TEKS 8.8 A AND BA Tiny Big Discovery!

TAKS Objective 3 – The student will demonstrate an understanding of the structures and properties of matter.

Learned Science Concepts:

Matter is composed of atoms.

Substances have chemical and physical properties.

Complex interactions occur between matter and energy.

TEKS Science Concepts 8.8The student knows that matter is composed of atoms. The student is expected to:

(A) describe the structure and parts of an atom; and

(B) identify the properties of an atom including mass and electrical charge.

OverviewAs this lesson is taught focus on the following concepts. An atom is very small and composed mostly of empty space. The proton is positively charged, located in the nucleus, contains most of the atom’s mass, and the number of protons identifies the element. The neutron’s mass is almost the same as a proton’s mass; it has no charge. The electron has almost no mass, is negatively charged, and is mostly likely located somewhere in a 3-dimensional configuration called an electron cloud.

Instructional StrategiesThese activities are built around models and visuals to help students construct understanding of particles that are not visible. Care must be taken when comparing the atom to a model so that misconceptions about the atom are not developed (See TAKS Objective 1 unit on Models). Students should understand that the atom is still a mystery.

The lesson titled Who Knew? helps students understand how scientists build knowledge from what previous scientists have discovered. This knowledge is based on the best information of the time.

Students will construct their understanding of atoms and atomic particles through the use of models and analogies. Beginning with a “black box” investigation, students will discover that scientific knowledge is sometimes dependent upon combining bits of information from many sources.

The activities are all centered on answering the question, “What is an atom?” Students will learn how scientists through history learned bits of information that were constructed into the model of the atom.

Lesson Objectives1. The learner will be able to describe the parts of an atom.

2. The learner will be able to compare mass and charges of the electron, proton, and neutron.

3. The learner will use appropriate models and analogies to describe the size of an atom and its particles.

4. The learner will explain how scientists are able to discover the properties of an atom.

For Teacher’s Eyes OnlyThe discovery and understanding of atoms has occurred over many centuries. Atoms are

so small that they cannot be seen using visible light which means they cannot be viewed

under a conventional microscope. Scientists find evidence and test their ideas to

discover what these small building blocks of matter called atoms are. If a scientist’s

idea holds up under much scrutiny and no contrary information negates the idea, then he

or she uses the idea to build new or enhance old theories.

Atoms are often perceived to be miniature solar systems with the nucleus in the center

and spheres of electrons orbiting in given paths around the center. This thinking has been

perpetuated by textbook diagrams of electrons orbiting in circular paths around a nucleus.

Such an electron would be constantly accelerating and thus giving off radiation. As the

electron emitted radiation, it would loose energy and fall toward the nucleus. The

frequency of radiation would increase (exactly opposite of a smaller orbital) and the atom

would collapse. Radiation emitted would be continuous rather than discrete spectrum.

This model does not hold up under any experiment.

In the early 1900s, Niels Bohr proposed a quantum mechanical model of the atom. The

Bohr Model assigned discrete orbiting paths for the single electron in the hydrogen atom.

The strength of this model is that it correctly predicted the major spectral lines

emitted and absorbed by the electron in the hydrogen atom. Quantum amounts of

energy are absorbed when an electron moves from the ground state to an excited state.

Likewise, quantum amounts of energy are emitted when the electron moves from an

excited state back to the ground state.

The weakness of the Bohr Model lies with the energy levels. There is no explanation

for the fine line spectrum that appears along with the strong spectral lines. The Bohr

model does not account for the existence of more than one electron, thus does not explain

the configuration of atoms other than the hydrogen atom. The model also fails to explain

molecular bonding. The Bohr model has some limited value, but is more inconsistent

than consistent with experimental information collected on atoms.

According to modern theories the atom can best be described mathematically.

Models and analogies can still be used, however, on a limited basis. Exact positions and

motions of subatomic particles cannot be measured and are thus unknown. An electron

orbital is a volume configuration that denotes where there is the probability of finding an

electron. These orbitals appear as fuzzy electron clouds.

Most of an atom is empty space. The nucleus, commonly composed of protons and

neutrons, is the massive part of the atom. A proton is about 1800 times as massive as an

electron. The electron does not have a size in the way that particles are thought of as

taking up space. Electrons occupy space according to a probability configuration

identified by the energy level. In other words, the first energy level is shaped like a solid

sphere. The second energy level looks like a dumbbell and so on. The electron is most

likely found somewhere inside this area, but not always. There is a small chance it could

be found elsewhere. Think of this example: During a school day, a second grade teacher

(s electron) is most like to be found somewhere in her classroom. She may also be found

in the hallway, playground, or even at home. The likelihood, however, is that she will be

found at various points in her classroom at different times of the day. The classroom is

her probability configuration. The principal (p electron) on the other hand has the whole

school as a probability configuration. A principal who spend most time roaming and

interacting is most like found somewhere within the school building during a normal

school day. The principal could even be found in the second grade teacher’s classroom.

