carbon in a tiny vile of carbon dioxide will equal the ratio of O to C in a large container. Dalton expanded upon this law in formulating his own Law of Multiple Proportions, which states that elements combine in whole-number ratios to form compounds, never in fractions or unwhole numbers.

Dalton was trying to explain why water absorbs different gases in different proportions. He decided that an atomic theory can provide an explanation.

The theory:

Here are the main points of Dalton's atomic theory:

• All elements are made of tiny tiny particles, called atoms.
• All atoms of one element are identical, though atoms of different elements are different, specifically in terms of mass.
• Atoms of one element combine with atoms of another element to form compounds. The molecules of these compounds always have the same proportions of elemental atoms.
• Atoms can't be created, destroyed, or subdivided.

It's worth noting that this theory isn't totally accepted today- lots of improvements were made over the years. For example, we now know that atoms can be subdivided into protons, electrons, and neutrons. We'll get to that later though.

Another point Dalton raised wasn't accepted at the time, and rightfully so. Dalton supported the "greatest simplicity law", which proposed that elements in 1:1 ratios, i.e. water should have the formula HO, which we know is false. Dalton also imagined that in nature atoms always come in single groups, which we know is false too- most gases, like hydrogen and oxygen, are diatomic and are found in nature as a molecule of 2 atoms.

Based on his ideas, Dalton published a chart of atomic weights, using Hydrogen as the base weight of 1 unit and the other elements (oxygen, carbon, nitrogen, sulphur and phosphorus) as in proportions. Of course, not knowing the diatomic concept and his simplifying misconception caused him to be way off.

And then what happened?

Dalton's atomic theory can be thought of as the theory of tiny spheres:

Once this theory was introduced, things started to move a lot more rapidly. Everyone seemed to be researching this or that, trying to find out something worthy and get into the history (and science) books.

Some of them did. Dalton's model didn't survive long, and it was quickly replaced by a chocolate chip cookie…

To be continued in Part-3