LEARNING GUIDE BASIC EDUCATION ASSISTANCE FOR MINDANAO Third Year Science Inside the Atom Structure of the Atom LEARNING GUIDE

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Third Year Science

Inside the Atom

Structure of the Atom

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Basic Education Assistance for Mindanao (BEAM) project. Prior approval must be

given by the author(s) or the BEAM Project Management Unit and the source must

be clearly acknowledged.

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Information about this Learning Guide

Recommended number of lessons for this Learning Guide: 2

Basic Education Curriculum Competencies

Third Year Science: Appreciate the contributions of early scientists in the

development of atomic theory.

• Recognize the significance of the contributions of early scientists in the development particularly the Laws of Conservation of mass, Definite Composition and Multiple Proportion

• Explain how radioactive elements are utilized in the diagnosis/treatment of diseases, the risks involved and the methods of protection

Objectives

• Describe the structure of an atom.

• Identify the particles in an atom.

• Explain an atomic theory and model studied by a scientist.

Essential concepts, knowledge and understandings targeted

• Matter is made up of very small particles (now called atoms) with a certain mass and size.

• Atoms of the same element have similar properties.

• Atoms contain negatively charged particles (now called electrons) which move about within an atom.These have very small mass-almost negligible.

• The atom has a dense, hard positively-charged center (now called nucleus).

• Electrons in atoms revolve around the nucleus in much the same way as planets revolve around the sun..

• Electrons occupy certain positions around the nucleus called energy "levels". The emission spectra of elements provide evidence for its existence.

• Atoms also contain neutral particles called neutrons.

• Electrons move about the nucleus in waves.

Specific vocabulary introduced

• Atom

• Electron

• Nucleus

• Proton

• Neutron

• Energy level

• Orbital

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Suggested organizational strategies

• Grouping students into small groups • Use of constructivist methods/strategies

Activities in this Learning Guide

Activity 1: Semantic Map

Multiple Intelligences

• Interpersonal

• Verbal/Linguistic

Skills

• Knowledge of dates events, places

• Observation and recall of information

Text Types

• Explanation

Activity 2: Use of Concept Cartoons

• Visual/Spatial

Skills

• Translate knowledge into new context • Understanding information

Text Types

• Narrative

• Explanation

Activity 3: Jigsaw

• Interpersonal

Skills

• Verify the value of evidence

• Knowledge of major ideas

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Text Types

• Narrative

• Explanation

• Discussion

Activity 4: Creating Models

• Interpersonal

• Visual/Spatial

Skills

• Understanding information

• Relate knowledge from several areas

Text Types

• Narrative

• Explanation

• Discussion

Activity 5: Building a model

• Interpersonal

• Visual/Spatial

• Verbal/Linguistic Skills

• Mastery of subject matter

• Grasp meaning

Text Types

• Narrative

• Explanation

• Exposition

• Discussion

Activity 6: Use of a Graphic organizer

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• Visual/Spatial

Skills

• Understanding information

• Mastery of subject matter

• Relate knowledge from several areas

Text Types

• Narrative • Explanation

• Discussion

Key Assessment Strategies

• Performance assessments

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Mind Map

The Mind Map displays the organization and relationship between the concepts and activities in this Learning Guide in a visual form. It is included to provide visual clues on the structure of the guide and to provide an opportunity for you, the teacher, to reorganize the guide to suit your particular context.

Stages of Learning

The following stages have been identified as optimal in this unit. It should be noted that the stages do not represent individual lessons. Rather, they are a series of stages over one or more lessons and indicate the suggested steps in the development of the targeted competencies and in the achievement of the stated objectives.

1. Activating Prior Learning

This stage aims to engage or focus the learners by asking them to call to mind what they know about the topic and connect it with their past learning. Activities could involve making personal connections.

Background or purpose

Atoms are the basic building blocks of matter. A chair, the air, even you are made up of atoms. As early as elementary grades, pupils have prior knowledge about atoms. This activity will help them relate their past knowledge to this lesson.

