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
Grade 11 Unit 4 SCIENCE 1104 ATOMIC STRUCTURE AND PERIODICITY CONTENTS I. CONTRIBUTORS TO A CONCEPT . . . . . . . . . . 2 DEMOCRITUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . JOHN DALTON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. J. THOMSON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MARIE CURIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ERNEST RUTHERFORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NIELS BOHR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ERWIN SCHRODINGER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . JAMES CHADWICK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 8 9 10 12 14 15 II. MODERN ATOMIC STRUCTURE . . . . . . . . . . . 21 ATOMIC SPECTRA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 BOHR MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 MODERN MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 III. ATOMIC PERIODICITY . . . . . . . . . . . . . . . . . . . 47 PERIODIC LAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 DMITRI I. MENDELEEV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 IV. NUCLEAR REACTIONS . . . . . . . . . . . . . . . . . . . 55 NATURAL RADIOACTIVITY . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 NUCLEAR ENERGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Author: Editor: Illustrators: Harold Wengert, Ed.D. Alan Christopherson, M.S. Alpha Omega Graphics 804 N. 2nd Ave. E., Rock Rapids, IA 51246-1759 © MM by Alpha Omega Publications, Inc. All rights reserved. LIFEPAC is a registered trademark of Alpha Omega Publications, Inc. All trademarks and/or service marks referenced in this material are the property of their respective owners. Alpha Omega Publications, Inc. makes no claim of ownership to any trademarks and/or service marks other than their own and their affiliates’, and makes no claim of affiliation to any companies whose trademarks may be listed in this material, other than their own. ATOMIC STRUCTURE AND PERIODICITY are all the other isolated elements what they are and why are they separated from one another? Why are they found where they are found and what accounts for their peculiar qualities? Scientists thought they had succeeded in breaking down matter to its last ultimate unit: that is, the atom. In an article which appeared in a national magazine, a writer on this subject was introduced by the editor of that magazine as “one of the nation’s foremost interpreters of modern science.” This modern authority on science then wrote that the Greeks knew the atom but they did not know what we know about the atom nor of its infinite smallness. Then this writer continues by making a startling statement asserting that a teaspoonful of water contains a million billion trillion atoms. We can repeat these figures, but no one can comprehend what they mean. And this writer then says, “We now have learned that this infinitely tiny atom is composed of still smaller parts which form a microscopic universe in which there is action, energy and motion similar to that of our own solar system. In everyday language we speak of dead matter, and, of course, it is dead in the sense that it does not have in it what we call the germ of life, nor can it propagate itself. But it is not dead in the sense that it is inactive or absolutely static. In a lump of socalled dead matter, there are countless billions of atoms, each one an active universe, a bundle of energy and force beyond all comprehension, as we have learned since the atomic bomb has come into existence.1 Genesis 1:1 states: “In the beginning God created the heavens and the earth.” What does this verse mean? Dr. Alfred M. Rehwinkel in his book, The Wonders of Creation, gives us his explanation. In view of what occurred on the six days of the creation week, the heaven and the earth in this connection can only mean that on the first day God began by the creation of matter out of which He formed the things that were made on the days that followed. God began the creation by first providing himself with the material out of which all other things were formed. Matter is not eternal, as the ancient Greek philosophers and the modern evolutionists assume. Matter had its beginning with God; He created it out of nothing; We first filled the absolute vacuum of nothingness with raw, unsystematized matter. There is no other possible source for the origin of matter. Dead matter could not have created itself. But that raises the next important question: namely, What is matter? What is the essence of the substance out of which heaven and earth were made? On the one hand, matter might be defined as a combination of a number of chemical substances which combined according to very specific laws to form that something which we call matter, but that leads to the next question: that is, What is the origin of the individual chemical substances which are combined to form matter? How did the laws come into being which cause them to combine in a given order? Science has isolated over a hundred separate substances which are basic or simple and do not consist of combinations of other substances, but how did they come to be just what they are? Why is gold gold, and silver silver, and uranium uranium, and why This LIFEPAC® will guide our exploration of the history of atomic theory and develop some ideas about our modern model of the atom. OBJECTIVES Read these objectives. The objectives tell you what you will be able to do when you have successfully completed this LIFEPAC. When you have finished this LIFEPAC, you should be able to: 1. Develop a time-event sequence leading to our present atomic model. 2. Identify eight key scientists and explain their contributions to atomic theory. 3. Develop the theory of modern atomic structure. 4. Develop and explain the periodicity of atomic structure. 5. Explain nuclear reactions. Rehwinkel, Alfred M. The Wonders of Creation; Bethany Fellowship, Inc. Minneapolis, Minnesota, 1974, pages 50-51. 1 1 I. CONTRIBUTORS TO A CONCEPT This section is designed to help you get a better idea and appreciation for eight scientists who made great contributions to the development of our present-day atomic theory. Information on each scientist is taken from the “Atomic Pioneer Series.” United States Energy Research and Development Administration Technical Information Center Oak Ridge, TN 37830 The three-volume set is available from ERDA. SECTION OBJECTIVES Review these objectives. When you have completed this section, you should be able to: 1. Develop a time-event sequence leading to our present atomic model. 