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What if ... The two laws discussed here formed the basis of Dalton’s Atomic Theory. This theory attempts to logically explain why substances combine atoms could in fixed proportions and why there is no loss or gain of mass during a combine in any ratio and not in a chemical reaction. Dalton later explained these by proposing that during a fixed ratio? How chemical reaction, atoms are indivisible and merely rearrange, rather than would this affect being created or destroyed. the substances around us? 9.3 Dalton’s Atomic Theory John Dalton proposed his atomic theory in terms of certain postulates. These postulates combined earlier experimental observations and served as the basis for modern scientific theory. A postulate is a fundamental assumption accepted as truth without formal proof from which further ideas are formed or developed. Meet a Scientist John Dalton postulated that: All matter is made up of very tiny particles called John Dalton y was born in atoms, which participate in chemical reactions. England. In 1793, y Atomsareindivisibleparticles,whichcannotbecreated Dalton moved or destroyed in a chemical reaction. to Manchester y Atoms of a given element are identical in mass and to teach chemical properties. mathematics, physics and Atoms of different elements have different masses and chemistry at a college. He spent y chemical properties. most of his life teaching and y Atoms combine in the ratio of simple whole numbers to researching there. In 1808, he form compounds. presented his atomic theory, y The relative number and kinds of atoms are constant in which proved to be a turning a given compound. point in the study of matter. Dalton’s postulates provide the basis for the modern understanding of atoms and their behaviour. For example, hydrogen and oxygen atoms combine to form water, but the atoms themselves are not destroyed or changed into something else. Similarly, when magnesium burns in air, a white powder of magnesium oxide forms. This shows that the atoms of magnesium have combined with those of oxygen to form magnesium oxide. Pause and Ponder 7. Assertion (A): 2 g of hydrogen combines with 16 g of oxygen to form 18 g of water. Reason (R): According to Dalton’s Atomic Theory, atoms combine in a simple whole number ratio by mass to form compounds. Choose the correct option: (i) Both A and R are true, and R is the correct explanation of A. (ii) Both A and R are true, but R is not the correct explanation of A. (iii) A is true, but R is false. (iv) A is false, but R is true. Later, scientists discovered how atoms combine to form molecules. Let us explore further! 168 Exploration|Grade 9