Strategy: Semantic map

The use of semantic map in activating students' prior knowledge is ideal for this lesson. It helps them to associate the word ATOMS to ideas that they understood in the past. The cue word (Atoms) will be written at the center of a piece of paper and all associations will be written around it.

Materials:

marking pen manila paper masking tape crayons

Activity 1 “Tell me about Atoms” (10 min)

• Divide the class into 7 groups of 6 to 7 persons. Let them choose a leader, a reporter, and a

recorder.

• Write the word ATOMS on the chalkboard, then ask the question:What words or ideas could you associate with this cue word ATOMS? You may illustrate or draw your ideas

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• Distribute the materials needed. Instruct them to write the cue word at the center of the manila paper then write the associations around it. When done, direct the groups to post their semantic maps on the chalkboard.

• Model the process of discussion by asking the question (for example): What is the reason why you associate the word PARTICLES with ATOMS?

• Remind students to be respectful of each other during their discussion, taking care not to embarrass or belittle classmates as they examine the written associations. Students may ask clarifications or elaboration of some items or ask examples. All inquiries are directed to fellow students.

Roundup

Affirm the very good participation of the groups. Ask the students to give a brief summary of their key ideas about the atom.

2. Setting the Context

This stage introduces the students to what will happen in the lessons. The teacher sets the objectives/expectations for the learning experience and an overview how the learning experience will fit into the larger scheme.

Background or purpose

Students should realize that scientists had varied views about the structure of atoms. It is enlightening and enriching to learn what matter is made up of by knowing the structure of atoms.

Strategy: Use of Concept Cartoons

Naylor and Keogh (1999), developed the Concept Cartoons as a teaching tool. It includes the use of visual images that are familiar to children and can stimulate starting points for investigations and offer challenges that may lead to structuring of ideas.

Material:

Teacher's Resource Sheet 1 What's Inside An Atom, page 15

Activity 2 What's Inside An Atom (10 min)

• Prepare 7 photocopies of Teacher's Resource Sheet 1 “What's Inside An Atom”, page 15 and draw the mind map on the board for the activity.

• Distribute the photocopied pictures to each group. Let them give their ideas about what is implied in the picture or what they can infer out of the picture. Accept whatever views they have. Do not make comments on their answers.

• Mention that even scientists had that varied views about the inside of an atom.

• Then post the enlarged mind map and explain the overview of the lesson. Emphasize that they will explore the views of different scientists about the atom in this lesson.

Roundup

Encourage students to participate actively in the activities.

3. Learning Activity Sequence

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Background or purpose

Students' background knowledge about atoms maybe insufficient and limited. A research about scientists and their studies about atoms could help them enrich that knowledge.

Strategy: Jigsaw

This strategy is a structure for small group work that encourages cooperative learning, group participation and group responsibilities. Students are formed into Home Groups ,then number themselves 1, 2, 3 and so forth according to the number of groups desired. The number of groups should correspond to the number of topics. All ones, twos, threes, and so forth will be regrouped respectively to comprise the Expert groups. Each expert group will be tasked to research on and study a particular topic. When finished, they will be asked to report about the topic to their Home Group.

Activity 3 The Experts at Work

Do the following tasks (grouping and doing research) 2 to 3 days before this activity:

• Form 6 groups of 6 to 7 members. members. This will be the “home” group. • Assign a particular number to each member in the group such as 1,2,3,..6.

• Regroup the members of the home group according to their numbers. That means, all

ones, all twos, all threes,etc., will be together. These will compose the “expert “ groups.

• Assign each expert group, to study the work of one of the following scientists who

have made studies about atoms . Expert Group 1 - John Dalton

Expert Group 2 - Sir Joseph John Thomson Expert Group 3 - Ernest Rutherford Expert Group 4 - Niels Bohr

Expert Group 5 - James Chadwick Expert Group 6 - Louis De Broglie

• Instruct each expert group to research on and study the significant discoveries about the

atom and also what Models they proposed about the ATOMS based there on.

