Date: 9/18-19/13

Subject/grade level: Chemistry 9-12

Materials: brown bag, construction paper, worksheets

Objective:

1. Define what atom is.2. Describe the structure of an atom 3. Explain how atomic theory is discovered by discussing experimental designs and

conclusions of famous scientists.

TEKS:

(6)  Science concepts. The student knows and understands the historical development of atomic theory. The student is expected to:

(A)  understand the experimental design and conclusions used in the development of modern atomic theory, including Dalton's Postulates, Thomson's discovery of electron properties, Rutherford's nuclear atom, and Bohr's nuclear atom;

(D)  use isotopic composition to calculate average atomic mass of an element

Engagement Give each group a brown lunch bag that contains different item. Ask students if they could figure a way of determining what’s inside. Discuss how scientists have used this indirect process to determine atomic structure (eg. Democritus).

>touch it, shake, smell, etc

>presentation can be accessed at http://prezi.com/8jqq4xgqt1gv/atomic-structure-and-theories/>4th century b.c., Democritus claimed that everything is made up of atoms (atamos-not cuttable).He reasoned that the solidness of the material corresponded to the shape of the atoms involved. Like how students did, he used analogies from senses, he gave an image of an atom that distinguished them from each other by their shape, size, and the arrangement of their parts

Exploration Students will be divided into group that consists of 3-4 students.

>5th class)25 students=4 students-5groups, 5students-1 group>2nd class) 28 students=4 studetns-2 groups, 5 students-4groups>role of students in each group; students will be given choice to decide what roles to take and will be asked to write them on their worksheet1,2)reader1,2; reads the passages out loud3)recorder; fill the worksheet

Each group will be assigned to a scientist.Each group will get print out that has some details on the scientist and history on how they discovered atomic structure. Then each group will make a poster on the scientist.Also, they will come up with 2 questions that rest of the class would have to answer after they listen to presentation.

4)material gatherer; collect materials such as construction paper5)leader; lead discussion to answer the wksts and to make a poster >list of scientists: Dalton (answers to questionnaire: BDACB)JJ Thompson (answers to questionnaire: CCDCB)Robert A. Milikan (answers to questionnaire: ACBAA) Rutherford (answers to questionnaire: CABAD) E. Goldstein (answers to questionnaire: CAABA) James Chadwick (answers to questionnaire:AABBA)>2A is a inclusion class and there are students who needs more help with reading material. James Chadwick worksheet would work best as it is bit shorter in length and assessing questions are easier than other papers.>for the print out that students will get, please look at attachments on page 3-14

Explanations Students will come up to the front of class and show their posters and explain what they have learnedTeacher summarizes what atom is and emphasize on relative size of atoms.

>smallest particle of an element that retains the properties of elementCopper=2.4*10^22 atomsearth=6*10^9 peoplemeaning ATOMS are SMALL>wkst for students to take note is attached at pg15

Elaborate Teacher will present wave model and Bohr’s model. Students will use what they have learned in class and compare all the different models that were discussed in class and fill a chart that summarizes them.

Following table in empty version is given to students to fill out.

Evaluate Collected questions that students worked in “exploration” section will be compiled and given as a quiz where they would have to work individually to answer the questions.

John Dalton (1766-1844)

My name is John Dalton. I am English chemist. You want to know something interesting other than my amazing chemistry discovery? Well. My brother and I was born color blind. So I studied and discovered some things about color blindness and people sometimes call it “Daltonism”.Now back to business…Yes, I’m the famous Dalton who came up with atomic theory. No one attempted to work on atom for about 2000 years since Democritus’ work. Anyway, I have recorded weather for 57 years and while doing that I discovered evaporated water exists in air as an independent gas. Then it made me wonder how water and air can occupy the same space at the same time when obviously solid bodies cannot.

Then, I had that light bulb moment and figured that if the water and air were composed of discrete particles, then evaporation might be viewed as a mixing of water particles with air particles. To test this theory, I performed series of experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixture as a whole. And in 1803, I ended up coming up with 4 postulates of atomic theory.

1) All matter is made of atoms. Atoms are indivisible and indestructible. In other words, Atoms cannot be created, destroyed, or transformed into other atoms in a chemical change. I based this hypothesis on the law of conservation of mass and on centuries of experimental evidence.2) Atoms of the same element are identical. The atoms of any one element are different from those of any other element.3) Atoms of different elements can physically mix together or can chemically combine with one another in simple whole number ratios to form compounds.4) A chemical reaction occurs when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of chemical reaction.

