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Which postulate of Dalton’s theory is consistent with the following observation concerning the weights of reactants and products? When 100 grams of solid calcium carbonate is heated, 44 grams of carbon dioxide and 56 grams of calcium oxide are produced.The following chemical change represented by these spheres may violate one of the ideas of Dalton’s atomic theory. If the spheres of different elements touch, they are part of a single unit of a compound. The purple spheres represent atoms of another element. In the following drawing, the green spheres represent atoms of a certain element.Are these data an example of the law of definite proportions, the law of multiple proportions, or neither? What do these data tell you about substances X and Y? A sample of compound Y (a clear, colorless, combustible liquid with a noticeable odor that is slightly different from X’s odor) is analyzed and found to contain 19.91 g carbon and 3.34 g hydrogen. Check Your LearningĪ sample of compound X (a clear, colorless, combustible liquid with a noticeable odor) is analyzed and found to contain 14.13 g carbon and 2.96 g hydrogen. A possible pair of compounds that would fit this relationship would be A = CO 2 and B = CO. This means that A and B are different compounds, with A having one-half as much carbon per amount of oxygen (or twice as much oxygen per amount of carbon) as B. This supports the law of multiple proportions. For example, when different samples of isooctane (a component of gasoline and one of the standards used in the octane rating system) are analyzed, they are found to have a carbon-to-hydrogen mass ratio of 5.33:1, as shown in Table 1. The suggestion that the numbers of atoms of the elements in a given compound always exist in the same ratio is consistent with these observations. This statement is known as the law of definite proportions or the law of constant composition. Law of Definite Proportionsĭalton knew of the experiments of French chemist Joseph Proust, who demonstrated that all samples of a pure compound contain the same elements in the same proportion by mass. This does not violate any of Dalton’s postulates: Atoms are neither created nor destroyed, but are redistributed in small, whole-number ratios. The products consist of four green spheres and two purple spheres.
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The starting materials consist of four green spheres and two purple spheres. A macroscopic sample of an element contains an incredibly large number of atoms, all of which have identical chemical properties. An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element (Figure 1).An atom is the smallest unit of an element that can participate in a chemical change. Matter is composed of exceedingly small particles called atoms.Here are the postulates of Dalton’s atomic theory. First published in 1807, many of Dalton’s hypotheses about the microscopic features of matter are still valid in modern atomic theory. The Aristotelian view of the composition of matter held sway for over two thousand years, until English schoolteacher John Dalton helped to revolutionize chemistry with his hypothesis that the behavior of matter could be explained using an atomic theory.
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Interestingly, these philosophers thought about atoms and “elements” as philosophical concepts, but apparently never considered performing experiments to test their ideas. Later, Aristotle and others came to the conclusion that matter consisted of various combinations of the four “elements”-fire, earth, air, and water-and could be infinitely divided. In the fifth century BC, Leucippus and Democritus argued that all matter was composed of small, finite particles that they called atomos, a term derived from the Greek word for “indivisible.” They thought of atoms as moving particles that differed in shape and size, and which could join together. The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers, the scientists of their day.