Early Atomic Theory Homework Answers

Human understanding of atomic theory has developed vastly, thanks to the contributions of several scientists whose work spanned the early 1800s through the 1920s. The work of Dalton, Thomson, Rutherford, Bohr, and Schrödinger occurred over a short period, and their discoveries advanced atomic theory rapidly. Below is a brief summary of each of their contributions to atomic theory.

John Dalton

John Dalton was a scientist in the 1800s. Simply, he was the first to describe...

Human understanding of atomic theory has developed vastly, thanks to the contributions of several scientists whose work spanned the early 1800s through the 1920s. The work of Dalton, Thomson, Rutherford, Bohr, and Schrödinger occurred over a short period, and their discoveries advanced atomic theory rapidly. Below is a brief summary of each of their contributions to atomic theory.

John Dalton

John Dalton was a scientist in the 1800s. Simply, he was the first to describe atoms and their properties. His contribution to atomic theory consisted of five main tenets (1805): 

  • All matter is composed of small particles called atoms.
  • Atoms are the smallest unit of matter; Matter cannot be broken down into units smaller than atoms; Atoms are indestructible.
  • There are different kinds of atoms; atoms of the same kind of element are identical to each other. Atoms of the same element are identical in mass and size and have the same properties.
  • In chemical reactions, atoms are rearranged, combined, or separated.
  • Compounds are formed when two or more different kinds of atoms join together.

J.J. Thomson

J.J. Thomson was a scientist who lived from the mid 19th century until the mid-20th century. Around the turn of the century, he was the first to discover sub-atomic particles: he is credited with the discovery of the electron. Thomson's discovery led to related discoveries around isotopes and radioactivity.

Ernest Rutherford

Shortly after Thomson's discovery of the electron, Ernest Rutherford discovered a concentration of mass within the center of an atom, which he called the nucleus. His famous Gold Foil Experiment in 1909 showed that atoms were composed of a nucleus surrounded by electrons. His discovery added to atomic theory by describing the atom more accurately as a conglomerate of several subatomic particles.

Niels Bohr

Niels Bohr was an active scientist around the same period as Rutherford. They worked together on a model to describe the structure of the sub-atomic particles of an atom. The Rutherford-Bohr model, or simply the Bohr model (1913), describes the atom's structure as similar to a solar system. The nucleus is in the center and smaller particles such as electrons circularly orbit around it. Bohr's model is seen as a precursor to current quantum theory.

Erwin Schrödinger

Erwin Schrödinger created several equations that advanced the understanding of atomic theory on a quantum level. Early in his career, he described the movement of an electron as a wave-function. In quantum mechanics, Schrödinger's equation (1926) is a physics description that describes quantum behavior in relation to time. Schrödinger's description of atomic structure, the wave mechanical model, describes electron position within orbitals, not orbits. This conceptualization of atomic structure posits that electrons do not orbit in circles as Bohr suggested, but rather in a much more complex manner. Schrödinger's work was at the forefront of a sea change moment in scientific history when atomic understanding was advancing into the quantum realm.

Photo Credit: Clipart.com.

Purpose

To introduce students to the ancient theories of matter that led to the work of John Dalton.


Context

This lesson is the first of a five-part series that will broaden and enhance students’ understanding of the atom and the history of its discovery and development from ancient to modern times.

This lesson examines the ancient Greeks’ theories about the atom. The History of the Atom 2: Dalton explores early milestones in atomic theory and the role of John Dalton. The History of the Atom 3: The Periodic Table reviews the early development of the periodic table and its impact on atomic thought. The History of the Atom 4: J.J. Thomson analyzes the evolution of modern ideas on the inner workings of atoms and J.J. Thomson’s contributions. The History of the Atom 5: The Modern Theory investigates the development of modern atomic theory.

Greek philosophers Leucippus and Democritus first developed the concept of the atom in the 5th century B.C.E. However, since Aristotle and other prominent thinkers of the time strongly opposed their idea of the atom, their theory was overlooked and essentially buried until the 16th and 17th centuries. In time, Lavoisier’s groundbreaking 18th-century experiments accurately measured all substances involved in the burning process, proving that “when substances burn, there is no net gain or loss of weight.” Lavoisier established the science of modern chemistry, which gained greater acceptance because of the efforts of John Dalton, who modernized the ancient Greek ideas of element, atom, compound, and molecule; and provided a means of explaining chemical reactions in quantitative terms. (Science for All Americans, pp. 153–155.)

As this series of lessons explores further discoveries in the configuration, bonding, and inner structures of atoms, students will come to realize how much more refined, modernized, and scientific atomic theory has become since the critical breakthroughs of Lavoisier and Dalton three centuries ago.

It is important for students to understand that the study of matter continues to this day, and that humankind’s millenniums-old effort to identify, understand, and document the nature of matter eventually created modern sciences like chemistry and continues to lead to countless, purposeful technological advancements and inventions—like the TVs and computers that make the quality of life for humankind more and more fulfilling, convenient, and sometimes troubling. Students also should come to realize that, over time, the ancients’ ideas of matter were often proven inaccurate through modern science.