2. Identify eight key scientists and explain their contributions to atomic theory. 2.1 Identify and locate the three main particles of atoms. 2.2 Use the atomic mass and atomic numbers of the different elements. VOCABULARY Study these words to enhance your learning success in this section. alpha particle atomic mass atomic number beta particle electrons gamma ion isotopes neutrons nucleus protons quantum radioactive spectrum DEMOCRITUS Democritus was the world’s first great atomic philosopher. He was born in Abdera, Thrace, around 460 B.C. and died, place unknown, about 380 B.C. ter consisted of particles so small that nothing smaller could be imagined. These particles were indivisible. The word atom itself means that which cannot be cut. These atoms were eternal, unchangeable, and indestructible. They differed from each other in physical shape, and this difference allowed them to form different substances. Democritus’ theory of atoms led him to expound an explanation of the world that was completely mechanical. He reasoned that no such thing as spirit existed apart from matter. He postulated special “soul” atoms. The universe was the blind result of swirling atoms. Through their motions these atoms clumped together to form worlds. Biographical details. After studying under Leucippus in Abdera, Democritus resolved to spend his inheritance in research abroad. He traveled widely, studying in Egypt for five years and then journeying to Chaldea, Babylon, Persia, and possibly to India. Democritus was interested in all branches of knowledge and specialized in mathematics, astronomy, and medicine. He lived in the shadow of another Greek philosopher, Socrates. Democritus once visited Athens and saw Socrates, but he was too shy to introduce himself. He wrote many books, but they did not survive. We know of them because of references made to them by other writers. His interest in ethics led him to write proverbs, the accumulated wisdom of his people. He was a cheerful lover of knowledge, and he lived to the age of eighty. Contribution to atomic science. Although long overshadowed by Socrates, his contemporary, Democritus nevertheless was the most successful of the Greek philosopher-scientists in the correctness of his theories. In line with the Greek basis of knowledge, his ideas were derived from deductive reasoning, not from experimenting and testing. Yet his view of the world was much closer to our twentieth-century concepts than the views of most other Greek philosophers of that time. Scientific achievements. For Democritus, the world was made of only two things: the vacuum of empty space and the fullness of matter. All mat2 Answer these questions. 1.1 Who was the first to propose the idea of atoms? __________________________________________ 1.2 In what century was the concept of atoms first proposed? _________________________________ 1.3 What was Democritus’ academic preparation ____________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ 1.4 How did Democritus account for differences in matter? ___________________________________ ___________________________________________________________________________________ 1.5 Who was Democritus’ famous contemporary? ____________________________________________ JOHN DALTON John Dalton, an English chemist, was born in Eaglesfield, Cumberland, England, on September 6, 1766, and died in Manchester on July 27, 1844. He is considered the father of modern atomic theory. Biographical details. Dalton was the son of a poor weaver. His parents were Quakers (Society of Friends) and he was a devout member of that faith. He received his early education from his father and at a Quaker school in his hometown. When his teacher retired, Dalton replaced him. He was then twelve years old. He remained a teacher most of his life. When he was twenty-seven, he moved to Manchester and taught college until the college was moved. He then became both a public and private teacher of mathematics and chemistry, and he worked in his laboratory when he was not teaching. Scientific achievements. Dalton’s first scientific work was in meteorology. He kept weather records for fifty-seven years. He wrote a book about weather when he was twenty-seven years old. In his work, Dalton deduced that gases were composed of particles of matter, just as he thought solids were. He also made the first study of color blindness, a subject of personal interest since he himself was color blind. His lasting work was in the field of atomic chemistry. He studied Newton and Boyle and experimented with gases and Proust’s Law of Definite Proportions. The Law of Definite Proportions states that substances combine in predictable proportions. When excess reactants are used, the excess becomes leftovers. Figure 1: The Law of Definite Proportions states that when excess reactants are used, the excess is not combined and becomes “leftovers.” 3 Figure 2: The Law of Definite Proportions Interpreted in Terms of Dalton’s Atomic Symbols He formulated his own law of multiple proportions in 1803, based on his observation that the same elements combine in different proportions to produce different substances. Figure 3: The Law of Multiple Proportions He proposed his atomic theory and published his ideas in a book, New Systems of Chemical Philosophy in 1808. He maintained that all matter is made of invisible atoms, that atoms are alike in everything except their mass (or weight), that in chemical reactions atoms preserve their identity and are not destroyed, and that only whole atoms may combine. Figure 4: According to Dalton’s atomic theory, only whole atoms may combine. The second scheme is not possible. 4 He tried to work out the relative masses of atoms; but his calculations were wrong, although the principle was correct. He was, however, the first to establish a table of atomic masses, with hydrogen, the lightest atom, as the standard. ic hypothesis from Democritus and Newton to his own day, primarily because he based his theory on scientific observation rather than on philosophical speculation. After Dalton’s work was published, it was widely accepted in a short time and eventually his atomic theory became the basis of all chemistry. Contribution to atomic science. Dalton occupies an important place in the history of atom- Answer this question. 1.6 Who is considered the father of atomic theory? __________________________________ Explain this activity. 