Ever since the ancient times, scientific community has been so curious to know the nature and structure of the smallest particle called atom. Let it be ancient Democritus or modern Bohr, everyone was so dedicated to uncover the true and exact reality of atom. In this article, I’m going to provide explanation of Dalton’s atomic theory.
Really, considering the importance of basic building block of matter, understanding all the essential theories of atom in detailed manner is unavoidable. First of all, let’s begin with explanation of Dalton’s atomic theory.
Meaning and definition of atom
Atom is a smallest particle of matter. It displays the properties of chemical elements it belong. Actually, its definition enriched over a period of time with the development of different theories.
Dalton, Thompson, Rutherford, and Bhor enriched the understanding of atom by the means of theirs successive theories.
In order to understand the totality of atom, it is utmost important to present a detailed explanation of theories of atom evolved since ancient times.
Theory and hypothesis difference
Before to proceed to understand the theories of atom, it is necessary to know the meaning of theory and hypothesis.
In scientific terms, theory means a well proved explanation with genuine supporting reasons and can be used to predict something in question.
For layman’s understanding, theory is a logical explanation on the basis of facts and evidences. Why does it rain? Why does wind blows in the way it does? etc.
Unlike hypothesis, theory is used to generalize phenomenon.
On the other hand, hypothesis is a possible explanation based on observation, and it is yet to be tested. Simply put, hypothesis is a simple guess of things happening as part of observation.
In this article, “Explanation of theories of atom” I’m going to explain in simple way the various theories and hypothesis presented by renowned scientists.
Overview of Ancient atomic theory
Before to begin to learn the Dalton’s atomic model, it is essential to give due respect to the ancient scientists who theorized some important knowledge regarding atom.
In ancient period, Leucippus and Democritus, in the fifth century B.C. were believed that, “All the matter is made up of tiny units called atoms”.
In addition, they proposed that atoms are solid particles with variety of shapes and size. As per theirs belief, if the atoms are solid, then, it is impossible to have internal structure.
In the language of ancient Greeks, “atom is indivisible” –Democritus Now, let’s see the Dalton’s atomic theory.
Understanding detailed explanation of Dalton’s atomic theory
John Dalton was english physicist and chemist. He came up with his idea based on the ancient Greek notion that atom is indivisible. In 1808, he proposed his atomic theory.
Basis for Dalton’s theory
Dalton proposed his atomic theory on the basis of following laws and notions.
The laws of chemical combinations given by Lovoisier and Joseph L. Proust were the basis for formulation of dalton’s atomic theory.
The two laws, the law of conservation of mass and second the law of constant proportions were the basis on which Dalton formulated theory and uphold the ideas of earlier philosophers as well as scientists.
Important Postulates of Dalton
Look at the following postulates given by John Dalton.
- Matter is made up of tiny indivisible particles called atoms — Greek belief.
- Atoms of same elements are identical in shape, size, mass. And, atoms of different elements are different in mass, size, and other properties.
- Atoms can neither be created nor be destroyed — the law of conservation of mass.
- Atoms of different elements are combined with each other in fixed whole-number ratios in order to form compounds– the law of constant composition.
- Finally, atoms can be rearranged, combined, or separated in chemical reactions.
These are the postulates of Dalton’s atomic theory he proposed in 1808. Hereon, I’m going to point out the merits and limitations of the Dalton’s atomic model.
Merits of Dalton’s atomic model
Undoubtedly, Dalton’s atomic theory was the first that addressed the basic building block of atom in detailed manner.
It laid the theoretical foundation for the further research of atom, and it has been followed by other scientists.
Dalton’s atomic theory well differentiated between elements and compounds first time.
His theory upholded the law of chemical combinations, law of conservation of matter, and the law of constant proportion.
Bottlenecks or limitations of Dalton’s atomic theory
Though the Dalton’s atomic theory was first modern theory of atom, it was not free from limitations due to lack of sufficient knowledge base and technological bottlenecks in the research. Following are some limitations of Dalton’s atomic theory.