In middle school, students should have become familiar with the early theories of matter and how they led to the work of Lavoisier and the birth of modern chemistry. This awareness will help students better understand the importance of John Dalton’s work, and how he ultimately ushered in “the consistent use of language, scientific classification, and symbols in establishing the modern science of chemistry.” (Benchmarks for Science Literacy, pp. 250–251.)

Ideas in this lesson are also related to concepts found in these Common Core State Standards:

  • CCSS.ELA-Literacy.RST.9-10.1 Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
  • CCSS.ELA-Literacy.RST.9-10.2 Determine the central ideas or conclusions of a text; trace the text’s explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.
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Planning Ahead

This lesson should take two 45-minute class periods.

You may want to print out and make copies of these resources that students will read in the lesson if your students don't have access to computers with Internet access:

 


Motivation

Before students begin their Internet exploration into the history of the atom, review their present knowledge by asking questions like these:

  • What is matter?
    • (Matter is anything that has mass and occupies space.)
  • What is an atom?
    • (An atom is the smallest particle of an element.)
  • What is an element?
    • (An element is a substance that cannot be broken down into simpler substances under ordinary conditions.)
  • Why do you think it is important to study the history of the atom?
    • (Answers will vary. Accept any answers.)
  • In what ways do you think the study of matter has affected our lives?
      (Answers will vary. Accept any answers.)

As you discuss these ideas, be aware of common misconceptions that students may have. For example, students might consider matter to include “everything that exists is matter, including heat, light, and electricity.” They also might think that “matter does not include liquids and gases or that they are weightless materials.” Finally, they may consider the weight of matter as a “’felt weight’—something whose weight they can’t feel is considered to have no weight at all.” (Benchmarks for Science Literacy, pp. 336–337.) High-school students should be able to recognize these earlier misconceptions.

Activity—Time Travel: Greece, 5th century B.C.E.
As a way to pique students’ interest and focus the discussion, prompt students with the scenario below. Displaying an old map of Greece might enhance this experience.

“Imagine now, if you will, that you are able to travel back in time to the 5th century B.C.E. You find yourselves in ancient Greece in the presence of Leucippus and Democritus, the two philosophers credited with originating the concept of the atom. You have the privilege to observe the two men as they work on and discuss their ideas about the atom.”

Next, ask the following questions. It is not so important for students to come up with accurate answers as to try to comprehend the era, circumstances, and particulars that might have occurred when the atomic concept was first formed. Putting students in the sandals of the ancient Greeks also will help them better understand the bare-bones human thought process that was involved in developing these truly profound and otherwise unimaginable concepts.

Ask students:

  • What do you see? What are these men like?
  • Why are they talking about concepts?
  • What do you think their specific ideas are about the atom?
  • How do you think they have come to these conclusions? What tools, if any, are they using?
  • What is remarkable about what they are doing?

(Accept all answers, but ask students to offer explanations to support their views.)

The purpose of these exercises is to set up the lesson and establish students' level of awareness regarding the basic concepts and the critical early figures that first developed them.


Development

Class One 
Following this warm-up discussion, students should use their The Ancient Greeks student esheet to go to and read The Greek Concept of Atomos: The Indivisible Atom. This paper should serve as a good orientation about early Greek theories of the atom. As students read the specifics about Leucippus and Democritus, the five major points to their atomic concept, and the fate of their ideas until the 17thcentury, encourage them to take notes.

After students have read the article, ask them questions like these (listed on The Ancient Greeks student sheet):

  • How has modern civilization come to learn about the ideas of Leucippus and Democritus?
    • (Since nearly all of the original writings of Leucippus and Democritus were lost, the modern world has learned of their ideas through the writings of Epicurus and Lucretius. Aristotle’s vocal stand against their ideas also helped to suppress theories of the atom in his time.)
  • What are the five major points of their atomic theory?
    • (They are that (1) all matter is composed of atoms that are too small to be seen and cannot be split into further portions; (2) there is a void, which is empty space between atoms; (3) atoms are completely solid; (4) atoms are homogeneous, with no internal structure; and (5) atoms are different in their sizes, shapes, and weight.)
  • What is the significance of having a lower limit to which an atom can be divided?
    • (Having a finite, lower limit to which an atom can be divided establishes “a permanent foundation of ultimate particles with which to build up everything we see.”)
  • What is the purpose of a “void”?
    • (For atoms to change, motion is necessary. Motion is only made possible by a void or “a space entirely empty of matter through which atoms can move from place to place.”)
  • How do you think these philosophers were able to theorize to this level of specificity about the characteristics of the (invisible) atom and the laws of nature?
  • Why did their ideas “recede into the background” of atomic thought until the 17th century?
    • (Aristotle, a prominent philosopher of the time, disagreed with their concepts, as did the Catholic Church, which disagreed with the atomic notion that the universe was endless and “not created by any outside power” [God].)

