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Daltons Atomic Theory - Model, Explanation, Drawbacks, FAQs

Daltons Atomic Theory - Model, Explanation, Drawbacks, FAQs

Team Careers360Updated on 02 Jul 2025, 04:47 PM IST

Explain Dalton’s Atomic Theory or John Dalton Atomic Theory

The theory which is based on the nature of matter (where matter is anything that has some mass or occupies space) discovered by an English Physicist and Chemist named John Dalton. Therefore also known as John Dalton’s atomic theory. John Dalton born in the year of 1766 and died at the age of 78 years i.e. in 1844. He is one of the English chemists who was born in a poor weaver’s family. He started his career as a school teacher and later became a school principal. He discovered the atomic theory of matter in 1808.

Dalton :

Picture of Dr. John Dalton

Matter is made up of indivisible particles known by the name atoms. According to Dalton’s atomic theory all substances are made up of small and indivisible particles called atoms. Atoms of elements are of same size and mass whereas different elements have also atoms of different sizes and masses. Compounds are generally formed by the combination of atoms which are present in constant and simple proportions.

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Dalton’s Atomic Model

The first structural, conceptual and arrangement of atoms were proposed by a model called Dalton’s atomic model. This model is given by the scientist John Dalton. Thus known as the John Dalton atomic model. This model is also known by the name modern atomic theory or atomic postulates. This model was discovered in 1803 and this was said to be the first atomic model.

Write the postulates of Dalton's atomic theory.

The main postulates of Dalton’s atomic model are given as follows:

1. The Dalton model is also known by some other name called spherical model. This name derived from the nature of the model as this model is made up of atoms which are indivisible and solid in nature and have the shape of a compact sphere.

2. This model is considered as the basic unit of all the matters.

3. Theory contains six main postulates.

4. Atoms of two or more elements interact with each other and form molecules.

5. This theory also suggested that matter is composed of very tiny particles known as atoms.

6. Same elements contain the same kind of atoms while different elements contain different types of elements.

7. The elements which contain different types of atoms have different weights from each other.

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Commonly Asked Questions

Q: What are the main postulates of Dalton's Atomic Theory?
A:
The main postulates are: 1) All matter is made of atoms, 2) Atoms of the same element are identical, 3) Atoms of different elements have different properties, 4) Atoms combine in whole number ratios to form compounds, and 5) Atoms cannot be created, destroyed, or divided in chemical reactions.
Q: How did Dalton's Atomic Theory explain chemical reactions?
A:
Dalton's theory explained chemical reactions as the rearrangement of atoms. It proposed that atoms combine, separate, or rearrange in chemical reactions, but are not created, destroyed, or changed into other types of atoms.
Q: How did Dalton represent atoms in his model?
A:
Dalton represented atoms as solid, indivisible spheres. He used different symbols for atoms of different elements, often circles with distinct markings or letters inside.
Q: What is the law of conservation of mass and how does it relate to Dalton's theory?
A:
The law of conservation of mass states that mass is neither created nor destroyed in chemical reactions. This aligns with Dalton's postulate that atoms are not created, destroyed, or changed in chemical reactions, only rearranged.
Q: What evidence supported Dalton's Atomic Theory?
A:
The theory was supported by the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. These laws were consistent with the idea of atoms combining in fixed ratios to form compounds.

State the postulates of Dalton’s atomic theory

There are six main postulates of Dalton’s atomic theory which can be described as follows:

1. First Postulate: As discussed in the Dalton atomic model, atoms are indivisible in nature and these are also indestructible and have homogeneous tiny sphere like shape. It is also known that elements are the combination of atoms and these types of particles will not show any change unless they undergo some chemical reaction.

2. Second postulate: Second postulate states that atoms of the same element are exactly similar to each other in weight as well as the other properties, different elements have different types of atoms.

3. Third postulate: Third postulate of Dalton’s atomic theory states that atoms are of indivisible nature i.e. it cannot be divided into further smaller particles as it is the smallest unit even in the presence of chemical reactions. Atoms are similar to conservation of mass like mass atoms are not created or destroyed. Complex compounds are the combination of atoms which will combine to form matter and atom is said to be the minimum unit for matter.

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4. Fourth postulate: This postulate describes the combination of atoms which further form compounds and atoms of different elements which combine with each other to always combine in whole ratio number.

5. Fifth postulate: This postulate states that atoms can also combine in different proportions which give rise to more than a single compound and this explanation also tells us about the number of atoms that exist in this universe.

6. Sixth postulate: Sixth postulate of Dalton's atomic theory states that combinations of two or more different or same atoms will form chemical compounds.

