The Discovery of the Atom

12 Key excerpts on "The Discovery of the Atom"

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  General Chemistry: Atoms First

  • Young, William Vining, Roberta Day, Beatrice Botch(Authors)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  AlbertSmirnov/iStockphoto.com 2 Atoms and Elements Unit Outline 2.1 Development of Atomic Theory 2.2 Subatomic Particles and Atomic Structure 2.3 Atoms and Isotopes 2.4 Elements and the Periodic Table 2.5 The Mole and Molar Mass of Elements In This Unit… As we learned in Chemistry: Matter on the Atomic Scale (Unit 1), each of the 118 known elements is composed of a unique type of atom. In this unit, we describe the processes and discoveries that led scientists to understand the particles that compose atoms and the arrangement of those particles. We also discover that there are actually a number of dif-ferent variations, or isotopes, of the atoms associated with each element. We explore the structure of the atom in further detail and learn about the periodic table and the chemical counting unit, the mole. Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 Unit 2 Atoms and Elements 30 2.1 Development of Atomic Theory 2.1a Early Models and the Advent of Scientific Experimentation Chemists view nature in terms of our understanding of matter on the atomic scale, using models of very small, invisible objects to explain the properties of bulk-scale materials that we can see and measure. But when did the idea of atoms come about? How did we arrive at our current understanding? Start your exploration with Interactive Figure 2.1.1, a timeline of the development of modern atomic theory. Interactive Figure 2.1.1 Explore the development of modern atomic theory. (Aristotle’s 4 elements) W ave model Modern Dalton model 1803 Bohr model 1922 Thomson model 1897 Rutherford model 1912 Greek model Democritus 400 BC Timeline of atomic theory Modern understanding of the composition of matter started with the Greek philosophers. The Greek Philosophers and Alchemy The first ideas about the atom came from Greek philosophers between about 600 and 300 BCE.

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  Foundations of College Chemistry

  • Morris Hein, Susan Arena, Cary Willard(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  In chemistry we use models (theories) such as Dalton’s atomic model to explain the behavior of atoms, molecules, and compounds. Models are modified to explain new infor- mation. We frequently learn the most about a system when our models (theories) fail. That is the time when we must rethink our explanation and determine whether we need to modify our model or propose a new or different model to explain the behavior. 5.1 Dalton’s Model of the Atom Describe Dalton’s model of the atom and compare it to the earlier concepts of matter. The structure of matter has long intrigued and engaged us. The earliest models of the atom were developed by the ancient Greek philosophers. About 440 B.C. Empedocles stated that all matter was composed of four “elements”—earth, air, water, and fire. Dem- ocritus (about 470–370 B.C.) thought that all forms of matter were composed of tiny indivisible particles, which he called atoms, derived from the Greek word atomos, meaning “indivisible.” He held that atoms were in constant motion and that they combined with one another in various ways. This hypothesis was not based on scientific observations. Shortly thereafter, Aristotle (384–322 B.C.) opposed the theory of Democritus and instead endorsed and advanced the Empedoclean theory. So strong was the influence of Aristotle that his theory dominated the thinking of scientists and philosophers until the beginning of the seventeenth century. More than 2000 years after Democritus, the English schoolmaster John Dalton (1766–1844) revived the concept of atoms and proposed an atomic model based on facts and experimental evidence (FIGURE 5.1). His theory, described in a series of papers pub- lished from 1803 to 1810, rested on the idea of a different kind of atom for each element. The essence of Dalton’s atomic model may be summed up as follows: 1. Elements are composed of minute, indivisible particles called atoms. 2. Atoms of the same element are alike in mass and size.

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  From Atoms to Higgs Bosons

  Voyages in Quasi-Spacetime

  • Chary Rangacharyulu, Christopher J. A. Polachic, Chary Rangacharyulu, Christopher J. A. Polachic(Authors)
  • 2019(Publication Date)
  • Jenny Stanford Publishing

    (Publisher)

  Chapter 7

  When Is an Atom? 1

  Science has explained nothing; ...the more we know the more fantastic the world becomes and the profounder the surrounding darkness....