1.7 Law of Multiple Proportions ____________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 1.8 Law of Definite Proportions ____________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 1.9 Dalton’s model of the atom ____________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Do this exercise. These supplies are needed: 9 samples of pure elements (sulfur powder, zinc powder, magnesium ribbon, iron, copper, lead, silver, etc.) reference textbook Science LIFEPAC 1103 a chemistry handbook Follow these directions and record your data in the table. Place a check in the box when the step is completed. ❏ 1. Get some samples of pure elements from the shelf or from your teacher. ❏ 2. From the observations you can make and with the use of a handbook, reference text, and Science LIFEPAC 1103, complete the following chart of properties. 5 Data Table 1 Element Symbol Physical State at 25°C Color Magnetic Yes or No Atomic Mass Other Properties Adult check ___________________ Initial Date As is obvious from the preceding data table, the elements are all different. Apparently then, the atoms that make up the elements must be all different. The macroscopic properties we saw and measured in the previous exercise are really the sum of the properties of the individual atoms. Let’s investigate a few more properties of four specific elements. Try this experiment. These supplies are needed: tin can lid with 4 indentations support stand and ring bunsen burner or propane burner sample of iron, copper, magnesium, and lead Follow these directions and answer the questions. Place a check in the box when the step is completed. ❏ ❏ ❏ ❏ ❏ 1. 2. 3. 4. 5. Secure the ring stand and ring. Place the lid on the ring. Place a peg-sized piece of a solid element in each indentation. Heat each from above with the lighted burner. Record all observations in the data table. 6 Cu Data Table 2 Pb Mg Fe Observation before Heating Observation during Heating Observation when Cool Again Complete these activities. 1.10 Burning can be described as the combining with oxygen to form new products. Are these products of burning the four elements the same? _______________ 1.11 Do all four of the elements combine with oxygen in the same way? _______________ 1.12 Explain your answers in 1.10 and 1.11. _________________________________________________ ______________________________________________________________________________________ ______________________________________________________________________________________ Try this experiment. These supplies are needed: 2 vinyl strips 2 acetate strips masking tape 2 40-cm nylon strings ❏ ❏ ❏ ❏ ❏ 1.13 1.14 1.15 1.16 1.17 1.18 Follow these directions and answer the questions. Place a check in the box when the step is complete. 1. Thoroughly wash and blot dry the vinyl and acetate strips. 2. Near one end label the vinyl strips V-1 and V-2. 3. Near one end label the acetate strips A-1 and A-2. 4. Fasten separate 40-cm nylon strings to the center of V-1 and A-1. 5. Hang these strips from a table or chair so they are free to move around in a circle. What happens when the unmarked end of V-2 is brought near the unmarked end of V-1? _______________________________________________________________________________________ What happens when the unmarked end of V-2 is brought near the unmarked end of A-l? _______________________________________________________________________________________ What happens when 1.13 and 1.14 are repeated with A-2 instead of V-2? _______________________________________________________________________________________ Now rub the unmarked ends of both vinyl strips with woolen cloth, first V-1 and then V-2. Bring the two rubbed ends near each other. Do they repel or attract? _______________________________________________________________________________________ Rub the unmarked ends of A-1 with tissue paper and V-2 with wool cloth. Bring the two rubbed ends together. Did they attract or repel? __________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Reverse the process in 1.17 and use A-2 and V-1. Did the two strips attract or repel? _______________________________________________________________________________________ 7 1.19 From your data and observations complete the following summary: Combination Attract or Repel V-1 and V-2 a. ______________________________ V-1 and A-2 b. ______________________________ A-1 and V-2 c. ______________________________ A-1 and A-2 d. ______________________________ 1.20 a. Since the same procedure was used to charge both vinyl strips does each have the same charge? __________ b. Do both acetate strips have the same charge? __________ c. Do the acetate strips have the same charge? __________ d. Do like charges attract or repel? __________ e. Do unlike charges attract or repel? ____________________ 1.21 Experiments have consistently shown that the acetate strip is positive (+) and the vinyl strip is negative (–). Restate the idea of 1.20 in terms of positives (+) and negatives (–). _______________________________________________________________________________________ _______________________________________________________________________________________ 1.22 a. How many different kinds of electricity do you think the above evidence suggests? ____________________ b. Explain. ___________________________________________________________________________ ___________________________________________________________________________________ J.J. THOMSON Joseph John Thomson, British physicist and discoverer of the electron, was born at Cheetham Hall near Manchester on December 18, 1856, and he died in Cambridge on August 30, 1940. inside the tube. He measured the deflections in magnetic and electrical fields and showed that the rays were streams of negatively charged particles. Thomson did not measure the size of the negative charge; that discovery was left to Robert Millikan after 1910. Then Thomson measured the ratio of the charge of the cathode-ray particles to their mass. He concluded that if the charge was equal to the minimum charge of ions, then the mass of the particles was only a small fraction of the mass of a hydrogen atom and that the cathode-ray particles, electrons, were smaller than atoms. For this discovery he was awarded the 1906 Nobel Prize in physics. Biographical details. Thomson entered college at fourteen. When he was only twenty-seven years old, he succeeded Lord Rayleigh as professor of physics at Cambridge University. He became head of the Cavendish Laboratory and guided it into leadership in the field of subatomic physics for over thirty years. In 1908 he was knighted. He was a gifted leader, and seven of his research assistants were themselves awarded Nobel Prizes. His son and pupil, Sir George Paget Thomson, also won the Nobel Prize in physics in 1937. Thomson died just before World War II and was buried near Isaac Newton in Westminster Abbey. Figure 5: The Thomson Model