Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Dalton's Atomic Theory, proposed in 1808, states that all matter is composed of tiny, indivisible particles called atoms ().
Atoms of a given element are identical in mass and chemical properties, while atoms of different elements differ in mass and properties ().
Compounds are formed when atoms of different elements combine in a fixed, simple whole-number ratio, such as , , etc. (e.g., ).
Chemical reactions involve the reorganization of atoms; atoms are neither created nor destroyed in a chemical reaction, which explains the Law of Conservation of Mass.
The theory provides a theoretical justification for the Law of Definite Proportions and the Law of Multiple Proportions.
Limitations of the theory: It does not account for subatomic particles (, , ), isotopes (atoms of the same element with different masses like and ), or isobars.
📐Formulae
💡Examples
Problem 1:
Nitrogen and Oxygen combine to form various oxides like and . Which postulate of Dalton's Atomic Theory explains this observation?
Solution:
This is explained by the postulate stating that 'Atoms of different elements combine in simple whole-number ratios to form compounds.'
Explanation:
In , the ratio is , and in , the ratio is . Dalton's theory explains that because atoms are discrete units, they must combine in integer ratios, supporting the Law of Multiple Proportions.
Problem 2:
Explain why the discovery of isotopes like and posed a challenge to Dalton's Atomic Theory.
Solution:
Dalton's second postulate stated: 'Atoms of the same element are identical in all respects, including mass.'
Explanation:
The existence of isotopes ( and ) shows that atoms of the same element () can have different masses, which contradicts Dalton's original assumption of identical masses for all atoms of a specific element.