(Note: The teacher should provide additional references for students' use, see Teacher's Resource Sheets 2 to 7 pages 16 to 22)

Home Group

1

2

3

1

2

3 Expert Group

Home Group

1

2

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• Tell the expert groups that each person in their group should have a specific role:

a. Team leader: This person is responsible for keeping the group focused and working on the task.

b. Record Keeper: He/she is responsible for keeping accurate records of the group's research activities, as well as the resources used.

c. Team Writer: This person is responsible for creating the presentation(note: all group members must contribute!) which each of the members will present to their home groups.

d. Team designer: He/she is responsible for designing the model and selecting materials to use in its creation.

• On the day of the activity, let them discuss among themselves the results of their research

work. Allow each expert group to finalize what they want to present. Give them 10 minutes to do this.

• Ensure that every member of the expert group has something to share when they go back to

their home groups.

• Instruct the expert groups to return to their home groups and report the information and

learning they had in their expert group. Allow 5 minutes for the reports/group sharing.

Formative Assessment

The accuracy of ideas presented and quality of participation in the home and expert grouping may be assessed.

Roundup

Compliment the efforts of students. Ask 1 or 2 volunteers from any of the home group to give a recount of each scientist's major contribution to the development of the present model of the atom. Summarize these with the whole class in a table similar to the one below.

SCIENTIST MAJOR CONTRIBUTION TO ATOMIC MODEL DALTON

THOMSON RUTHERFORD BOHR

CHADWICK DE BROGLIE

4. Check for Understanding of the topic or skill

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Background or purpose

Students should be checked whether they understood the lesson. In this stage, students will be made to create their own atomic model through an illustration or drawing, or a 3

dimensional model out of clay or any material they could think of.

Strategy:Creating Models

The models to be created by students will depend on their basic understanding of what they have read previously. The descriptions about these models will somehow point out whether students have understood the lesson.

Materials:

• manila paper

• marking pen

• masking tape

Activity 4 Create your Model (20 min)

• Assign the materials to be brought by each group.

• From the findings of the scientists in the previous stage of learning, tell students to create their own atomic model.

• Give students ample time to finish the task. When done, let them post their outputs, then start the reporting session. Their reports should tackle the following points which are significant in todays understanding of what atoms are made up of:

1. Matter is made up of very small particles(now called atoms) with a certain mass and size. 2. Atoms of the same element have similar properties.

3. Atoms contain negatively charged particles (now called electrons) which move about within an atom. These have very small mass- almost negligible.

4. The atom has a dense, hard positively-charged center(now called nucleus).

5. Electrons in atoms revolve around the nucleus in much the same way as planets revolve around the sun.

6. Electrons occupy certain positions around the nucleus called “energy levels”. The emission spectra of elements provide evidence for its existence.

7. Atoms also contain neutral particles called neutrons, in the nucleus. 8. Electrons move about the nucleus in waves.

Note to teacher: Atomic models can be found on the Teacher's Resource Sheets 12 starting on page 30.

• Give additional input about concepts not found in the reading materials or when misconception is observed. Include the following important points:

➢All matter is made up of atoms.

➢Atoms of the elements differ in the number of protons( example Hydrogen has 1, Helium

has 2, Lithium has 3, etc.)

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Formative Assessment

The quality of participation of the members can be a good gauge to assess them. The quality of the models and how closely they depict the results of the scientists' ideas may also be assessed.

Roundup

Ask these questions:

1. Based on the present atomic model, describe the nucleus of an atom. What are the particles found in it?

2. Describe where electrons are found in the atom and how they move. 3. Describe your model of the atom.

5. Practice and Application

In this stage, students consolidate their learning through independent or guided practice and transfer their learning to new or different situations.

Background or purpose

Students will be asked to apply what they learned by making a model. In this stage, they will make models using the concepts learned in atomic structure. The activity ion this stage will concretize what has been explained in the previous stage.

Strategy: Model-Building

Model-Building in this lesson, is a strategy where students will apply the knowledge of atomic model and subatomic particles to construct 3 dimensional models of some of the elements.