of the Atom: the “Raisin Pudding” Model. Scientific achievements. In 1895 Thomson began to investigate the mysterious rays emitted when electricity passes through an evacuated glass tube. Because they originated from the cathode, the negative electrical pole in the tube, the rays were called cathode rays. No one had succeeded in deflecting them by an electric field. Other scientists believed that cathode rays were like light waves, but Thomson believed them to be tiny particles of matter. He built a cathode-ray tube in which the rays became visible as dots on a fluorescent screen 8 Thomson had opened the door to research on subatomic particles. He believed the electron was a universal component of matter and suggested that the internal structure of the atom was a positively charged space with electrons sprinkled throughout, much like raisins sprinkled through pudding. Thomson engaged in another important discovery with his work on “channel rays,” which are streams of positively charged ions. He deflected these rays by magnetic and electric fields and found that ions of neon gas fell on two different spots of a photographic plate, as though they were a mixture of two types that differed in charge or mass or both. This finding was his first indication that nonradioactive elements might have isotopes: atomic varieties of a single element, which differ only in their mass. Contribution to atomic science. Thomson’s work on cathode rays proved the existence of the electron and led to the study of subatomic particles. Furthermore, when he discovered how to identify isotopes of the chemical element neon 20 and neon 22, he showed scientists that nonradioactive isotopes existed. Complete these activities. 1.23 1.24 1.25 1.26 Describe Thompson’s concept of the atom. _______________________________________________ _______________________________________________________________________________________ Name the apparatus Thomson used to detect electrons. ___________________________________ Describe the difference between neon 20 and neon 22. ____________________________________ _______________________________________________________________________________________ Prior to Thomson’s discovery, electric charge was thought to occur in an infinite range. Explain the significance of Thomson’s concept of the electron. _____________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ MARIE CURIE Marie Sklodowska Curie, a Polish-French chemist, is the only person to have won two Nobel Prizes in science. She was born in Warsaw, Poland, on November 7, 1867, and died in Haute Savoie, France on July 4, 1934. who, with her husband Frederic Joliot, would win the 1935 Nobel Prize in chemistry. When Pierre was killed in a street accident in 1906, he was succeeded as professor of physics at the Sorbonne by Marie, the first woman ever to teach there. She overcame many professional obstacles, but she could not overcome all prejudices against women working as scientists. Though she was nominated to the French Academy, she lost by one vote because she was a woman. However, in 1911 she was awarded another Nobel Prize in chemistry for research that she and Pierre had done in the discovery of radium and of polonium, which she named for her native Poland. In World War I she interrupted her work to drive an ambulance on the battlefields of France. After the war, she spent her years supervising the Paris Institute for Radium, which she founded. In honor of Marie and Pierre Curie, the quantity of any radioactive substance that emits particles at the same rate as does one gram of radium (37 billions per second) is called a curie. Biographical details. Marie Sklodowska’s father was a Polish physics teacher and her mother was the principal of a girls’ school. When her parents died, she followed her older brother and sister to Paris. She enrolled at the Sorbonne, living an impoverished existence but graduating at the top of her class. In 1894, she met the French chemist, Pierre Curie. They married a year later on July 26, 1895. The two became fascinated with the discoveries of Xrays by Roentgen and of radioactivity by Becquerel. Pierre abandoned his own research, and for the final seven years of his life, he served as his wife’s collaborator. Together they studied radioactivity in uranium and isolated two new elements, radium and polonium, for which they received the 1903 Nobel Prize in physics jointly with Becquerel. The Curies lived modestly, using all their earnings to pay for shipping tons of waste ore, rich in uranium, from abandoned mines in Bohemia to the physics school where they conducted their research. They had two daughters. One was Irene, a scientist Scientific achievements. After the discovery of X-rays, the Curies undertook a systematic study of the radioactive properties of pitchblende, an ore of uranium. Applying Pierre’s discovery of piezoelectricity to the measurement of radioactivity in uranium, 9 In July, 1898, after years of grueling experiments in their shed, they isolated a tiny amount of a new, intensely radioactive element, which they named polonium. In December, 1898, they discovered another intensely radioactive substance, radium in such small quantities that it could be detected only as a trace impurity. Now they wanted to produce radium in visible quantities, and for four years they purified tons and tons of ore into small samples of pure radium. By 1902 they had prepared a tenth of a gram of radium from all the tons of uranium shipped to their laboratory. they found that some uranium ore must contain elements much more radioactive than uranium. They performed these experiments in a wretched little shed that the School of Physics had given them. It was suffocatingly hot in summer, brutally cold in winter, and the roof leaked. Their precision instruments were often affected by the humidity and the temperature changes. Marie Curie had said of this time,”… And yet it was in this miserable old shed that the best and happiest years of our life were spent, entirely consecrated to work. I sometimes passed the whole day stirring a mass in ebullition, with an iron rod nearly as big as myself. In the evening I was broken with fatigue. In our poor shed there reigned a great tranquillity: sometimes, as we watched over some operation, we would walk up and down, talking about work in the present and in the future; when we were cold, a cup of hot tea taken near the stove comforted us. We lived in our single preoccupation as if in a dream.” Contribution to atomic science. The discovery of radium and polonium by Marie and Pierre Curie and their research on radioactivity laid the foundation for new discoveries in nuclear physics and chemistry. Scientists would follow close on their trail to discover other radioactive elements. Complete these activities. 