I mistakenly added another postulate when I first published this theory that said simplest compound of two elements must be binary, formed from atoms of each element in a 1:1 ratio. I had no experimental evidence to support this postulate, and it lead me to mistakenly assume that the formula of water was OH and the formula of ammonia was NH. As a result, atomic weights for oxygen and nitrogen were incorrect and my experimental data did not support many of the conclusions I drew from it.

1. Dalton suggested that atoms were indestructible and unchangeable to explain:a) why compounds combine in fixed weight ratios in chemical reactionsb) why mass is conserved in chemical reactionsc) why elements combine in fixed weight ratios to form compoundsd) why elements are characterized by the mass of their atoms

2. When elements react, their atoms combine in:a) Tripletsb) Pairsc) Arbitrary proportionsd) Simple whole number ratiose) 1:1 ratio

3. Dalton viewed chemical change as:a) Rearrangement of atomsb) Transfer of electronsc) A nuclear exchanged) Change of atoms from one type into anothere) Transfer of protonsf) Creation and destruction of atoms

4. Hydrogen combines with oxygen in a 1:8 weight ratio to form water. If every molecule of water contains two atoms of hydrogen and one atom of oxygen, an atom of oxygen must weigha) 1/8 times the mass of hydrogen atomb) 1/16 times the mass of a hydrogen atomc) 16times the mass of a hydrogen atomd) 8 times the mass of hydrogen atom

5. Dalton said that that elements are different distinguished from each other by:a) The shape of their atomsb) The weights of their atomsc) The charge on their ionsd) The density of their solid forms

J.J. Thomson (1856-1940)

Hello. My name is J.J. Thomson. I’m a British Physicist. I have been pretty smart since I was a boy. I entered college when I was 14 and received Nobel Prize in Physics in 1906. Even my son received Nobel Prize. Anyway, let me tell you about my work.Scientists worked with electricity long before they understood that current was made of electrons. The cathode tube was a prime example. The basic setup of cathode rays was to have two metal plates inside a glass tube. The air was removed from the glass container with a pump.

One plate (called the cathode) was connected to the negative side of an electrical supply and the other (called the anode) was connected to the positive side of the electrical supply. By switching on some voltage, scientists could make fluorescent streams of electricity travel from one end to the other end -- but no one knew how it worked. Some thought the rays were a wave traveling while others thought the rays were streams of particles.

In 1897, I decided to find out for sure. I placed cathode tubes in electric and magnetic fields. I knew that these fields will move particles from side to side, but won’t have much effect on how a wave moves. In my experiments, I found that rays are attracted to metal plates that have positive electrical charge. I knew that opposite charge attract and like charge repel, so I proposed that a cathode ray is a stream of tiny negatively charged particles and named it corpuscle. Later, people realized that electric current was in fact made of moving corpuscle and started calling them ELECTRON moving at high speed. I varied type of gas that I used in the tube and type of metal used

for electrodes and I found that cathode rays are not affected by them. So, I concluded that electrons must be parts of the atoms of all elements.

Based on what I have found about electron, I came up with Plum Pudding Model. You can imagine a plum pudding wherein the pudding itself is positively charged and the plums, dotting the dough, are the negatively charged electrons. As a whole, I strived to explain why most atoms were neutral.

1. How did J.J. Thomson know that the particles in the cathode-ray tube were negatively charged?a. The particles were spread evenly throughout the tube. b. Some of the particles went veering off at large angles to the tube. c. These particles were attracted to the positively charged anode, and he knew that opposite

charges attract each other. d. These particles were attracted to the negatively charged cathode, and he knew that like

charges attract each other.2. Why did Thomson include some positively-charged matter in his model of the atom?

a. He knew that positive charges existed within the atom because the cathode ray was attracted to a negatively charged surface.

b. If atoms contained only negative charges, the particles in the cathode ray would not be attracted toward the anode.

c. If atoms contained only negative charges, all matter would be negatively charged, and it is not. d. If atoms contained only electrons and empty space, then alpha particles should bounce right off

of them and never pass through.3. Which of the following best describes Thomson's model of the atom?

a. electron cloud b. solid ball the same throughout c. small ball within a large shell containing empty space d. ball of raisin-cookie dough with raisins representing electrons

4. How did J.J. Thomson know that the beam in the cathode-ray tube was not light? a. Light is not made up of particles. b. It could not be seen without a microscope. c. He used a magnet to bend the beam, and light cannot be bent by a magnet. d. The negatively charged particles in the beam were attracted to the negatively charged cathode.

5. The small, negatively charged particles discovered by J.J. Thomson are called __________ . a. protons b. electrons c. alpha particles d. neutrons

Robert A. Millikan (1868-1953)

My name is Robert A. Millikan. I’m American Scientist. I haven’t started off as a scientist though. I first worked as court reporter and then I studied Greek and Math at college. I got interested in elementary physics when I took a teaching post in 1891.