Again, there is some possibility that the principal is found outside of the school, but that

is small.

The atom’s properties are for the most part determined by the nucleus or the

number of protons. Stripped of electrons, it is called a positive ion, but still is much like

the original atom. Electrons move randomly around like Bingo balls in a turning cage.

They can be shared between atoms or flowing freely as in electric current. Electrons have

a negative charge and are responsible for bonding in chemical reactions.

Atoms are too small to be seen with visible light. In the latter part of the 20th century,

the Scanning Tunneling Microscope (STM) was developed. The microscope has a

very sharp needle with one single atom at its tip. As the needle is passed over a surface, a

very small current is sent through the needle. The electrical field surrounding electron

clouds of an atom cause the current to increase and decrease as the needle gets farther or

closer to the electron cloud. The result is a three dimensional image that can be

constructed to show the shapes of the electron clouds.

Lesson Layout

Atoms

Engage

Explore

Explain

Elaborate

Cut it upSTM

Who Knew?

What and where is it?

The Atomic Field

Structure of an atom

Dramatization of an atom

Stripping electrons

Rap Song Poster

Student Misconceptions Misconception

Electrons are little spheres that orbit the nucleus of an atom.

Science ConceptElectrons have no known shape and almost no mass. They do not orbit. They are most probably found somewhere inside a defined shape, but could be anywhere outside it, too.

Rebuild ConceptUse analogies and compare an electron to a popcorn popper or Bingo cage. The electron could pop up at any spot or even pop out. Just like the popcorn and the Bingo ball, no two electrons can be in the same spot at the same time.

MisconceptionAtom’s are like miniature solar systems.

Science ConceptThe only thing an atom and a solar system have in common is both are mostly empty space.

Rebuild ConceptPerform a kinesthetic activity where students move around and act like the parts of an atom. They will get a “feel” of how unpredictable the motions of the atom’s parts are.

Misconception

The electron is about the same size as a proton or neutron.

Science ConceptThe electron has no size and practically no mass compared to the proton or neutron.

Rebuild ConceptCompare masses of the subatomic particles to known objects. For example: a proton is to an electron as an automobile is to a pound bag of chips. Size cannot be compared since the electron has no size.

Student Prior KnowledgeStudents should have some knowledge of what is meant by positive and negative charge. They should also know that empty space is void. Students should know that atoms are the smallest particles of matter.

5 E’s

ENGAGEActivity: Cut it Up

Class Time: 5 minutes

Materials:

One piece of 8 ½ by 11 inches paper per studentOne pair of scissors per students

Students will discover that an atom is small. More specifically, an atom is the smallest division of a material that still retains all of the characteristics of the material. Encourage students to cut a piece of notebook paper in half again and again always cutting in the same direction as many times as they can. Check out http://www.miamisci.org/af/sln/phantom/papercutting.html to see how many cuts to be the size of an atom. As students cut the paper into smaller and smaller strips, they will begin to have a kinesthetic understanding of how small an atom is. This lesson will help students understand the physical significance of size.

EXPLOREExploration 1

Activity: What and Where is it?

Class Time: 20 minutes

Objective: The learner will use appropriate models and analogies to describe the size of an atom and its particles.

Process Skills:

TEKS 8.2 (A) – The student is expected to plan and implement investigative procedures including asking questions, formulating testable hypothesis, and selecting and using equipment and technology,

TEKS 8.2 (B) – The student is expected to collect data by observing and measuring.

TEKS 8.2 (C) – The student is expected to organize, analyze, evaluate, make inferences, and predict trends from direct and indirect evidence.

Materials

Opaque boxes (shoe box) for each groupSolid objects to glue in each boxMarble

This activity is designed to get students thinking about how scientists describe things they cannot “see”. The activity is a spin-off of the Rutherford experiment to find the nucleus of an atom.

Build the Box Glue an object inside an opaque box. Insert a single marble into the box and seal the box. A different object can be used for each group.

Characterize the Object Present one of the boxes to the students and ask them what is in the box. Ask them how they could find out what is in the box without opening it. Give each group a box. Let them roll the marble around inside the box and try to determine the size, shape, and location of the object inside the box. The box can then be given to another group. See if the group’s results agree. This activity can be expounded upon or left as a short exercise.

Exploration 2

Activity: Who knew?