Materials :

modeling clay or play dough (to make play dough, see Teacher Resource Sheet 10, page 26) Periodic Table Of Elements (please refer to Teacher Resource Sheet 8 page 23)

Activity 5 Models of the Elements

1. Introduce the Periodic Table of the Elements. 2. Describe briefly how it was developed.(optional)

3. Discuss the information that may be obtained from the Periodic Table particularly the following:

• number of protons • number of electrons • number of neutrons

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4. Illustrate the atom of three elements by drawing a diagram showing the protons, neutrons and electrons.

5. Since the concept of energy levels and atomic orbitals has been taken up during the discussion about the Bohr model of the atom, the teacher may introduce the order of filling up of energy levels as an introduction to the lesson on electron configuration (see Teacher Resource Sheet 11 page 27)

6. Tell the students that their task is to build 3-dimensional models of five elements using modeling clay or play dough. Each group may be assigned to make a model of one element. The models must show the correct number of protons, neutrons and electrons for that particular element and their relative positions in the atom. 7. Demonstrate how this is done with the elements H,He or Li.

8. Remind the students to use the Periodic Table to obtain the needed information. Please refer to Teacher Resource Sheet 8 page 23.

9. They may use the table similar to the one below to organize the needed information. It contains some elements that you may like the students to use. Please refer to Student Activity Sheet 5 “Models Of The Elements” page 25.

Atomic No. Name No. of protons No. of neutrons No. of electrons

6 Carbon 6 6 6

7 Nitrogen 7 7 7

8 Oxygen 8 8 8

9 Fluorine 9 9 9

10 Neon 10 10 10

Formative Assessment

Assess the models constructed particularly the following:

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Roundup

Summarize the concepts learned at this stage by asking the following questions: 1. How do you obtain the following from the Periodic Table?

• No. of protons • No. of neutrons • No. of electrons

2. Elements are made up of the same subatomic particles, protons, electrons, neutrons. In what way do they differ?

6. Closure

This stage brings the series of lessons to a formal conclusion. Teachers may refocus the objectives and summarize the learning gained. Teachers can also foreshadow the next set of learning experiences and make the relevant links.

Background or purpose

To close the lesson, students will answer the activity entitled:”What's inside of Me.”This way, basic concepts about atomic structure will linger in their minds

Strategy: Use of a graphic organizer

Materials:

Student's Activity Sheet 6 “What's Inside Of Me”, page 28

Activity 6 “What's Inside Of Me" (20 min)

• Distribute the activity sheets entitled:What's Inside of Me to each group.

• Let them do the task at hand. When every group is finished, facilitate the reporting. Call one group to report one of the items.

• Provide necessary corrections when there are inaccurate answers. Clarify misconceptions and mis perceptions.

Formative Assessment

Participation in group activity can be assessed using a rubric.

Roundup

Mention that: We cannot see anything as small or smaller than atoms with our eyes, even with the electron microscope. Scientists study much smaller things without seeing them directly. These things are far beyond the range of sensory perception but not beyond human

understanding.

Teacher Evaluation

(To be completed by the teacher using this Teacher’s Guide) The ways I will evaluate the success of my teaching this unit are: 1.

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Teacher's Resource Sheet 1

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Teacher's Resource Sheet 2

John Dalton (1766-1844)

It was in the early 1800s that John Dalton, an observer of weather, discoverer of color blindness among other things, came up with his atomic theory. In the 1780's, Lavoisier ushered a new chemical era by making careful quantitative measurements which allowed the compositions of compounds to be determined with accuracy. By 1799 enough data had been accumulated for Proust to establish the Law of Constant Composition (Law of Definite Proportions). In 1803 Dalton noted that oxygen and carbon combined to make two

compounds. Each had its own particular weight ratio of oxygen to carbon (1.33:1 and 2.66:1),also, for the same amount of carbon, one had exactly twice as much oxygen as the other. This led him to propose the Law of Simple Multiple Proportions, later verified by Berzelius. In an attempt to explain how and why elements would combine with one another in fixed ratios and sometimes also in multiples of those ratios, Dalton formulated his atomic theory.