Dalton’s atomic model contribute with the following things:

1. In his first attempt Dalton was the one who was able to make us understand about the basic nature of matters.

2. It also gives us theoretical laws which are derived further.

3. This model helps us to understand the chemical nature of atomic masses of any compound or element.

4. This model also connects chemistry with a mathematical science which defines the combination of atoms which is in whole number.

5. It also gives us proper knowledge about the matter that it is made up of indivisible atoms and atoms further combine with each other to form compounds.

By explaining all these points Dalton also need some modifications in his theory and theory shows some drawbacks which are explained as:

Drawbacks of Dalton’s atomic theory

1. Subatomic particles: It does not provide any information about subatomic particles. As this theory suggested that atoms are indivisible in nature but with the discovery of subatomic particles like electrons, protons or neutrons will contradict this postulate as after this it is said that atom contains a nucleus in which proton and neutron are present and electrons are revolving around the nucleus.

2. Isotopes: This theory suggests that atoms of all elements have the same masses and densities. But different isotopes of the same element will have different masses so it contradicts the isotope point too.

3. Isobars: Dalton’s atomic theory tells that atoms of masses of two different elements are different from each other. But according to isobar definition two different elements may have the same mass number. Hence a contradiction arises between Dalton’s atomic theory and Isobar statement.

4. Whole number ratio: Theory says that elements should combine in whole numbers to form compounds but we can see a number of organic compounds which are not following this pattern so it contradicts their formation too.

5. Allotropes: Dalton’s atomic theory does not provide any information about allotropes of an element. Like diamond and graphite both are made up of similar elements called carbon but they have different properties that will not get explained by Dalton.

Other than drawbacks there are also some advantages or merits of Dalton’s atomic theory which can be explained as:

1. Many laws like law of conservation of mass, law of multiple proportion and law of constant proportion are not violated by Dalton’s law.

2. Theory well explained the difference between elements and compounds.

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NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

Q: How does Dalton's Atomic Theory relate to the concept of stoichiometric calculations?
A:
Dalton's theory, particularly the idea of atoms combining in fixed ratios, forms the basis of stoichiometric calculations. These calculations rely on the principle that the ratios of atoms in a reaction can be used to determine the quantities of reactants and products.
Q: How does Dalton's Atomic Theory relate to the law of constant composition?
A:
Dalton's theory explains the law of constant composition by proposing that compounds are formed by combining atoms in fixed, whole number ratios. This ensures that a given compound always has the same proportion of elements by mass.
Q: What is the relationship between Dalton's Atomic Theory and the concept of valency?
A:
While Dalton didn't directly address valency, his idea of atoms combining in fixed ratios laid the groundwork for the concept of valency, which describes the combining capacity of atoms in chemical reactions.
Q: What is the significance of Dalton's postulate that atoms cannot be subdivided in chemical reactions?
A:
This postulate established the atom as the fundamental unit of matter in chemical reactions. While we now know that atoms can be split in nuclear reactions, this idea remains true for chemical reactions, forming the basis of chemical stoichiometry.
Q: How does Dalton's Atomic Theory explain the concept of limiting reagents in chemical reactions?
A:
Dalton's theory, by proposing that atoms combine in fixed ratios, provides the basis for understanding limiting reagents. It explains why the amount of product formed is limited by the reactant present in the smallest stoichiometric quantity.
Q: What is the relationship between Dalton's Atomic Theory and the concept of empirical formulas?
A:
Dalton's theory, particularly the idea of atoms combining in simple whole number ratios, directly relates to the concept of empirical formulas, which represent the simplest whole number ratio of atoms in a compound.
Q: How did Dalton's Atomic Theory contribute to the understanding of chemical bonding?
A:
While Dalton didn't explicitly describe chemical bonding, his theory of atoms combining to form compounds laid the foundation for later theories of chemical bonding, including ionic and covalent bonds.
Q: What is the significance of Dalton's use of relative atomic weights?
A:
Dalton's use of relative atomic weights was crucial for comparing and quantifying different elements. It laid the groundwork for the modern atomic mass unit and the periodic table's arrangement of elements by atomic weight.
Q: How does Dalton's Atomic Theory relate to the concept of molecular mass?
A:
Dalton's theory, by proposing that compounds are formed from combinations of atoms, provides the basis for calculating molecular mass as the sum of the atomic masses of all atoms in a molecule.
Q: What is the relationship between Dalton's Atomic Theory and the concept of chemical equivalents?
A:
Dalton's theory of atoms combining in fixed ratios relates to the concept of chemical equivalents, which describes the mass of a substance that will react with or replace one mole of hydrogen atoms in a chemical reaction.
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