Let me tell you about the experiment that I carried out in 1909 to determine the size of the charge on an electron which earned me a Nobel Prize.

What I did was to put a charge on a tiny drop of oil, and measured how strong an applied electric field had to be in order to stop the oil drop from falling. By varying the charge on different drops, I noticed that the charge was always a multiple of -1.6 x 10 -19 C, the charge on a single electron. This meant that it was electrons carrying this unit charge. By combining known theories and my discover, I also determined the ratio of the charge to the mass which had relative mass of 1/1840 (actual mass=9.11*10^28g).

Here’s what my apparatus looked like and here’s what I did:

1. Oil drops were charged by friction and passed through a small hole in the upper plate2. A horizontal light beam illuminates the droplets3. Through the microscope, the droplets look like stars and the rate of fall can be determined4. An electric field was set up between the plates with a battery5. The drops move slowly upward

By adjusting the electric field upwards until the drop remains suspended in mid-air. At that instant for that drop, the electric force on it exactly matches the force of gravity that pulls drop downward. I found that drops with more electrons required higher voltage to stop.

1. What was the purpose of Millikan’s experiment?

a. To measure the elementary charge of an electron and demonstrate the quantized nature of the electronic charge

b. To measure the elementary charge of an protonc. To measure the size of electrond. To measure how fast oil drops

2. Milikan noticed that oil A requires 10 volts to stop while oil B takes 20 volts to stop from falling. Which oil contains more electron?

a. Both oils have same number of electronb. Oil Ac. Oil Bd. Oils don’t have any electron.

3. When high voltage was passed through the plate between chambers, oil drops moved upward instead of falling. What was the charge of the plate?

a. It’s not charged.b. Positivec. negative

4. What was the use of microscope part of apparatus?

a. To observe terminal speed of oil dropletsb. To observe initial speed of oil dropletsc. To put light into the apparatus

5. What is the direction of an electric field between the plates that holds a negatively charged droplet motionless?

a. Upwardsb. Downwardsc. To the leftd. To the right?

Ernest Rutherford (1871-1937)

My name is Enest Rutherford. I’m New-Zealand born physicist. I’m quite famous in atomic theory world. I even have an element named after me called Rutherfordium.

Even though there had been quite a few researches that studied atom but I felt that nature of the atom wasn’t well known enough. So I decided to aim a beam of alpha particles (helium nuclei containing two positive charges) at a sheet of gold foil surrounded by a fluorescent screen.

Because alpha particles have about 8000 times the mass of an electron and impacted the foil at very high velocities, it was clear that very strong forces were necessary to deflect and backscatter these particles. Rutherford explained this phenomenon with a revitalized model of the atom in which most of the mass was concentrated into a compact nucleus (holding all of the positive charge), with electrons occupying the bulk of the atom's space and orbiting the nucleus at a distance. With the atom being composed largely of empty space, it was then very easy to construct a scenario where most of the alpha particles passed through the foil, and only the ones that encountered a direct collision with a gold nucleus were deflected or scattered backwards.

In 1911, J.J. Thompson’s Plum Pudding model was accepted in chemistry field.

This model describes the atom consists of positive and negative charges that are

In 1911, J.J Thomson’s Plum Pudding model was widely accepted. This model states that atom consists of positive and negative charges that are spread evenly within the atom.

So I expected to find the most of the alpha particles to travel straight through the foil with little to no deviation.

To my great surprise, I found that most of the alpha particles passed straight through the foil but small percentage of them were deflected at very large angles and some were even backscattered.

1. In Rutherford's experiment, a thin gold foil was bombarded with alpha particles. According to Thomson's "plum-pudding" model of the atom, what should have happened?

a. All the alpha particles would have been deflected by the foil.b. All the alpha particles should have bounced straight back from the foil.c. Alpha particles should have passed through the foil with little or no deflection.d. Alpha particles should have become embedded in the foil.

2. alpha particle scattering experiment established that:

a. protons are not evenly distributed throughout an atom.b. electrons have a negative charge.c. electrons have a positive charge.d. atoms are made of protons, neutrons, and electrons.e. protons are 1840 times heavier than electrons.

3. What properties did Rutherford use in the design of the gold foil experiment?

a. alpha particle's negative charge and gold foil's positive charge b. alpha particle's positive charge and electron's negative charge c. positively charged electrons distributed in a uniform negative charge d. alpha particle's negative charge and random distribution of protons

4. Rutherford noticed that an alpha particle has twice the charge, but four times the mass of a hydrogen atom; that is there were two extra units of mass and no additional charge. What causes the extra mass?

a. neutrons b. quarks c. electrons d. heavier protons in alpha particles

5. Rutherford's alpha particle experiment with gold foil demonstrated the existence of what part of the atom?

e. neutrons f. electrons g. energy levels of electrons h. the nucleus

Eugen Goldstein (1850-1930)

My name is Eugen Goldstein. I’m German physicist.

