John Dalton’s atomic theory experiment was the first attempt to describe all matter by way of atoms and their properties in a way that was complete. His theory was based on two verified scientific laws: the law of conservation of mass and the law of constant composition.
The law of conservation of mass says that within a closed system, no matter can be created or destroyed. This means if a chemical reaction happens to create something new, then the amount of each element must come from the same starting materials. It is for this reason that mathematics seeks to create equality and balance.
The law of constant composition says that pure compounds will always have the same proportion of the same elements. That means if you were to look at salt crystals, then you would have the same proportions of the base elements, chlorine and salt, no matter how much salt you had or where you got the salt. Now other items could be added to the salt to change it, but the core atoms of salt are always the same.
The Four Principles of Dalton’s Atomic Theory
When Dalton proposed his atomic theory, it was based on ideas, assumptions, and principles more than facts that were directly observable. This means that there are five components to the atomic theory that are offered by Dalton.
- All matter is made up of atoms. This means that everything that is made of matter is composed of atoms, which are indivisible by design.
- All atoms can be identified by mass and properties. This means that any given element has atoms that must be identical in properties, including their mass. It also means that an element can be identified because its atoms will act like a fingerprint to identify it.
- All compounds are made up of atom combinations. For a compound to form, Dalton suggested with his atomic theory that it would have to be composed of at least two different types of atoms. A combination may also include more than two.
- All chemical reactions are a rearrangement of atoms. This indicates that when a chemical reaction occurs, it is because the atoms are being rearranged in such a way that they form a different combination. It is a whole-number ratio.
- If an element reacts, their atoms may sometimes combine into more than one simple whole-number ratio. This would help to explain why weight ratios in various gases were simple multiples of each other.
Dalton had another postulate that he included with his initial atomic theory that, unfortunately, made it difficult for the scientific community to accept his ideas in their entirety. He believed that when atoms combined in only one ratio, then it needed to be assumed that it would be a binary ratio. This caused him to believe that the formula for water was HO instead of H2O and ammonia was NH instead of NH3.
Dalton had made the same mistake that many had before. Based on his own work, he made an assumption that turned out to not be true. This is why experimentation is so critical to the scientific process.
The Atomic Theory, Experimentations, and Its Modern View
When we look at an atomic theory experiment, what we’re trying to do is either prove that Dalton’s theory is correct or prove that it is incorrect. Evidence must be obtained in order for this to occur, which can only be done through experimentation and observation. Since the theory was first proposed, we have learned quite a lot about atoms and can prove that components of Dalton’s theory are categorically incorrect.
For example: in Principle #1, Dalton stated that atoms were indivisible by design. We know that this is not the case. Atoms are actually made of positive components called protons, negative components called electrons, and neutral components that are called neutrons. Instead of being units that are made up of great mass, atomic theory experiments were able to prove that a vast majority of atoms are basically just empty space.
There are more experiments that have helped to disprove other elements of Dalton’s atomic theory as well, though it would take several generations for scientists to realize that there was a greater truth to find.
The Issue of Neutrons and Isotopes with the Atomic Theory
In Principle #2 of Dalton’s atomic theory, we have found that the idea of atoms having the same mass within a specific element is also incorrect. This is because the number of neutrons that may be present within an atom can vary based on the different isotopes which exist for the same element.
This means Dalton was partially correct, but also partially incorrect. Here’s why.
Let’s take carbon as an example. At the time of this writing, there are 15 known types of carbon that currently exist. Some are natural, while others are artificial. The most stable carbon isotope has a half-life of 5,700 years, while the most stable artificial carbon isotope has a half-life of just 20 minutes. There are actually 3 different occurring isotopes of carbon that occur in nature.
Each isotope is assigned a number. Using the naturally occurring isotopes as an example, they are Carbon-12, Carbon-13, and Carbon-14. These numbers are assigned in such a way not because of the order in which they were discovered, but because each one has a specific isotopic mass.
This means Carbon-8 has an isotopic mass that is close to 8u exactly. Carbon-12 would be 12u. And so forth.
So what the atomic theory experiments regarding atomic number, mass number, and isotopes has been able to determine is this: elements can have different masses. The specific isotopes, however, do not have a different mass. So Dalton was partially correct because you’re not going to find Carbon-14 atoms when you’re looking at Carbon-12. He was partially incorrect because at the time, it was not known that elements could have these different isotope masses.
Dalton’s Atomic Theory and It’s One Missing Item
Maybe you’ve heard of a Quark. No – not the Ferengi bartender on the show Star Trek: Deep Space Nine. Quarks are subatomic particles that carry a fractional electrical charge. They have not been directly observed, but their existence has been predicted and confirmed through experimentation. It is considered to be an elementary particle.
Quarks are considered to be the very building blocks of each atom. They are a primary constituent of neutrons and protons, which means they are part of all ordinary matter. We can determine if an atom will be composing a proton or a neutron because of the number of “up” and “down” quarks that are found.
Two up quarks with one down quark make up a proton. Two down quarks with one up quark make up a neutron.
But these aren’t the only quarks that have been found since Dalton first proposed the atomic theory. Here are some of the other quarks that have been determined to exist.
- Strange Quark. Discovered with the lambda particle, the quark was deemed to be strange because it gave the nucleus of the particle a longer half-life than expected. A lambda particle is a different baryon formation than what creates protons and neutrons. The lambda consists of one up quark, one down quark, and one strange quark.
- Charm Quark. This quark was discovered through experimentation in 1974 and can be transformed into a charm quark.
- Top Quark. Evidence of a third quark was reported in 1995, found through the collision of protons and antiprotons in a collider. Little is known about this quark, other than its mass is quite large compared to other quarks that are believed to exist.
When Dalton was conducting atomic theory experiments, he conducted meteorology experiments because he wanted to prove that evaporated water could exist in the atmosphere as an independent gas. Instead of water molecules and air molecules mixing together, what would happen if it could be proven that they were actually separated?
This caused him to perform experiments on a series of gas mixtures to determine what effect each individual gas may have on the other. Through his observations, he was able to come up with what would become the first version of the atomic theory. It is a process that is still being evaluated to this day.
What Does Dalton’s Atomic Theory Mean Today?
When Dalton first proposed his atomic theory, there was no way to even predict the existence of protons, electrons, and neutrons – much less the existence of quarks or other subatomic particles. Yet when one looks at the entirety of the theory that was offered, many components of it are still considered to be true. It even provides much of the framework that is used in modern chemistry efforts.
Through experimentation, parts of the theory have been modified because of new knowledge. The principles, however, have offered multiple generations of scientists and researchers to know more about the smallest components of our universe. With future experimentation, we can continue to use Dalton’s atomic theory as a foundation for new discoveries.