Class Time: 45 minutes

Objective: The learner will explain how scientists are able to discover the properties of an atom.

Process Skills:

TEKS 8.3 (B) – The student is expected to connect Grade 8 science concepts with the history of science and contributions of scientists.

Materials:

Poster boardMarking pensInternet

Procedure: This activity is designed to help students think and reason how scientists depend on their predecessors and build upon prior knowledge. Students may work individually or in groups of two to complete this activity. Assign the name of a scientist involved in atomic theory discoveries. A partial list is included in this procedure. Allow students to research their scientist and then draw a graphic representation of what they have learned on the poster board. Arrange the poster pictures in chronological order. Allow students to tell about their scientist. Discuss how each scientific discovery depended upon previous discoveries.

Scientist List:

Atoms were first suggested in 440 B.C. by Democritus, a famous Greek philosopher. He actually coined the term “atom” which came from the Greek word “atomos” meaning “indivisible.” Aristotle (384 – 322 B.C) was another Greek philosopher who followed Democritus but was much more popular and believed that all matter was composed of only four elements: earth, water, wind, and fire.

Society believed Aristotle and the idea of atoms did not come back on the scene until 1803 when an English school teacher named John Dalton introduced his idea of the atomic theory.

Dalton’s atomic theory contained three parts:

1. Everything is made up of atoms and the atoms cannot be created, divided, or destroyed.

2. Atoms of the same element are exactly alike while atoms of different elements are different.

3. Atoms join with other atoms to form new substances.

Dalton performed many experiments showing that compounds of different elements always combine in definite proportions. He believed this was because the elements were composed of individual atoms. His theory was revised as more was discovered about the atom.

The events that led to the development of the atomic theory as we know it today are as follows:

440 B.C. Democritus coined the term “atom”

1803 John Dalton proposed that all atoms of a substance are alike and that they can join other atoms to form a new substance.

1897 J.J. Thomson conducted a famous experiment with a cathode ray tube. He shot an electric current through a tube that had a negatively charged plate attached to the top and a positively charged plate attached to the bottom. When the plates were not charged, the beam went straight through the tube and made a small glowing spot at the end of the tube. When the plates were charged, the glowing spot was considerable lower, showing that the beam was bending toward the positively charged plate. This showed that the beam must contain negative particles because it was attracted to the positively charged plate. From this experiment he came up with the “plum pudding” model of the atom. He proposed that the atom was like plum pudding in that it was mostly a positive material (the pudding) with negative particles scattered throughout (the plums).

1869 Dmitri Mendeleev arranged elements into seven groups according to their atomic weights. Each group had similar chemical properties. He predicted that there were still unknown elements.

1898 Ernest Rutherford studied the radioactive decay of uranium and thorium. He named the particles alpha and beta. Later it was discovered the alpha particles were helium nuclei and beta particles were electrons.

1903 Hantaro Nagaoka proposed a model of the atom. This model resembled Saturn with flat rings of negative particles circling the positive particle.

1909 Ernest Rutherford conducted his famous gold foil experiment. He bombarded a thing piece of gold foil with alpha particles (+) and deducted that atoms

are mostly empty space. The beam went straight through the foil as if it were not there most of the time rather than being continuously deflected. Once in a while, it would bounce back with great force showing that the center of the atom must be positive and massive because + repels +.

1913 Neils Bohr suggested that electrons travel around the nucleus in definite paths and that they could jump from a path in one level to a path in another level. His model became known as the planetary model.

1914 H.G.J. Moseley used cathode rays to bombard atoms. He photographed the resulting x-rays. Using the information he interpreted from the photographic plates, he was able to determine the positive charge on the nucleus of the atom. From this he was able to reorganize the Periodic Table.

1919 Francis William Aston developed the mass spectrograph, a device that separates atoms or molecular fragments of different mass and measures those masses with remarkable accuracy.

1924 Louis de Broglie proposed that matter has wave properties.

1926 Erwin Schrödinger developed wave mechanics to describe the behaviors of quantum systems of subatomic particles.

1027 Werner Heisenberg formulated the uncertainty principle that states the position and speed of a subatomic particle cannot both be determined exactly.

1932 James Chadwick discovered neutrons.

EXPLAINShow the video “The Atomic Field” narrated by Dr. Sam Matteson. The video will provide students with a vivid picture analogy of the comparative sizes of subatomic particles and space. Let students discuss the idea of an atom being mostly empty space.

Show the PowerPoint of the structure of an atom. The animated graphics representing the atom will show its structure and some idea about the position of the particles including the unpredictable path of the electron.