While discussing the specific perspectives of each point, emphasize that modern science has proven the early Greeks to be incorrect about atoms having no inside voids (Point #3, Rutherford) or internal structure (Point #4, Thomson). The inaccurate notion that atomic theory laid buried between “Democritus to Dalton” also needs to be addressed, since its evolution and discovery can be credited to numerous important figures who added to its development in between.

Class Two
First, students should use their esheet to go to and read and take notes on The Atomists: Leucippus of Miletus and Democritus of Abdera. While discussing the material, include these questions:

  • What specific contributions did Leucippus and Democritus make in the development of their atomic theory?
    • (In basic terms, Leucippus first developed the theory of atoms and void, and Democritus expanded upon it.)
  • Why did Leucippus first develop the basic atomic theory in response to the Eleatics?
    • (He felt their theory about the universe being made up of the infinitely motionless mass called “the One” was inaccurate, since our senses tell us that motion occurs.)
  • How did the philosophers assess atoms in terms of the senses?
    • (They considered the senses to be “not completely reliable in what they report to the mind,” but that whether something is hot, cold, or of a certain color, these characteristics are, in the end, determined by “the type of atom and the quantity of void.”)
  • According to Democritus, how are universes formed?
    • (His theory suggests that atoms join and form a whirl or a vortex. Heavier materials then gravitate to the center of the vortex and form the earth. The lighter materials “go out to the edge of the vortex and eventually ignite due to the intense speed of its revolutions. These lighter atoms would then form the heavenly bodies.”)
  • How does modern atomic theory differ from the early Atomists?
    • (Modern theorists hold that “the atom is almost completely void with a very dense center, instead of the atom being completely solid without any void.”)

Students should come away from this reading with a better understanding of the separate contributions Leucippus and Democritus made in the development of their theory, the opposing theories of the Eleatics, the “basics” of their atomist theory, how the senses and universe were rationalized atomically, and how figures like Epicurus and Lucretius would later add to the development of the theory that still evolves today.

Next, students should read the third key reading of this lesson, Democritus of Abdera. As you examine his life and role in atomic theory, include these questions in your discussion:

  • What made Democritus “a man of great learning”?
    • (Democritus traveled extensively in search of knowledge and of learned men to engage. An expert geometer, Democritus also contributed to the advancements of mathematics, physics, ethics, and poetry.)
  • Was Leucippus the first to propose an atomic theory? Explain.
    • (No. Anaxagoras also came up with an atomic system, and atomic thought was said to date back to the early Pythagorean concept that “regular solids played a fundamental role in the makeup of the universe.”)
  • In what ways did Democritus advance and broaden the atomic theory?
    • (He made atomic theory a more “elaborate and systematic view of the physical world” than his predecessors. He “asserted that space, or the Void, had an equal right with reality, or Being, to be considered existent. He conceived of the Void as a vacuum, an infinite space in which moved an infinite number of atoms that made up Being [i.e., the physical world]. These atoms are eternal and invisible; absolutely small, so small that their size cannot be diminished . . . absolutely full and incompressible, as they are without pores and entirely fill the space they occupy; and homogeneous, differing only in shape, arrangement, position, and magnitude.”)
  • How was this significant?
    • (By establishing a basis for the physical world, he could describe how things—atoms—change, move, and are packed together. Further, he sought to explain “the whole of physics” and that the physical world could ultimately be explained in quantitative terms and is “subject to mathematical laws.”)
  • What was unusual about Democritus’ theory on the origin of the universe?
    • (It suggested that the world came about from the nature of atoms [necessity], and was not designed by some “supernatural being.”)
  • What is significant about Democritus’ wish to “remove the belief in gods”?
    • (He believed the gods were “only introduced to explain phenomena for which no scientific explanation was then available.” This kind of perspective suggests that there is an alternative, non-religious way of looking at and understanding the world: science.)

Assessment

Depending on your time availability, this assignment can be done in class and/or as homework.

It is important for students to understand the early theories of matter held by Leucippus and Democritus, including the views of those who opposed them, like the Eleatics and Aristotle. To make better sense of their readings and resources, students should create a chart in which they fill in characteristics of the various theories. They also should write a very brief analysis of how the theories are alike and how they differ. Their charts can serve as a very useful foundation as they head into the other lessons in this series.


Extensions

Follow this lesson with the other lessons in the history of the atom series: The History of the Atom 2: Dalton, The History of the Atom 3: The Periodic Table, The History of the Atom 4: J.J. Thomson, and The History of the Atom 5: The Modern Theory.


For a deeper understanding of the development of atomic theory and its figures, have students read Atomism, which details how early atomic theory fared over the centuries leading up to Galileo in the 1600s.


For greater insights and specifics on Aristotle’s agreement and opposition about the theories of Leucippus and Democritus, encourage students to examine The Atomists into Aristotle.


Students may also be interested in reading and reporting on in-depth biographies of Leucippus of Miletus and Aristotle.


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