1.27 1.28 1.29 1.30 1.31 An ore of uranium is ______________________________ . The discoverer of X-rays was a. ____________________________________ , and the discoverer of radioactivity was b. _____________________ . The two elements isolated by the Curies were a. ____________________________________ and b. ____________________________________ . The school in Paris at which Marie Curie was the first woman teacher was ________________ ____________________ . The achievements of which Pierre and Marie Curie were awarded Nobel Prizes were the a. ______________________________ and the b. ______________________________ . ERNEST RUTHERFORD Ernest Rutherford, a British physicist whose contributions to science of the theory of the nuclear atom brought him the title, “father of nuclear science.” He formulated the theory of radioactive disintegration of elements, identified alpha and beta particles, and devised the theory of the nuclear structure of the atom. He was born on a farm near Nelson, New Zealand, on August 30, 1871, and died in London on October 19, 1937. Manchester University and Cambridge where he remained until his death. He won many honors for his scientific achievements. He was knighted in 1914, and in 1931 was named First Baron Rutherford of Nelson. Scientific achievements. Rutherford’s great contributions to science began at McGill University with work in the field of radioactivity. There he reported on the discovery that rays given off by radioactive substances are of several different kinds. He called the positively charged ones alpha rays and the negatively charged ones beta rays. The names are still used, but today the rays are known to be speeding particles and are called alpha particles and beta particles. When Paul Villard discovered in 1900 that some rays were not affected by a magnetic field, Rutherford proved that these consisted of electromagnetic waves, which he called gamma rays. Biographical details. Rutherford was the son of a wheelwright and farmer. As a child he helped his father dig potatoes on the farm. He was a promising student and won scholarships to Canterbury College in New Zealand and to Cambridge University in England, where he worked under J. J. Thomson. At McGill University in Montreal from 1898 to 1907, Rutherford continued work he had begun in the field of radioactivity. Then he returned to 10 Figure 6: Rutherford Gold Foil Experiment. Notice that the particles (bullets) are scattered but most go right on through the “solid” gold foil. Rutherford and Frederick Soddy collaborated in research on radioactive disintegration. They believed that, starting with uranium, each radioactive element decays, or breaks down, into a daughter element, and that this daughter element breaks down into another, and so on. The last element formed is lead. Figure 7: Rutherford’s Gold Foil Experiment Rutherford began to study how alpha particles are scattered by thin metallic sheets. When he fired alpha particles at gold foil, most of the particles passed through unaffected. Some of them, however, scattered at large angles, which meant that somewhere in the foil was a massive charged region that deflected the positively charged alpha particles. Rutherford said this finding was “almost as incredible as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you.” Rutherford went to Manchester University in 1909 and established a center for the study of radioactivity. He proved that the alpha particle was a helium atom with its electrons removed. (Later he said that the simplest positive rays must be those obtained from hydrogen and that these must be a fundamental positively charged particle, which he called a proton.) From this research Rutherford evolved the nuclear theory, the greatest of all his contributions to physics. He suggested that the atom contains a very tiny nucleus at its center, which is positively charged and contains all the protons of the atom and therefore almost all its mass. Very light negatively charged electrons, posing little barrier to alpha particles passing through the atom, make up the outer regions. His was dubbed the “open spaces” model. In 1908 Rutherford won a Nobel Prize for “his investigations of the chemistry of radioactive substances.” In a letter to his mother he said that the prize was very acceptable, “both as regards honour and cash.” The nuclear theory was not Rutherford’s sole contribution to science. With Hans Geiger he used a scintillation counter to measure radioactivity. They counted the flashes (scintillations), each of which signified an emitted particle, on a zinc sulfide screen and determined that a gram of radium emitted 37 billion alpha particles a second. This fact is the basis for the unit called the curie. In 1917 Rutherford resumed his research in nuclear models. In 1919 he succeeded in disintegrating nitrogen nuclei by alpha particle bombardment, producing charged hydrogen atoms and oxygen at the same time. With this act he accomplished the first man-made “nuclear reaction,” and by 1924 Rutherford accomplished the feat of knocking the protons out of nuclei in most of the lighter elements. Rutherford was a marvelous teacher and infected his students with his own enthusiasm for scientific research. (Among his many illustrious students were Ernest Marsden, Hans Geiger, Ernest Walton, James Chadwick, Francis Aston, John Cockcroft, Henry Moseley, Otto Hahn, and Frederick Soddy.) His students said of him, “He had none of the meaner faults and was just as willing to attend to the youngest student and if possible learn from him as … to listen to any recognized scientific authority. He made us feel as if we were living very near the center of the scientific universe.” He had a short temper, which he sometimes displayed when experiments were not going to his satisfaction. When things ran along smoothly, he would walk through the laboratory singing “Onward Christian Soldiers.” Contribution to atomic science. Lord Rutherford contributed the theory of the basic 11 structure of the atom itself. In addition he was the first scientist in history to produce man-made atomic disintegration, when he bombarded nitrogen atoms with alpha particles and produced protons. Fellow scientist Niels Bohr said when Rutherford died that he, like Galileo, “left science in quite a different state from that in which he found it.” A physicist once said to Rutherford, “You are a lucky man…always on the crest of the wave!” “Well,” Rutherford remarked, “I made the wave, didn’t I?” Complete these activities. 