Chemistry · Structure Of Atom · NEET
It could not explain the Law of Gaseous Volumes (Gay-Lussac's law). Dalton's theory successfully explained the law of conservation of mass, the law of constant (definite) proportion, and the law of multiple proportion. But the whole-number volume ratios in which gases react were only explained later by Avogadro's hypothesis. This exact point was tested in NEET 2025.
Four simple points: (1) All matter is made of tiny indivisible particles called atoms. (2) Atoms of the same element are identical in mass and properties; atoms of different elements are different. (3) Atoms combine in simple whole-number ratios to form compounds. (4) Atoms are neither created nor destroyed in a chemical reaction — they only rearrange. Point 4 is why mass is conserved.
Dalton said all atoms of one element have the exact same mass. But isotopes are atoms of the same element with DIFFERENT masses (like Carbon-12 and Carbon-14). Since they have the same element but different masses, Dalton's rule 'atoms of an element are identical in mass' is broken. So his theory could not explain isotopes.
No. Dalton said the atom is the smallest indivisible particle. Later experiments discovered electrons, protons and neutrons INSIDE the atom. So the atom CAN be divided into subatomic particles. This is a major limitation and it is why the next chapter topic is the discovery of these particles.
Law of definite (constant) proportion: a given compound always has the same elements in the same fixed mass ratio (water is always 1:8 H:O by mass). Law of multiple proportion: when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a small whole-number ratio (CO vs CO2). Dalton's theory explains BOTH of these.
Dalton's atomic theory could not explain which of the following?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
John Dalton published his atomic theory in 1808 in 'A New System of Chemical Philosophy'. He had proposed the law of multiple proportion earlier, in 1803.
Partly. The idea that matter is made of atoms and that atoms combine in whole-number ratios is still correct and useful. But the parts saying atoms are indivisible and that all atoms of an element are identical in mass are now known to be wrong (subatomic particles and isotopes).
Remember four: (1) atoms are divisible (electrons, protons, neutrons exist), (2) isotopes have different masses for the same element, (3) isobars have same mass for different elements, and (4) it cannot explain the law of gaseous volumes. The gaseous-volumes point is the most commonly asked.
Three laws: law of conservation of mass, law of constant (definite) proportion, and law of multiple proportion. These three are the 'safe' options — Dalton CAN explain them, so they are the wrong choices when a question asks what he could not explain.