The ancient Greek philosophers had talked about atoms, but Dalton's theory was different in that it had the weight of careful chemical measurements behind it. It wasn't just a philosophical statement that there are atoms because there must be atoms. His atomic theory, stated that elements consisted of tiny particles called atoms. He said that the reason an element is pure is because all atoms of an element were identical and that in particular they had the same mass. He also said that the reason elements differed from one another was that atoms of each element were different from one another; in

particular, they had different masses. He also said that compounds consisted of atoms of different elements combined together. Compounds are pure substances (remember they cannot be separated into elements by phase changes) because the atoms of different elements are bonded to one another somehow, perhaps by hooks, and are not easily separated from one another. Compounds have constant composition because they contain a fixed ratio of atoms and each atom has its own characteristic weight, thus fixing the weight ratio of one element to the other. In addition he said that chemical reactions involved the rearrangement of combinations of those atoms.

Dalton's model says that atoms are tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were.

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Teacher's Resource Sheet 3

Joseph John Thomson (1856-1940)

One hundred years ago, amidst glowing glass tubes and the hum of electricity, the British physicist J.J. Thomson was venturing into the interior of the atom. He was investigating a long-standing puzzle known as "cathode rays." His experiments prompted him to make a bold proposal: these mysterious rays are streams of particles much smaller than atoms, they are in fact minuscule pieces of atoms. He called these particles "corpuscles," and suggested that they might make up all of the matter in atoms. It was startling to imagine a particle residing inside the atom--most people thought that the atom was indivisible, the most fundamental unit of matter.

Do atoms have parts? J.J. Thomson suggested that they do. He advanced the idea that cathode rays are really streams of very small pieces of atoms. Three experiments led him to this.:

In 1895 experiment by Jean Perrin, Thomson built a cathode ray tube ending in a pair of metal cylinders with a slit in them. These cylinders were in turn connected to an

electrometer, a device for catching and measuring electrical charge. Perrin had found that cathode rays deposited an electric charge. Thomson wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays. He found that when the rays entered the slit in the cylinders, the electrometer measured a large amount of negative charge. The electrometer did not register much electric charge if the rays were bent so they would not enter the slit. As Thomson saw it, the negative charge and the cathode rays must somehow be stuck together: you cannot separate the charge from the rays

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Thompson’s third experiment sought to determine the basic properties of the particles. Although he couldn't measure directly the mass or the electric charge of such a particle, he could measure how much the rays were bent by a magnetic field, and how much energy they carried. From this data he could calculate the ratio of the mass of a particle to its electric charge (m/e). He collected data using a variety of tubes and using different gases. The results were astounding. Just as Emil Wiechert had reported earlier that year, the mass-to-charge ratio for cathode rays turned out to be over one thousand times smaller than that of a charged hydrogen atom. Either the cathode rays carried an enormous charge (as compared with a charged atom), or else they were amazingly light relative to their charge.

Thomson's conclusions were bold: cathode rays were indeed made of particles which he called "corpuscles", and these corpuscles came from within the atoms of the electrodes themselves, meaning they were in fact divisible. Thomson imagined the atom as being made up of these corpuscles swarming in a sea of positive charge; this was his plum pudding model.

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Teacher's Resource Sheet 4

Ernest Rutherford (1871-1937)

Ernest Rutherford, physicist, who became a Nobel laureate for his pioneering work in nuclear physics and for his theory of the structure of the atom.

Rutherford was born on August 30, 1871, in Nelson, New Zealand, and was educated at the University of New Zealand and the University of Cambridge. Rutherford was one of the first and most important researchers in nuclear physics. Soon after the discovery of

radioactivity in 1896 by the French physicist Antoine Henri Becquerel, Rutherford identified the three main components of radiation and named them alpha, beta, and gamma rays. He also showed that alpha particles are helium nuclei. His study of radiation led to his formulation of a theory of atomic structure, which was the first to describe the atom as a dense nucleus about which electrons circulate in orbits .

