Dalton’s atomic theory

Dalton’s atomic theory is a theory on the nature of matter which states that all matter is composed of small, indivisible particles called “atoms”. The theory was put forth by renowned English physicist and chemist, John Dalton in 1808. According to John Dalton, “All substances are made up of atoms that are indivisible and indestructible building units”. He further proposed that all the compounds were a combination of these atoms in defined ratios. Dalton also hypothesized that chemical reactions resulted in the rearrangement of the reacting atoms. The postulates and limitations of Dalton’s atomic theory are given below:

The foundation of Dalton’s theory

Dalton established his theory on the basis of rudimentary laws of chemistry, namely, the “law of conservation of mass” and the “law of constant composition”. According to the law of conservation of mass, matter cannot be created or destroyed in a closed system. This means the initial materials and the finished product of a chemical reaction must be composed of the same amount of each element. Every time we balance the equations, we apply the principle of conservation of mass. As for the law of constant composition, the proportions of elements in a compound remain the same no matter how the compound is formed. It is also known as the “law of constant proportions” or “definite proportions”. For instance, in salt, the molecular formula (NaCl) contains the same proportion of sodium and chlorine no matter its quantity or origin. On the basis of these two laws, Dalton formed his Atomic Model Theory. The main postulates of Dalton’s atomic theory are:

All matter is made of tiny, individual particles called “atoms”

Dalton proposed that all matters consist of small, indivisible particles called “atoms”. He further proposed that these atoms cannot be destroyed or altered by chemical means but can be combined with other elements to form complex structures.

• The mass and properties of all atoms of a given element are the same

Dalton proposed that every atom of a given element is the same as the other atom of a similar element. For example, an atom of the element Sodium (Na) has mass equal to the mass of all other atoms of Sodium. This also means that all the atoms of an element share the same set of properties such as boiling point, freezing point, etc.

Atoms of an element can be combined with other elements to form a new compound.

Dalton proposed that a compound is created when there is a reaction between two different atoms. An example of such a compound would be common salt. Salt is a combination of separate elements, Sodium (Na) and Chlorine (Cl).

• During a chemical reaction, atoms rearrange themselves

In the final part of Dalton’s atomic theory, he postulated that in a chemical reaction, atoms are neither destroyed nor created, they merely rearrange themselves to form a new compound. Let’s use the example of NaCl once again. When sodium combines with chlorine to form salt, the sodium and chlorine atoms remain. However, these atoms simply rearrange themselves to form a new compound which is salt.

Limitations of Dalton’s atomic theory

Even though Dalton’s atomic theory formed the framework of modern chemistry, a lot of limitations in the theory have resurfaced ever since. We’ve learned many facts as we progressed from the first model of atomic theory to realise a few loopholes. Here are a few of those: – Atoms are further divisible After the discovery of subatomic particles, we now know that atoms are further divisible. Which is a contradiction to Dalton’s belief. In conclusion, atoms are not indivisible because they can be further divided into electrons, neutrons, and protons. – It didn’t account for isotopes and isobars After a few spectrometry experiments, it demonstrated that atoms of the same elements of the same compounds can have different masses. Dalton’s theory had to be modified after this discovery that different isotopes of elements can have different masses. -It failed to account for allotropes The fact that elements such as diamond and graphite have the same element, carbon, but different properties, couldn’t be explained by Dalton’s model.

Conclusion

Despite the multiple limitations of Dalton’s atomic theory, its basic model still holds its value and significance. To date, Dalton’s theory exists as the framework of the ones that followed it. What Dalton achieved in the field of chemistry is something that can arguably be not emulated. As suggested by John Dalton, everything that we see around us is indeed made up of atoms. Check out the key points of the atomic theory model suggested by Dalton: – Dalton pioneered the description that all matter existed in terms of atoms and their properties. It was the first of its kind within the world of his atomic theories. – Dalton’s theory is based on the law of conservation of mass and the law of constant composition. – According to his theory, all matter is made up of indivisible and indestructible atoms. – In the second part of the theory, he suggested that each atom within a given element has the same mass and properties. – According to the third part, compounds are made up of two or more types of atoms. – The fourth part of his theory suggests that a chemical reaction is a rearrangement of atoms. – After the discovery of isotopes and isobars, the atomic model theory was revised.