  —Alduous HuxleyAlong the Road: Notes and Essays of a Tourist (1925)

  7.1   The Classical Atom

  During the recent decades, it has become clear that there is no unique, objective physical characteristic that allows us to decide when we should and should not call an entity a fundamental particle ,2 except, perhaps, that the community of particle physicists agrees to do so. This has not always been the case and is, in fact, a recent development in the history of physics. The concept of a particle, whether fundamental or not, has dissolved over time as developments in physics have rendered the concept inherently ambiguous.

  Nearly 3000 years ago, natural philosophers conceived of the basic material of the physical world in terms of four or five fundamental elements. The candidates were earth, air, water, fire, wind, metal, wood, and quintessence 3 or aether . Which four or five elements were accepted by the community of philosophers or larger society was closely linked to many factors, including their cultural and religious beliefs, mythologies, understanding of physical processes, and geographical context. The microscopic structure of the elements required further consideration, and two competing views were commonly held: a plenary theory, in which matter contains no voids and can be divided into smaller pieces without end; and an atomic theory, in which the elements can be broken down only to a certain finite limit, where we encounter the fundamental pieces that form physical things: atoms .

  As discussed in the first chapter of this book, the Greek atomists are now remembered as the originators of this atomic theory, and Democritus is renowned as the chief expositor. A few characteristics of his atoms may be reviewed:

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  The Britannica Guide to the Atom

  • Britannica Educational Publishing, Erik Gregersen(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  CHAPTER 1 THE ATOM : DEVELOPMENT OF ATOMIC THEORY

  T he concept of the atom that Western scientists accepted in broad outline from the 1600s until about 1900 originated with Greek philosophers in the 5th century BCE . Their speculation about a hard, indivisible fundamental particle of nature was replaced slowly by a scientific theory supported by experiment and mathematical deduction. It was 2,000 years before modern physicists realized that the atom is indeed divisible and that it is not hard, solid, or immutable.

  WHAT IS AN ATOM?

  The atom is the smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry.

  Most of the atom is empty space. The rest consists of a positively charged nucleus of protons and neutrons surrounded by a cloud of negatively charged electrons. The nucleus is small and dense compared with the electrons, which are the lightest charged particles in nature. Electrons are attracted to any positive charge by their electric force. In an atom, electric forces bind the electrons to the nucleus.

  Because of the nature of quantum mechanics, no single image has been entirely satisfactory at visualizing the atom’s various characteristics, which thus forces physicists to use complementary pictures of the atom to explain different properties. In some respects, the electrons in an atom behave like particles orbiting the nucleus. In others, the electrons behave like waves frozen in position around the nucleus. Such wave patterns, called orbitals, describe the distribution of individual electrons. The behaviour of an atom is strongly influenced by these orbital properties, and its chemical properties are determined by orbital groupings known as shells. What follows in this chapter is a historical survey of the most influential concepts about the atom that have been formulated through the centuries.

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  Atomic Age America

  • Martin V. Melosi(Author)
  • 2016(Publication Date)
  • Routledge

    (Publisher)

  New discoveries and a shift away from the mechanistic perspective challenged atoms as indivisible and as the nominal particles of matter. Atoms would prove to be composites, functioning in much different ways than thought before. 39 The turning point came with the discovery of the electron. Like most other major discoveries, many scientists carried out the work that led to the electron over decades of painstaking effort, and, at times, with a little luck. Experiments in different areas of science, numerous debates, and theoretical speculations all contributed. A shift in emphasis from mechanics to electromagnetism was crucial, with the first concrete evidence of the interaction between electricity and magnetism in 1819–1820. The general research in electrical technology proved essential, and provided insight about the relationship between electricity and the atom. Vacuum discharges resulting in the identification of cathode rays was a promising line of inquiry leading to breakthroughs in subatomic particles. Researchers employed tubes as mini-chambers for such studies. Electric current was sent through gas in these devices, which themselves were placed between a strong magnet. Obtaining a vacuum, however, proved difficult. 40 Scholars claim that “modern physics” was born in November 1895 when German physicist Wilhelm Conrad Roentgen (1845–1923) discovered the x-ray. This event started the search for the inner structure of the atom, leading to a new scientific pathway and major revelations. But it also pointed to the way science was taking center stage in world events involving a growing community of researchers in several fields. 41 The momentous finding was not a lucky accident, as it could have been scripted in a melodramatic science-fiction movie. Working in his darkened laboratory with a cathode tube, Roentgen noticed that a paper screen coated with barium plantio-cyanide some distance away was glowing