1.32 1.33 1.34 1.35 1.36 1.37 1.38 Name the renowned professor under whom Rutherford studied at Cambridge University. _________________________ Rutherford named three kinds of radioactive emissions. List the emissions and describe them. a. emission: __________________________________________________________________________ b. description: ________________________________________________________________________ a. emission: __________________________________________________________________________ b. description: ________________________________________________________________________ a. emission: __________________________________________________________________________ b. description: ________________________________________________________________________ Describe the hypothesis produced by the research of Rutherford and Soddy. ________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Describe the gold foil experiment which led Rutherford to the discovery of the atomic nucleus. ___________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ Name the device used for scintillation counting. _________________________________________ NIELS BOHR Niels Bohr, a Danish physicist, helped develop the field of quantum physics. He was awarded the Nobel Prize in physics in 1922 for his atomic theory, which laid the groundwork for later atomic research. He was born on October 7, 1885, in Copenhagen, Denmark and died there November 18, 1962. From Sweden, Bohr came to the United States where he participated in the Los Alamos atomic bomb project. He helped organize the first United Nations Atoms-for-Peace Award two years later. Scientific achievements. Bohr showed an early talent for physics. At the age of twenty-two, he won a gold medal for determining the surface tension of water. Working with Rutherford, Bohr studied that scientist’s nuclear model of the atom. In 1913 he combined the Rutherford nuclear atom with the quantum theory of Max Planck to explain how atoms emitted and absorbed ultraviolet light and infrared energy. Studying the hydrogen atom, he concluded that electrons move in orbits around the atomic nucleus. As long as an electron remains in a given orbit, no energy is radiated. However, a suitable energy source can cause the electron to jump to an orbit of higher energy. When the electron returns to the lower orbit, the extra energy is liberated as a single quantum (specified quantity) of light or other form of radiation. Biographical details. Bohr studied physics at the University of Copenhagen and received his doctorate in 1911. He went to Manchester University and worked under Rutherford until he returned to the University of Copenhagen as physics professor. In 1920 Bohr became head of the newly created Institute of Theoretical Physics in Copenhagen, and he held this position until his death. By the 1920s his institute had become a world center of atomic physics. There his interpretations of quantum theory were developed. In 1940 Denmark was occupied by the Germans, and Bohr fled by fishing boat to Sweden. When he escaped, he carried with him his Nobel medal made of gold, which he had melted down in order to carry it inconspicuously. After the war he had the medal recast into its original form. 12 Figure 8: Three Different Models of the Nitrogen Atom Each type of radiant energy is transmitted in waves with a certain range of frequencies. Bohr derived equations for calculating the frequencies of the lines in the spectrum of the hydrogen atom. Bohr was unable to apply his theory to calculate the spectrum of atoms more complex than hydrogen; but he pointed out that in elements heavier than hydrogen, those possessing more than one electron, the electrons exist in shells, and the electron content of the outermost shell determines the chemical properties of the element. After Meiter’s and Frisch’s theory of uranium fission was announced in 1939, Bohr correctly predicted that the isotope uranium 235 was the fissionable isotope. finally transmuted the enterprise. It was a period of patient work in the laboratory, of crucial experiments and daring action, of many false starts and many untenable conjectures, of debate, criticism, and brilliant mathematical improvision. For those who participated, it was a time of creation; there was terror as well as exaltation in their new insight. It will probably not be recorded very completely as history. As history, its re-creation would call for an art as high as the story of Oedipus or the story of Cromwell, yet in a realm of action so remote from our common experience that it is unlikely to be known to any poet or historian.” The Bohr model had problems, however. Because your radio picks up static from overhead wires or from an electric mixer, you know that an accelerating electrical charge emits energy. You may also know that any object in circular motion is accelerating because the direction of its velocity is changing. When these two bits of knowledge are put together, the conclusion is that orbiting electrons should emit energy. However, orbiting electrons do not emit energy unless they change orbits. If orbiting electrons did emit energy, every object in your room would foul radio reception; and rather quickly every atom would lose all its energy and collapse in on its nucleus, leaving just a very small pile of dust. This conclusion is the origin of a recurring problem: Do classical laws of physics and chemistry— Newtonian laws of motion, for example—apply to atomic particles? Contribution to atomic science. Bohr applied quantum theory to explain the hydrogen spectrum. Later he prepared a scheme for the arrangement of electrons in various atoms on the basis of their radiation spectra. J. Robert Oppenheimer summed up Bohr’s contribution in this way: “Our understanding of atomic physics, of what we call the quantum theory of atomic systems, had its origins at the turn of the century and its great synthesis and resolutions in the nineteen-twenties. It was a heroic time. It was not the doing of any one man; it involved the collaboration of scores of scientists from many different lands, though from first to last the deeply creative and subtle critical spirit of Niels Bohr guided, restrained, deepened, and Do these activities. 