In 1911, Ernest Rutherford performed an experiment to test the plum pudding model of the atom. He fired energetic a [He2+] particles at a foil, and measured the deflection of the particles as they came out the other side. From this he could deduce information about the structure of the foil. To understand how this works, imagine shooting a rifle at a mound of loose snow: one expects some bullets to emerge from the opposite side with a slight deflection and a bit of energy loss depending on how regularly the pile is packed. One can deduce something about the internal structure of the mound if we know the difference between the initial (before it hits the pile) and final (after it emerges from the pile) trajectories of the bullet. If the mound were made of loose, powdery snow, the bullets would be deflected very little; if the bullets were deflected wildly, we might guess that there was a brick of hard material inside.

Rutherford expected all of the particles to be deflected just a bit as they passed through the plum pudding. He found that most of the a’s he shot at the foil were not deflected at all. They passed through the foil and emerged undisturbed. Occasionally, however,

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Teacher's Resource Sheet 5

Niels Bohr (1885-1962)

The most important properties of atomic and molecular structure may be exemplified using a simplified picture of an atom that is called the Bohr Model. This model was

proposed by Niels Bohr in 1915; it is not completely correct, but it has many features that are approximately correct and it is sufficient for much of our discussion. The correct theory of the atom is called quantum mechanics; the Bohr Model is an approximation to quantum mechanics that has the virtue of being much simpler. (Here is a more realistic discussion of what atomic orbitals look like in quantum mechanics.)

The Bohr Model is probably familiar as the "planetary model" of the atom. It is used as a symbol for atomic energy (a bit of a misnomer, since the energy in "atomic energy" is actually the energy of the nucleus, rather than the entire atom). In the Bohr Model the neutrons and protons (symbolized by red and blue balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun (but the orbits are not confined to a plane as is approximately true in the Solar System). The adjacent image is not to scale since in the realistic case the radius of the nucleus is about 100,000 times smaller than the radius of the entire atom, and as far as we can tell electrons are point particles without a physical extent.

This similarity between a planetary model and the Bohr Model of the atom ultimately arises because the attractive gravitational force in a solar system and the attractive Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons in an atom are mathematically of the same form. (The form is the same, but the intrinsic strength of the Coulomb interaction is much larger than that of the

gravitational interaction; in addition, there are positive and negative electrical charges so the Coulomb interaction can be either attractive or repulsive, but gravitation is always attractive in our present Universe

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Teacher's Resource Sheet 6

James Chadwick (1891-1974)

James Chadwick was born in Cheshire, England on October 20, 1891, the son of John Joseph Chadwick and Anne Mary Knowles. .For four years, James Chadwick was a prisoner of war in Germany. When World War I ended, he returned to his native England to rejoin the mentor of his undergraduate days, Ernest Rutherford. Now head of Cambridge

University's nuclear physics lab, Rutherford oversaw Chadwick's PhD in 1921 and then made him assistant director of the lab.

Chadwick's own research focused on radioactivity. In 1919 Rutherford had discovered the proton, a positively charged particle within the atom's nucleus. But they and other researchers were finding that the proton did not seem to be the only particle in the nucleus.

As they studied atomic disintegration, they kept seeing that the atomic number (number of protons in the nucleus, equivalent to the positive charge of the atom) was less than the atomic mass (average mass of the atom). For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass. One leading explanation was that there were electrons and additional protons in the nucleus as well -- the protons still contributed their mass but their positive charge was canceled out by the negatively charged electrons. So in the helium example, there would be four protons and two electrons in the nucleus to yield a mass of 4 but a charge of only 2. Rutherford also put out the idea that there could be a particle with mass but no charge. He called it a neutron, and imagined it as a paired proton and electron. There was no evidence for any of these ideas.

Chadwick kept the problem in the back of his mind while working on other things.