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  College Physics

  • Paul Peter Urone, Roger Hinrichs(Authors)
  • 2012(Publication Date)
  • Openstax

    (Publisher)

  Most scientists were already convinced of the existence of atoms, but the accurate observation and analysis of Brownian motion was conclusive—it was the first truly direct evidence. A huge array of direct and indirect evidence for the existence of atoms now exists. For example, it has become possible to accelerate ions (much as electrons are accelerated in cathode-ray tubes) and to detect them individually as well as measure their masses (see More Applications of Magnetism for a discussion of mass spectrometers). Other devices that observe individual atoms, such as the scanning tunneling electron microscope, will be discussed elsewhere. (See Figure 30.3.) All of our understanding of the properties of matter is based on and consistent with the atom. The atom’s substructures, such as electron shells and the nucleus, are both interesting and important. The nucleus in turn has a substructure, as do the particles of which it is composed. These topics, and the question of whether there is a smallest basic structure to matter, will be explored in later parts of the text. Figure 30.3 Individual atoms can be detected with devices such as the scanning tunneling electron microscope that produced this image of individual gold atoms on a graphite substrate. (credit: Erwin Rossen, Eindhoven University of Technology, via Wikimedia Commons) 30.2 Discovery of the Parts of the Atom: Electrons and Nuclei Just as atoms are a substructure of matter, electrons and nuclei are substructures of the atom. The experiments that were used to discover electrons and nuclei reveal some of the basic properties of atoms and can be readily understood using ideas such as electrostatic and magnetic force, already covered in previous chapters. Chapter 30 | Atomic Physics 1181 Charges and Electromagnetic Forces In previous discussions, we have noted that positive charge is associated with nuclei and negative charge with electrons.

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  The Sciences

  An Integrated Approach

  • James Trefil, Robert M. Hazen(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  Because there was no place from which a parti- cle such as the electron could come other than inside the atom, homson’s discovery provided incontrovertible evidence for what people had suspected for a long time. Atoms are not the fundamental building blocks of matter, but rather are made up of things that are smaller and more fundamental still. Table 8-1 summarizes some of the important terms related to atoms. The Atomic Nucleus he most important discovery about the structure of the atom was made by New Zealand– born physicist Ernest Rutherford (1871–1937), a student of J. J. hompson, and his coworkers in Manchester, England, in 1911. he basic idea of the experiment is sketched in Figure 8-6. he experiment started with a piece of radioactive material—matter that sends out energetic particles (see Chapter 12). For our purposes, you can think of radioactive materials as sources of tiny subatomic “bullets.” he particular material that Rutherford used produced bullets that scientists had named alpha particles, which are thousands of times more massive than elec- trons. By arranging the apparatus as shown, Rutherford produced a stream of these subatomic bullets moving toward the right in the igure. In front of this stream, he placed a thin foil of gold. he experiment was designed to measure something about the way atoms were put together. At the time, people suspected that the small, negatively charged electrons were scat- tered around the entire atom, more or less like raisins in a bun. Rutherford was trying to shoot bullets into the “bun” to see what happened. What the experiment revealed was little short of astonishing. Almost all the subatomic bul- lets either passed right through the gold foil unafected or were scattered through very small angles. his result is easy to interpret: it means that most of the heavy alpha particles passed Drs.