1.39 Name the famous atomic physicist under whom Niels Bohr studied at Manchester University. _______________________________________________________________________________________ Thomson and Rutherford had each contributed a small bit of understanding to the structure of the invisible atom. Summarize their contributions to the atomic model and describe the addition made by Niels Bohr. 1.40 Thomson. _____________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 13 1.41 Rutherford ____________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 1.42 Bohr _________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 1.43 Explain why the Rutherford-Bohr model is aptly called the planetary atom. _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 1.44 Describe the cause of light emission from atoms. _________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ 1.45 Draw one logical inference about emitted light from these statements: a. Orbits in any given element are fixed energy levels. b. The frequency (color) of emitted light is related to its energy. ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ ERWIN SCHRODINGER Erwin Schrodinger (shroi ding er), an Austrian physicist, shared the Nobel Prize in physics in 1933 with P. A. M. Dirac for their new atomic theory, which included wave mechanics and prediction of the positron. He was born on August 12, 1887, in Vienna, Austria, and died there on January 4, 1961. of several specific orbits. Around each of these electrons, matter waves spread out in a specified number of wave lengths. For any given element, electrons exist only in certain orbits. In the late 1920’s, Schrodinger derived the mathematical basis for this idea, which is called wave, or quantum, mechanics. Biographical details. Schrodinger was educated at the University of Vienna. When World War I broke out, he fought as an artillery officer and then settled in Germany after the war. He taught physics at several universities and in 1927 succeeded Max Planck as professor of theoretical physics at the University of Berlin. In the early 1930’s he interceded during a Nazi raid on a Jewish ghetto. He would have been beaten to death, except that one of the Storm Troopers recognized him and prevented the attack. When the Nazi rise to power became inevitable, Schrodinger returned to Austria. When Germany annexed Austria, Schrodinger fled to Ireland and taught at the Institute of Advanced Studies in Dublin. In 1956 he returned to Vienna and remained there until his death in 1961. Contribution to atomic science. De Brogile had postulated that matter at the atomic level possessed characteristics of both particles and waves. In addition to the matter being minute, it had to be moving at speeds near the speed of light. Based on this idea, Schrodinger expressed the behavior of a particle with a mathematical equation for wave motion. By combining this mathematical equation with the quantum theory, the Schrodinger equation of wave mechanics was derived. The Schrodinger equation has many applications in the study of the behavior of small particles. In particular, it was used to explain the spectrum of atomic hydrogen more exactly than Bohr had been able to do without introducing the problems that Bohr had acknowledged with his model. Scientific achievements. In his research Schrodinger wanted to combine the Bohr atom model with de Broglie’s matter waves. In Schrodinger’s model, the electron can exist in one 14 Complete these activities. 1.46 Describe Schrodinger’s improvement on the Bohr model concept of orbits. _______________________________________________________________________________________ _______________________________________________________________________________________ 1.47 Describe de Broglie’s concept of the nature of matter. _____________________________________ _______________________________________________________________________________________ 1.48 De Broglie’s concept applies to matter under two specific conditions. Name the two conditions. a. ___________________________________________________________________________________ b. ___________________________________________________________________________________ 1.49 The Schrodinger equation describes the behavior of a particle in terms of another physical phenomenon. Name the other phenomenon. _____________________________________________ JAMES CHADWICK Scientific achievements. In 1931 Chadwick began the experiments that would result in the discovery of the neutron. Frederic and Irene JoliotCurie, daughter and son-in-law of Marie and Pierre Curie, had reported that when beryllium was bombarded with alpha particles, the resulting radiation from the beryllium caused protons to be emitted from paraffin wax, or from anything else that contained hydrogen. The kind of radiation produced was unknown, but Chadwick concluded that the alpha particles were ejecting neutral particles from beryllium nuclei of sufficient mass to cause protons to be emitted from the paraffin. Chadwick performed the Joliot-Curie experiments and analyzed the results using the Geiger counter, the high-pressure ionization chamber, and the expansion chamber. With these instruments he discovered the neutron in 1932. James Chadwick, English physicist, won the 1935 Nobel Prize in physics for his discovery of the neutron. He was born in Manchester, England, on October 20, 1891. Biographical details. Chadwick graduated from the University of Manchester and received his Master of Science degree there. He went to Germany on a scholarship to study under Hans Geiger. He was interned in Germany until the end of World War I. In 1919 Chadwick went to the Cavendish Laboratory to work with Rutherford. In 1923 he became assistant director of research at the laboratory and in 1935 he went to the University of Liverpool as professor of physics. During World War II Chadwick worked on the Manhattan Project in the United States. He returned to England in 1948 to become master of Gonville and Caius College at Cambridge University. Contribution to atomic science. The discovery of the neutron was of great importance since this particle was to be used several years later to initiate a chain reaction. Complete these activities. 1.50 Describe an alpha particle. _____________________________________________________________ _______________________________________________________________________________________ 1.51 Describe the effect alpha bombardment had on beryllium. ________________________________ _______________________________________________________________________________________ 1.52 Describe the result of firing a B-B at a bowling ball. ______________________________________ _______________________________________________________________________________________ 1.53 Describe the result of firing a bowling ball at a bowling ball. ______________________________ _______________________________________________________________________________________ 1.54 Draw a conclusion about the mass of a neutron if it is capable of displacing a proton. _______________________________________________________________________________________ 15 On the basis of what you have learned so far in this LIFEPAC, complete the following data table. Data Table 3 Particle 1.55 Electron 1.56 Proton 1.57 Neutron Charge Discoverer The atomic number of an element is defined as the number of positive charges in the nucleus. The mass number, or atomic mass, is the number of pro- Mass Number Atomic Number Year Discovered Mass Compared to a Proton. Location in Atom tons plus the number of neutrons in the nucleus. Atoms that have the same atomic number but different mass numbers are called isotopes. 