Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Section 4?t Objectives Compare and contrast the atomic models of Democritus, Aristotle, and Dalton. Understand how Dalton’s theory s. explains the conservation of mas Review Vocabulary theory: an explanation supported ject by many experiments; is still sub be can , data l enta to new experim sful modified, and Is considered succes s ion dict pre e mak to if it can be used that are true New Vocabulary Dalton’s atomic theory • Figure 4.1 Many Greek philosophers thought that matter was composed of four elements; earth, air, water, and fire. They also associated properties with each ele s, ment. The pairing of opposite propertie mir dr and wet and , cold and hot such as re. rored the symmetry they observed in natu and rrect inco e These early ideas wer non-scientific. 102 Chapter 4 • The Structure of the Atom Early Ideas About Matt,ebutrthe eeks tried to explain matter l’V1Ij The ancient Gr early began with John Dalton in the scientific study of the atom 1800s. eriment tball team might practice and exp Real-World Reading Link A foo they . As plan e develop the best-possible gam with different plays in order to the team’s ne ches can make adjustments to refi see the results of their plans, coa with different last 200 years have experimented play. Similarly, scientists over the . models as they collected new data models of the atom, refining their Greek Philosophers exist several thousand years ago. Science as we know it today did not few experiment was, and there were No one knew what a controlled nd mi the of er In this setting, the pow tools for scientific exploration. the to s sidered the primary avenue and intellectual thought were con as erest of scholarly thinkers known truth. Curiosity sparked the int cu y spe the As . life of s many mysterie philosophers who considered the d late mu for ers , many of the philosoph lated about the nature of matter life experiences. explanations based on their own matter was composed of things such Many of them concluded that wn in Figure 4.1. It was also com as earth, water, air, and fire, as sho r ld be endlessly divided into smalle monly accepted that matter cou no early ideas were creative, there was and smaller pieces. While these dity. method available to test their vali The Greek philosopher Democritus (460—370 Bc) infinitely :tpersonto propose the idea that matter was not particles individual tiny of made up was believed matter derived. Democritus is atom English word :s from which the be created, destroyed, or further divided. “t atoms could not his ideas are shown in Table 4.1. of summarY ritus and a 1 ve1 s ideas do not agree with modern DemocrituS’ a number of his belief in the existence of atoms was amazingly ahead a’Ic theorY, met with criticism from other time. However, his ideas were the atoms together?” Democritus holds “What asked, iii1osoph who question. gould not answer the Aristotle (384—322 B.C.), one Aristotle Other criticisms came from . He rejected the notion of philosophers Greek of the most influential with his own ideas about nature. One of atoms because it did not agree Aristotle’s major criticisms concerned the idea that atoms moved through empty space. He did not believe that empty space could exist. of His ideas are also presented in Table 4.1. Because Aristotle was one the most influential philosophers of his time, Democritus’s atomic theory was eventually rejected. In fairness to Democritus, it wa impossible for him or anyone else of his time to determine what held the atoms together. More than two thousand years would pass before scientists would know the answer. However, it is important to realize that Dernocritus’s ideas were just that—ideas, not science. Without the ability to conduct controlled experiments, Democritus could not test the validity of his ideas. Unfortunately for the advancement of science, Aristotle was able to gain wide acceptance for his ideas on nature—ideas that denied the existence of atoms. Incredibly, the influence of Aristotle was so great and the development of science so primitive that his denial of the existence of atoms went largely unchallenged for two thousand years! tL5 VOCABULARY WORD ORIGIN Atom comes from the Greek word atomos, meaning indivisible Reading Check Infer why it was hard for Democritus to defend his ideas. Table 4.1 Ancient Greek Ideas About Matter Ideas opher 1 i Matter is composed of atoms, which move through empty space. Atoms are solid, homogeneous, indestructible, and indivisible. Different kinds of atoms have different sizes and shapes. Size, shape, and movement of atoms determine the properties of matter. Democritus (460—370 B.C.) • • • • Aristotle • Empty space cannot exist. • Matter is made of earth, fire, ai and water. (384-322 B.C.) Section 4.1 • Early Ideas About Matter 103 Dalton’s Atomic Theory Table 4.2 Ideas Scientist — atoms. Matter is composed of extremely small particles called . Atoms are indivisible and indestructible and chemical properties. Atoms of a given element are identical in size, mass, e of another element. Atoms of a specific element are different from thos to form compounds. r ratios Different atoms combine in simple whole-numbe bined or rearranged. In a chemical reaction, atoms are separated, com • • • • • • Dalton (1766-1844) - ed in the was reviv John Dalton Although the concept of the atom re significant befo s year red eighteenth century, it took another hund ry by John centu h teent progress was made. The work done in the nine the beginning s and, mark Dalton (1766—1844), a schoolteacher in Engl on revived and of the development of modern atomic theory. Dalt tific research he scien of ts resul revised Democritus’s ideas based on the are similar. ideas on’s conducted. In many ways, Democritus’s and Dalt Dalton day, ocritus’s Thanks to advancements in science since Dem to refine and support was able to perform experiments that allowed him ions, malcing care react ical his hypotheses. He studied numerous chem was able to deter He way. ful observations and measurements along the in those reactions. The mine the mass ratios of the elements involved atomic theory, which he results of his research are known as Dalton’s ry are summarized in proposed in 1803. The main points of his theo book, an extract of which is Table 4.2. Dalton published his ideas in a shown in Figure 4.2. us’ and Dalton’s Reading Check Compare arid contrast Democrit ideas. F%.e, 4 • Figure 4.2 In his book A New System of Chemical Philosophy, John Dalton presented his symbols for the elements known at that time and their possible combinations. J 00 0000 thé6éé óàôàà th I 000 0 L 17 I!) JO 00/00 ®óo oàooéo /D0. . •• .. •. :• •. Atoms of Element A Total mass = 4(Mass A) ‘I -. Atoms of Element B Total mass = 8(Mass B) p Compound composed of Elements A and B Total mass = 4(Mass A) + 8(Mass B) atoms of two or more elements combine to form a compound, • Figure 4.3 When element is conserved. Thus, the mass is conserved as well. each of atoms of the number Con5e1Iatb0I of mass Recall from Chapter 3 that the law of con servation of mass states that mass is conserved in any process, such as a chemical reaction. Dalton’s atomic theory easily explains that the con servation of mass in chemical reactions is the result of the separation, combination, or rearrangement of atoms—atoms that are not created, destroyed or divided in the process. The formation of a compound from the combining of elements and the conservation of mass during the process are shown in Figure 4.3. The number of atoms of each type is the same before and after the reaction. Dalton’s convincing experimental evidence and clear explanation of the composition of compounds, and conservation of mass led to the general acceptance of his atomic theory. Dalton’s atomic theory was a huge step toward the current atomic model of matter. However, not all of Dalton’s theory was accurate. As is often the case in science, Dalton’s theory had to be revised as additional information was learned that could not be explained by the theory. As you will learn in this chapter, Dalton was wrong about atoms being indivisible. Atoms are divisible into several subatomic particles. Dalton was also wrong about all atoms of a given element having identical properties. Atoms of the same element can have slightly different masses. Section 4I Asses Section Summary I Democritus was the first person to propose the existence of atoms. I According to Democritus, atoms are solid, homogeneous, and indivisible. I Aristotle did not believe in the existence of atoms. I John Dalton’s atomic theory is based Ofl numerous scientific experiments. Ch enst line 1. iriic Contrast the methods used by the Greek philosophers and Dalton to study the atom. 2. Define atom using your own words. 3. Summarize Dalton’s atomic theory. 4. Explain how Dalton’s theory of the atom and the conservation of mass are related. 5. Apply Six atoms of Element A combine with eight atoms of Element B to pro duce six compound particles. How many atoms of Elements A and B does each particle contain? Are all of the atoms used to form compounds? 6. Design a concept map that compares and contrasts the atomic ideas proposed by Democritus and John Dalton. Self-Check Quiz lencoe.corn Section 4.1 • Early Ideas About Matter 105