Atom is indivisible
Basically, Dalton’s atomic model was based on ancient Greek notion that atom is indivisible. If the atom is indivisible, it is impossible to have internal structure of atom. In other words, Dalton did not state about the subatomic particles that later discovered.
He didn’t explain isotopes and isobars
His assumption that different atoms of elements are identical in masses and densities. Actually, different isotopes of elements have different atomic masses-carbon has two isotopes with mass numbers 12 and 14.
And, he further stated that masses of different atoms of different elements are different. But, it possible to have same mass number for different atoms of different elements.
These are some notable limitations that Dalton’s atomic theory failed to explain. Later, Thompson, Rutherford and Bhor enriched the understanding of atom by theirs theories. Plum pudding model of Thompson first discovered negatively charged particles from cathode ray tubes experiments.
Last words on explanation of Dalton’s atomic theory,
So far I have explained how understanding of atom began in ancient times and evolved in modern world.
Though the notion of atom in ancient times was somehow true, but it was the John Dalton who proposed first scientific theory on the basis of three laws — law of chemical combinations, law of conservation of matter and law of constant proportion.
Due to lack of adequate technology and knowledge base, Dalton didn’t success in providing comprehensive theory of atom.
However, given the circumstances, it was the stepping stone in search of atom. And, later it was proved by later scientists like Thompson, Rutherford and Bhor.
Now, let’s take a look at the short summary of explanation of Dalton’s atomic theory for in-depth understanding and quick recall.
Short summary of explanation Dalton’s atomic theory
- Way before John Dalton, it was Democritus in the fifth century BC, who believes that “All the matter is made up of tiny units called atoms”. He further stated that atom is indivisible.
- Later, english physicist and chemist, John Dalton upheld the ancient Greek notion and proposed his atomic theory.
- His theory was based on the law of chemical combinations, law of conservation of matter, and law of constant proportion.
- He successfully differentiated between elements and compounds. But, failed to explain isotopes, isobars, internal structure of atom and allotropes.
- In his first postulate, he stated that matter is made up of tiny particles called atoms. His atom was indivisible.
- In his second postulate, he added that atoms of same element are identical in masses, density and properties.
- Later, he stated that compound is formed by two or more atoms of different elements.
- And, finally, he stated that chemical reaction is the rearrangement of atoms.
- Despite all the drawbacks, his theory laid the foundation for the scientific community to study matter in the form of atoms and theirs properties.
- These are key points of explanation of Dalton’s atomic theory. Now, let’s see the solved questions on explanation of Dalton’s atomic theory.
Solved questions on explanation of Dalton’s atomic theory
Take a careful look at the following solved questions. It will help you to grasp quickly subject matter and essence of this article.
Q. 1. Who was John Dalton?
Ans: John Dalton was english physicist and chemist who in 1808 proposed atomic theory.
Q. 2. Who was Democritus?
Ans: Democritus was ancient Greek who developed ideas of atom first. He believed that “the matter is made up of tiny units called atoms” and, atom is indivisible.
Q. 3. What is difference between theory and hypothesis?
Ans: Theory is a proved explanation of given observation in the light of facts and evidences. While, hypothesis is an untested guess about something.
Q. 4. What were the basis of Dalton’s atomic theory?
Ans: Law of chemical combinations, law of conservation of matter, and law of constant proportion were the basis of his atomic theory.
Q. 5. What are the postulates of Dalton’s atomic theory?
Ans: First, matter is made up of tiny particles called atoms. His atom was indivisible. Second, atoms of same element are identical in masses, density and properties.
Third, compound is formed by two or more atoms of different elements. Fourth, chemical reaction is the rearrangement of atoms.
Q. 6. Why does Dalton’s atomic theory value by scientific community?
Ans: It was first attempt to explain the matter in terms of atoms and theirs properties. Second, it laid the foundation for the further research. Third, it successfully upheld the laws of chemical combinations, conservation of matter, and constant proportion. Fourth, despite lack of adequate technology and knowledge base, it was praiseworthy attempt deserves respect.
Note : this article Explanation of Dalton’s atomic theory is strictly based on NCERT textbooks.
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