14 7 15 7 N N Symbol of Element Complete these activities. 1.58 Use the preceding definitions to analyze nitrogen isotopes. a. What is the atomic number of the two isotopes? _______________ b. Why are they equal? _______________________________________________________________ 1.59 a. What are the mass numbers? ________ , ________ b. Why are they unequal? _____________________________________________________________ ___________________________________________________________________________________ 1.60 a. How many electrons does each isotope have? ________ ________ b. How do you know? _________________________________________________________________ ___________________________________________________________________________________ Adult check ___________________ Initial Date 16 17 1.76 1.77 1.78 1.79 1.74 1.75 1.71 1.72 1.73 1.70 1.69 1.64 1.65 1.66 1.67 1.68 1.62 1.63 1.61 1.80 The following crossword puzzle should help you review this section. 1 3 2 4 6 5 7 8 ACROSS 9 1. The particle of an atom with a negative charge. 6. Meaning identical to something else. 7. When you are on vacation in Florida, you are __________ a trip. 10 r 12 13 15 Symbol for phosphorus. 9. The element with an atomic number of 24. 10. A word meaning dimes, nickels, dollars. 11. Symbol for the element carbon. 12. A type of moss or soft coal. 13. Abbreviation for the number of protons in an atom. 15. Boy’s name. 17. Group of three singers. 19. Symbol of chromium. 21. A food similar to a sweet potato. 22. Element with an atomic mass of 80 and containing 45 neutrons. 23. Element with atomic number of 85. 25. A deceased leader of Red China. 26. Element with atomic mass of 39 and containing 20 neutrons. 27. All matter is composed of about 106 different kinds of these. 29. 14 16 17 19 8. 11 e 20 23 26 18 21 24 22 25 27 30 29 31 32 DOWN 1. To get free from something. 2. A proton has a _______ mass than an electron. The element making up the largest part of our bones and teeth (symbol) 3. A place to bury people. 4. Man’s name. 5. A penny = _______ cent. 9. Garment worn over the shoulders. 11. Formula for carbon monoxide. 13. Simplest particle of matter still having the properties of an element. 30. Dinosaurs lived a long time __________ . 31. Symbol for element with atomic number of 13. 14. Symbol for the element with 11 electrons. 16. Name of a popular breed of cat. Twenty-four inches is the same as two __________ . 18. Positively charged particle of similar mass to a neutron. 20. Symbol for radium. 22. Loud noise. 24. A drink which can be served warm like coffee. 25. A food from cattle. 29. Symbol for the element with 17 protons. 32. Adult check ___________________ Initial Date 18 Review the material in this section in preparation for the Self Test. The Self Test will check your mastery of this particular section. The items missed on this Self Test will indicate specific areas where restudy is needed for mastery. SELF TEST 1 Match these items. Each choice may be used more than once or not at all (each answer, 2 points). 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.010 1.011 1.012 1.013 1.014 1.015 1.016 1.017 1.018 1.019 1.020 _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ mass same as proton most of the mass of the atom postulated “open spaces” model negative charge discovered the proton father of atomic theory behavior of like charges mass 1/1837 that of one proton equal in number in an atom is emitted from a cathode-ray tube taught seven Nobel Prize winners discovered the electron positive charge outside the nucleus behavior of unlike charges postulated the quantum atom makes up the nucleus discovered the neutron neutral “raisin pudding” model a. b. c. d. e. f. g. h. i. j. k. l. protons protons and electrons protons and neutrons neutron electrons Chadwick J. J. Thomson Bohr Rutherford Dalton attract repel Write the letter for the correct answer on each line (each answer, 2 points). 108 1.021 The element ᎏ Ag has _____ protons. 47 a. 108 b. 47 c. 61 d. 107 e. 87 1.022 The man responsible for discovering the “open spaces” structure of the atom is _____ . a. Millikan d. Dalton b. Bohr e. Einstein c. Rutherford 1.023 A false statement concerning matter is _____ . a. matter cannot be subdivided b. matter is composed of many small particles called atoms c. matter is mostly empty space d. all matter contains mass e. matter is made up of about 100 different types of atoms 1.024 The true statement concerning the atomic nucleus is _____ . a. it takes up most of the volume of the atom b. it weighs approximately 10-20 grams c. it contains protons, neutrons, and electrons d. it contains most of the mass of the atom e. it is made up of electrons only 19 1.025 1.026 Carbon 14 has an atomic number of 6. Carbon a. 14 c. b. 6 d. 238 The element ᎏ U has _____ neutrons. 92 a. 92 d. b. 238 e. c. 330 has _____ electrons. 20 8 184 146 1.027 A symbol for an element _____ . a. may be used to represent a compound which contains the element b. is an abbreviation for the name of the element c. is used to represent 96,500 atoms of the element d. may be used to represent 22.4 liters of the element e. is of little use to chemists 1.028 The nucleus of an atom contains _____ . a. protons, neutrons, and electrons b. protons and neutrons, (except H) c. about half of the mass of the atom d. all of the electrons which are converted to atomic energy e. different types of particles, depending upon the particular element 1.029 Isotopes are described as follows: Isotopes _____ . a. are atoms of different elements which have the same mass b. of a given element have equal numbers of neutrons c. of a given element have very similar chemical properties d. of a given element have equal numbers of protons and neutrons e. are atoms that have gained or lost electrons 1.030 The atomic number of an atom is equivalent to the number of _____ . a. neutrons d. protons b. electrons e. protons and neutrons c. alpha particles 48 Score 60 Adult Check _______________ ___________________ Initial 20 Date