Since the atom is electrically neutral, scientists figured that there must be positively charged particles present in the atom to neutralize the negative charges of the electrons. In 1886, I experimentally proved the existence of protons in the atom. I used a cathode ray tube. The basic setup of cathode ray tubes used in this experiment was to have two metal plates inside a glass tube. The air was removed from the glass container with a pump. One plate (called the cathode) was connected to the negative side of an electrical supply and it was perforated. The other (called the anode) was connected to the positive side of the electrical supply.

When high voltage was applied, rays were formed at the anode and when these rays strike the walls of perforated cathode, they produced a faint red light. Rays were traveling in the direction of cathode and I knew that opposite charges attract, so I concluded that rays were composed of positive particle, proton.

Proton is actually a hydrogen atom, which has lost its electron. Mass of proton is 1.6 x 10-24 gram which is 1840 times heavier than electron when you regard that mass of proton is 1. Proton is equal and opposite to the charge of electron, 1.6 x 10-19 coulomb.

1. How did Goldstein know that the particles in the cathode-ray tube were positively charged?a. The particles were spread evenly throughout the tube. b. Some of the particles went veering off at large angles to the tube. c. These particles were attracted to the negatively charged cathode, and he knew that opposite

charges attract each other. d. These particles were attracted to the positively charged anode, and he knew that like charges

attract each other.

2. The small, positively charged particles discovered by Goldstein are called __________ . a. protons b. electrons c. alpha particles d. neutrons

3. In the apparatus diagram, it doesn’t show what direction the electrons have moved. What direction did it move toward?a. Anodeb. Cathodec. Was evenly distributed throughout the tube

4. Why did Godstein make holes in the cathode?a. So that atoms wouldn’t break the tube by colliding into the wallsb. To see movement of protonsc. To see movements of electronsd. To see how neutrons move

5. Why was the experiment carried out in almost vacuum condition?a. To prevent other atoms in air from interfering with movement of protonsb. To speed up the particles movementc. To distribute protons evenly throughout the tube

James Chadwick (1891-1974)

My name is James Chadwick. I’m British scientist. I originally wanted to study mathematics as an undergraduate, but got in the wrong registration line, the line for physics, by mistake. Even though it was a mistake, I did so well in physics and I made this amazing discovery of atom’s structure called neutron and I got Nobel Prize in physics in 1935.

It is remarkable that the neutron was not discovered until 1932 when I used scattering data to calculate the mass of this neutral particle. Since the time of Rutherford it had been known that the atomic mass number of nuclei is a bit more than twice the atomic number for most atoms and that essentially all the mass of the atom is concentrated in the relatively tiny nucleus. As of about 1930 it was presumed that the fundamental particles were protons and electrons and so it confused scientists on why atomic mass of an element is not same as the mass of protons.

In 1930 it was discovered that Beryllium, when bombarded by alpha particles, emitted a very energetic stream of radiation. When a beam of this radiation hit a substance rich in protons, for example paraffin, protons were knocked loose which could be easily detected by a Geiger counter.

In 1932, I projected alpha particles toward Beryllium “ the light element”. I noticed that some particles were emitted after enduring the Beryllium target and some passed through paraffin wax. And so after much work and calculations I proved that the particles released from Beryllium were uncharged and had a mass slightly larger than protons (1.67*10^-24g). I concluded that those particle that didn’t pass through paraffin was neutron.

1. Rutherford noticed that an alpha particle has twice the charge, but four times the mass of a hydrogen atom; that is there were two extra units of mass and no additional charge. What causes the extra mass?

a. neutrons b. quarks c. electrons d. heavier protons in alpha particles

2. Which part of the atom did James Chadwick discover and prove?

a. Neutronsb. Protonsc. Electrons

3. Why was the particle that Chadwick found called neutron?

a. To honor the Chadwick, used his middle nameb. Because there was no net chargec. Because it was naturally made

4. In the experiment, what molecule did paraffin absorb?

a. Protonb. Neutronc. Electrond. None of the above

5. What does Geiger Counter count?

a. Protonb. Neutronc. Electrond. None of the above

Scientists Important Facts

Summary of Atomic ModelsIndivisible Electron Nucleus Orbit Electron Cloud

DemocritusDaltonThomsonRutherfordBohrWave