The modern atomic theory proposing that matter is made up of tiny indivisible atoms arranged in definite proportions was first systematically devised by which scientist?

Introduction / Context:

This question checks your understanding of the historical development of atomic theory in chemistry and physics. The idea that matter is composed of tiny indivisible units called atoms is central to modern science, but it was not always clearly formulated. Recognising which scientist first proposed a systematic atomic theory with clear postulates is an important basic fact in both chemistry and general science for competitive exams.

Given Data / Assumptions:

• The subject is the original modern atomic theory in chemistry, not later quantum models.
• The theory described matter as composed of small indivisible atoms that combine in fixed ratios.
• The options list several famous physicists and chemists involved in atomic research.
• The question is asking for the earliest systematic formulation of atomic theory in the modern scientific era.

Concept / Approach:

John Dalton, an English chemist and physicist, is credited with formulating the first modern atomic theory in the early nineteenth century. Dalton proposed that elements are made up of indivisible atoms, that atoms of the same element are identical, and that compounds are formed when atoms of different elements combine in fixed simple ratios. Later scientists such as J. J. Thomson, Ernest Rutherford and Niels Bohr refined the internal structure of the atom, but they built upon Dalton s basic concept that matter consists of atoms.

Step-by-Step Solution:

Verification / Alternative check:

Chemistry textbooks routinely start the atomic theory chapter with Dalton s postulates. Historical discussions also describe him as the father of modern atomic theory. Later sections cover Thomson s discovery of the electron, Rutherford s gold foil experiment and Bohr s quantum model, all of which refine Dalton s idea but do not replace his role as the originator of the atomic concept in modern form.

Why Other Options Are Wrong:

Niels Bohr introduced a quantum model of the hydrogen atom with electrons in quantised orbits, which is a later development, not the original atomic theory itself.

J. J. Thomson discovered the electron and proposed the plum pudding model; he did not first devise the idea that matter is made up of atoms.

Ernest Rutherford discovered the nucleus and proposed a nuclear model showing that atoms have a small dense center, but this again builds on Dalton s earlier concept.

Henry Moseley contributed to the understanding of atomic number and X ray spectra, confirming the ordering of elements, but he did not originate the basic atomic theory.

Common Pitfalls:

Students sometimes confuse the origin of the atomic concept with the discovery of the electron or nucleus. Because later scientists are more closely associated with the structure of atoms, it is easy to forget that Dalton worked before them and gave the first consistent atomic theory. To avoid this, remember the timeline Dalton, then Thomson, Rutherford and Bohr in sequence.

Final Answer:

The modern atomic theory was first systematically devised by John Dalton.