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  Foundations of College Chemistry

  • Morris Hein, Susan Arena, Cary Willard(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  In chemistry we use models (theories) such as Dalton’s atomic model to explain the behavior of atoms, molecules, and compounds. Models are modified to explain new informa- tion. We frequently learn the most about a system when our models (theories) fail. That is the time when we must rethink our explanation and determine whether we need to modify our model or propose a new or different model to explain the behavior. CHECK YOUR UNDERSTANDING 5.1 Early Atomic Theory 5.2 Applying Dalton’s Model 1 5.3 Applying Dalton’s Model 2 5.4 Applying Dalton’s Model 3 FIGURE 5.1 (a) Dalton’s atoms were individual particles, the atoms of each element being alike in mass and size but different in mass and size from other elements; (b) and (c) Dalton’s atoms combine in specific ratios to form compounds. (a) (c) (b) O O O O O H H O H H O H O H O H H H H H H O H O H 5.1 Dalton’s Model of the Atom LEARNING OBJECTIVE: Describe Dalton’s model of the atom and compare it to the earlier concepts of matter. The structure of matter has long intrigued and engaged us. The earliest models of the atom were developed by the ancient Greek philosophers. About 440 b.c. Empedocles stated that all matter was composed of four “elements”—earth, air, water, and fire. Democritus (about 470–370 b.c.) thought that all forms of matter were composed of tiny indivisible particles, which he called atoms, derived from the Greek word atomos, meaning “indivisible.” He held that atoms were in constant motion and that they combined with one another in various ways. This hypothesis was not based on scientific observations. Shortly thereafter, Aristotle (384–322 b.c.) opposed the theory of Democritus and instead endorsed and advanced the Empedoclean theory. So strong was the influence of Aristotle that his theory dominated the thinking of sci- entists and philosophers until the beginning of the seventeenth century.

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  Science of Atoms and Molecules

  • (Author)
  • 2014(Publication Date)
  • Academic Studio

    (Publisher)

  Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties. ______________________________ WORLD TECHNOLOGIES ______________________________ History Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny quantities has been around for millennia, but these ideas were founded in abstract, philosophical reasoning rather than experimentation and empirical observation. The nature of atoms in philosophy varied considerably over time and between cultures and schools, and often had spiritual elements. Nevertheless, the basic idea of the atom was adopted by scientists thousands of years later because it elegantly explained new discoveries in the field of chemistry. References to the concept of atoms date back to ancient Greece and India. In India, the Ājīvika, Jain, and Cārvāka schools of atomism may date back to the 6th century BCE. The Nyaya and Vaisheshika schools later developed theories on how atoms combined into more complex objects. In the West, the references to atoms emerged in the 5th century BCE with Leucippus, whose student, Democritus, systematized his views. In approximately 450 BCE, Democritus coined the term átomos (Greek: ἄ τομος ), which means uncuttable or the smallest indivisible particle of matter. Although the Indian and Greek concepts of the atom were based purely on philosophy, modern science has retained the name coined by Democritus. Corpuscularianism is the postulate, expounded in the 13th-century by the alchemist Pseudo-Geber (Geber), sometimes identified with Paul of Taranto, that all physical bodies possess an inner and outer layer of minute particles or corpuscles.

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  Introductory Chemistry

  An Active Learning Approach

  • Mark Cracolice, Edward Peters, Mark Cracolice(Authors)
  • 2020(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 156 Chapter 5 Atomic Theory: The Nuclear Model of the Atom Dalton realized that the three laws could be explained if matter was made of atoms. Dalton’s atomic theory accounts for chemical reactions in this way: Before the reaction, the reacting substances contain a certain number of atoms of different elements. As the reaction proceeds, the atoms are rearranged to form the products. The atoms are neither created nor destroyed but are simply arranged differently. The starting arrangement is destroyed (reacting substances are destroyed in a chemical change), and a new arrangement is formed (new substances form). The main features of Dalton’s atomic theory are as follows (Figure 5.4): a summary of… Dalton’s Atomic Theory 1. Each element is made up of tiny, individual particles called atoms. 2. Atoms are indivisible; they cannot be created or destroyed. 3. All atoms of any one element are identical in every respect. 4. Atoms of one element are different from atoms of any other element. 5. Atoms of one element combine with atoms of other elements to form chemical compounds. As with many new ideas, Dalton’s theory was not immediately accepted. However, over time, an overwhelming quantity of evidence has accumulated to erase any doubt about the existence of atoms. Relatively recently, in 2013, scientists were able to capture the first images of atomic theory in action. Figure 5.5 shows a molecule with 26 carbon atoms and 14 hydrogen atoms undergoing a chemical change to become a different molecule composed of the same atoms. Figure 5.4 Atoms according to Dalton’s atomic theory.