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Teacher's Resource Sheet 7

Louis De Broglie (1892-1987)

He was born in Dieppe (Seine-Maritime), younger son of Victor, 5th duc de Broglie. Unlike his brother Maurice, who was primarily an experimental physicist, Louis de Broglie had the mind of a theoretician rather than that of an experimenter or engineer. His 1924 doctoral thesis, Recherches sur la théorie des quanta (Research on Quantum Theory), introduced his theory of electron waves. This included the wave-particle duality theory of matter, based on the work of Einstein and Planck. This research culminated in the de Broglie hypothesis stating that any moving particle or object had an associated wave. Louis de Broglie thus created a new field in physics, the mécanique ondulatoire, or wave

mechanics, uniting the physics of light and matter. For this he won the Nobel Prize in Physics in 1929. Among the applications of this work has been the development of electron microscopes to get much better image resolution than optical ones, because of shorter wavelengths of electrons compared with photons.

In his later career, Louis de Broglie worked to develop a causal explanation of wave mechanics, in opposition to the wholly probabilistic models which dominate quantum mechanical theory. Today, this explanation is known as the de Broglie-Bohm theory, since it was refined by David Bohm in the 1950s.

In addition to strictly scientific work, Louis de Broglie thought and wrote about the philosophy of science, including the value of modern scientific discoveries.

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THE PERIODIC TABLE OF THE ELEMENTS

6 C

12.0 Atomic Number

Symbol

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Teacher's Resource Sheet 9

The Periodic Table of Elements

The Periodic Table of Elements is an orderly arrangement of the elements

according to their atomic number such that Elements with similar physical and

chemical properties are in the same column.

The atomic number which identifies the element and differentiates it from other

elements corresponds to that element's number of protons. For a neutral atom, the

number of proton equals the number of electrons .

Another information which can be obtained from the Periodic Table is the relative

atomic mass of the elements. It is usually written on top of or below the element's

symbol. The relative atomic mass is an average value of the atomic masses and

relative concentrations of the isotopes of a particular element in a given sample.

That is why sometimes it is not a whole number.

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Student Activity Sheet 5

MODELS OF THE ELEMENTS

Objective:

To construct a 3 dimensional model of an element showing the number of protons,

electrons and neutrons.

Materials:

• Modeling clay or play dough

• Periodic Table of the Elements

• 1 m fine wire

Procedure:

1. Obtain the following information about the element assigned to your group from

the Periodic Table of the Elements:

• Number of protons

• Number of electrons

• Number of neutrons

2. Organize the data obtained in a table similar to the one below:

Atomic No.

Name

No. of protons

No. of neutrons

No. of electrons

3. Draw a diagram of the atom of the element showing the number of protons,

number of electrons and number of neutrons and their approximate locations.

4. Construct a 3-dimensional model of the element using modeling clay or play

dough based on the diagram.

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Teacher Resource Sheet 10

Making Play Dough

Materials:

3 cups flour

3 cups salt

3 tablespoons alum

Procedure

1. Combine ingredients and slowly add water, a little at a time.

2. Mix well with spoon.

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Teacher's Resource Sheet 11

ELECTRON DISTRIBUTION IN THE ENERGY LEVELS OF ATOMS

Niels Bohr, the Danish physicist who proposed the planetary model of the atom,

visualized the atom as composed of electrons circling the nucleus in much the same

way as the planets revolve around the sun.

Bohr further proposed that electrons do not possess the same energies but that the

energies they possess have certain specified values. That being so, they occupy

what he called energy levels (or shells) around the nucleus. Electrons with low

energies occupy energy levels close to the nucleus while those with higher energies

stay at energy levels further away.

The energy levels in an atom are numbered, starting with the lowest and closest to

the nucleus as 1, the next as 2, and so on. The maximum number of electrons that

can occupy a given energy level is determined by the formula:

Max no. of electrons = 2(n)

2

where n is the energy level number. For the first energy level (n=1), the maximum

electron population is 2(1)

2

_{= 2. For the second energy level (n=2), the maximum}

number of electrons is 2(2)

2

_{= 8 and for the third it is 2(3)}

2