Discuss with students the limitations of models. In the case of the model of the atom it does not adequately show the relative sizes and masses. It also depicts the subatomic particles at small hard spheres which is not accurate. Without drawing any conclusions, allow students to speculate why we use models and what might be some good models for the atom.

STM Question - How can you know about something that is smaller than light? After discussion, show the PowerPoint animation of an atom photo taken with the Scanning Tunneling Microscope at the University of North Texas. Animation Students often think that scientists can see and easily measure things they study. Start students thinking about how things that cannot be seen or touched can still be measured. The ideas of how scientists “know” and why they think certain things are concepts that should run through all aspects of every science lesson.

ELABORATEElaboration 1

Role play: Particle Play

Class Time: 10 minutes

Objective: The learner will be able to describe the parts of an atom.

Materials

Cards attached to a string that hangs about the necks of each student

Preparation Divide the class into thirds with one third being electrons, one third protons, and the rest of the students being neutrons. Prepare cards that say “proton”, cards that say “neutron” and cards that say “electron”. The proton cards should have positive signs on the back (). The electron cards should have negative signs on the back (). The neutron cards should have null signs on the back ().

Play Protons and neutrons should stay close together. Protons should push on each other but never get more than an arm-length apart. Electrons should move randomly around the nucleus trying to get close to the protons while staying away from each other.

Elaboration 2

Activity: Stripping Electrons

Class Time: 20 minutes

Objective: The learner will be able to describe the parts of an atom.

Materials

Aluminum pie plateStyrofoam cupStyrofoam plateSandwich bagTape

This activity will help students understand that electrons can be easily removed from the atom without changing the original material. The students will also be able to confirm that electrons have a charge by creating a spark. Students will strip electrons using friction and collect the charge on an aluminum pie pan.

5. Attach the Styrofoam cup upside-down to the aluminum pie pan.

6. Put the sandwich bag on like a glove and use it to rub the Styrofoam plate, or rub the bottom of the Styrofoam plate on the carpet.

7. Place the pie pan on the rubbed surface of the Styrofoam plate. Use the cup to hold the pie pan, do not touch it. (Styrofoam plate on top, pie plate, cup on bottom).

8. Perform this act several times.

9. Holding the pie pan by the cup, very slowly touch the edge of the pan to your nose or earlobe. Electrons will fly!

(Note: if there is a lot of humidity, this may not have a very pronounced effect. You might try rubbing the Styrofoam plate on carpeting or hair and then transfer to the metal pie pan. You might also get a larger spark if you leave the Styrofoam plate in contact with the metal pie pan when you touch it. As a backup (if all else fails), tape two pieces of cellophane tape to the desk; Rip both up quickly and they will repel or attract each other depending on which side is introduced.)

Styrofoam cup handle andPie pan

Styrofoam plate

Elaboration 3

Activity: On the shoulders of giants

Objective: The learner will explain how scientists are able to discover the properties of an atom.

The students may form groups and choose a project that demonstrates the development of the atomic theory. They may:

Compose a song, poem, or rap. Make a poster. Act out a dramatization. Other – student choice.

EVALUATEAllow students to choose a particle and write its “biography”. Include its discovery, charge, position in the atom and other information. For some students it may be more effective to allow them to draw a pictorial story of the particle with verbal or written comments.

Making Models of Atoms

Create models of each of the following atoms using the information in the periodic table boxes. After you finish, have your teacher check your work, then copy the model onto this page. Make sure your subatomic particles match the key.

K E Y

Proton = Neutron = Electron =

1H

1.008Hydrogen

2He

4.0026Helium

3Li

6.941Lithium

+

4Be

9.012Beryllium

5B

10.81Boron

6C

12.011Carbon

7N

14.007Nitrogen

8O

15.999Oxygen

9F

18.998Fluorine

10Ne

20.179Neon

Quiz – The Atom and its Subatomic Particles

Choose the letter of the answer choice best described by each statement. Each answer choice may be used once, more than once, or not at all.

1. ______ This subatomic particle has a neutral (0) charge.

a. proton

b. neutron

c. electron

d. nucleus

e. electron cloud

f. +1

g. 0

h. -1

2. ______ This subatomic particle has a charge that would repel an electron.

3. ______ This subatomic particle moves randomly about the atom.

4. ______ An atom with three protons and two electrons has this overall charge.

5. ______ This positively charged subatomic particle is always found in the nucleus.

6. ______ Other than the answer to question 5, this is the only subatomic particle always found in the nucleus.

7. ______ The negatively charged subatomic particles are found in this.

8. ______ The number of this subatomic particle determines the identity of the atom.

9. ______ This subatomic particle has a charge that attracts an electron.

10. _____ This is the region of the atom where almost all of the atoms mass is located.