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  Sciences

  • James Trefil, Robert M. Hazen(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  Nevertheless, Dalton and his contemporaries recognized that a few materials, called elements, could not be broken down into other substances by any chemical means. • Today we know that the myriad of materials around us is con- structed from smaller, more fundamental constituents called atoms, the chemical building blocks of our universe. These chemi- cal building blocks combine together to form all the materials in our universe, from simple elements like helium to incredibly com- plex organic molecules like proteins. In Chapter 11, you will see that the arrangement of atoms not only creates the diversity of matter, but also the myriad of properties that matter exhibits. SUMMARY • About 100 different elements are sufficient to form all the solids, liq- uids, and gases around us. Atoms, the building blocks of our chemi- cal world, combine into groups of two or more; these groups are called molecules. For thousands of years, atoms were discussed purely as hypothetical objects, but studies of Brownian motion early in the twentieth century and recent imaging of individual atoms in new kinds of microscopes have confirmed the existence of these tiny particles. Each atom contains a massive central nucleus made from posi- tively charged protons and electrically neutral neutrons. Surround- ing the nucleus are electrons, which are negatively charged particles that have only a small fraction of the mass of protons and neutrons. Early models of this kind of atom treated electrons like planets orbit- ing around the Sun. Those models were flawed, however, because each electron, constantly accelerating, would have to emit electro- magnetic radiation continuously. Niels Bohr proposed an alternative model in which electrons exist in various energy levels, much as you can stand on different levels of a flight of stairs. Electrons in the Bohr atom can shift to a higher-energy level by absorbing the energy of heat or light.

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  Introduction to General, Organic, and Biochemistry

  • Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
  • 2019(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  26 Atoms 2 CONTENTS 2.1 Composition of Matter 2.2 Classifying Matter 2.3 Postulates of Dalton’s Atomic Theory 2.4 Composition of Atoms 2.5 The Periodic Table 2.6 Arrangement of Electrons in an Atom 2.7 Electron Configuration and the Periodic Table 2.8 Periodic Properties 2.1 Composition of Matter In ancient Greece, two schools of thought tried to determine the compo-sition of matter. One group, led by a scholar named Democritus (about 460–370 BCE ), believed that all matter is made of very small particles— much too small to see. Democritus called these particles atoms (Greek atomos , meaning “not to cut”). Some of his followers developed the idea that there were different kinds of atoms, with different properties, and that the properties of the atoms caused ordinary matter to have the prop-erties we all know. Not all ancient thinkers, however, accepted this idea. A second group, led by Zeno of Elea (born about 450 BCE ), did not believe in atoms at all. They insisted that matter is infinitely divisible. If you took any ob-ject, such as a piece of wood or a crystal of table salt, you could cut it or otherwise divide it into two parts, divide each of these parts into two more parts, and continue the process forever. According to Zeno and his follow-ers, you would never reach a particle of matter that could no longer be divided. Today we know that Democritus was right and Zeno was wrong. Atoms are the basic units of matter. Of course, there is a great difference in the way we now look at this question. Today our ideas are based on evidence. Dem-ocritus had no evidence to prove that matter cannot be divided an infinite number of times, just as Zeno had no evidence to support his claim that mat-ter can be divided infinitely. Both claims were based not on evidence, but on visionary belief: one in unity, the other in diversity. In Section 2.3 we will Drs. Ali Yazdani & Daniel J. Hornbaker/Science Source Image of atoms by STM (scanning tunneling microscope).

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