Return to Chemistry IndexComposition of the Atom

Carol Zimmerman Lane Tech High School

2501 W. Addison St.

Chicago IL 60618

312-534-5400Objectives:

1. This lesson is for High School.

2. The students will become familiar with the following vocabulary:

atom proton neutron electron hadron

nucleus quark lepton probability wave

charge mass muon pion strong force

weak force vector boson gluon graviton Higg's boson

3. The students will be able to construct a model of the atom for any element.

A performance assessment will be made of this task.Materials Needed:Classbeaker water ethyl alcohol motor oil small pointed stick food coloring (optional) periodic table of the elementsGroup of foursheet of paper filled with circles gumdrops toothpicks calculatorIndividualsgumdrops toothpicks calculator wave lineStrategy:

Define the words: proton, electron, neutron, nucleus. Pass out copies of

the periodic table of the elements and put one enlarged element on the board or

the overhead. Review the recognition of the atomic number and atomic mass and

how one would use them to determine the number of protons, neutrons, and

electrons in the rest atom.

Have the class discuss perceptions of normal behavior of positively and

negatively charged particles. To demonstrate the effect of the strong force in

the nucleus: Fill a beaker half full of water. Float a layer of ethyl alcohol

on the top of the water. Add one or two drops of motor oil. It will remain

suspended between the water and the alcohol. (If you wish this to appear to be

magic, add the alcohol to the water out of the students' sight. If you want the

students to be aware of the two different layers, add a small amount of food

coloring to the water before adding the alcohol.) Poke at the oil bubble with

the stick and notice how it resists splitting. Relate this to the strong force

in the atom.

Pass out one sheet filled with circles to each group of four students.

Have each student in the group drop a pen or pencil, point down, from waist

height 25 times. The students will count the total number of marks that have

landed inside any of the circles. Using the ratio :

area of all of the circles_{=}dots inside any circlearea of the sheet of paper 100 dots Find the area of all of the circles. Divide this number by the total number of circles to find the area of one circle. i.e.area of all of the circles_{= area of one circle}number of circles Use the formula: A=pi*r^{2}

to find the radius and the diameter of one circle. Relate this to Rutherford's

experiments to find the size of the nucleus. Explain that to be completely

parallel there would be only one or two circles on the page, but that then you

would need at least 500 to 1000 drops of the pencil to get an adequate sampling.

Discuss electron orbits, including energy levels, probability theory, and

the formula for the maximum electrons in an orbit: 2n^{2}. Have each group

construct a model of a helium atom, using toothpicks and gumdrops. Color code

the atom, using a different color for protons, neutrons, and electrons.

Introduce wave theory. Explain that each element has a unique wavelength k

associated with it. Then for each energy level n, the circumference can be

found by the formula:

circumference = nk

Introduce modern physics by explaining that the word modern is extremely

relative. Any music more recent than the nineteenth century composers Verdi and

Wagner is considered modern. A turn-of-the-century Picasso painting is modern

art. In physics, nothing older than yesterday is classified as modern. Twenty

years ago scientists thought that an atom was composed of hadrons (protons,

neutrons, and pions), and leptons (electrons, neutrinos, and muons). Ten years

ago they were saying that hadrons were composed of quarks, of which there were

three different types. At this point you might bring up the origin of the word

quark. It was taken from the line "Three quarks for Muster Mark." from the

James Joyce novelFinnegan's Wake. In German there are two translations of the

word: the conventional "cottage pudding" and the colloquial "strange". By five

years ago the scientists recognized six kinds of quarks. The up, charm, and

truth (or top) each have a charge of +2/3. The down, strange, and beauty (or

bottom) each have a charge of -1/3. In addition, quarks have the "colors" of

red, blue, and green. Since quarks only exist in a high energy state, their

mass is actually greater than the rest mass of the hadrons they compose. In

addition to hadrons and leptons, atoms also contain vector bosons (the W and Z

particles and gluons) which are associated with the strong force which binds the

nucleus together, gravitons, and the Higg's boson.Performance Assessment:

Using their copy of the periodic table of the elements, gumdrops,

toothpicks, a model wave three wavelengths long, and a calculator, each student

will construct a correct model of the magnesium atom.Scoring Rubric:

BUILDING AN ATOMDemonstrated Competence6 -Exemplary ResponseThe numbers of protons, neutrons, and electrons are correct. The number of electrons in each orbit is correct. The circumference of each orbit is correct. There is appropriate scientific justification for all of the above. 5 -Correct ResponseThe numbers of protons, neutrons, and electrons are correct. The number of electrons in each orbit is correct. The circumference of each orbit may not be correct. There is no scientific justification for any of the above.Satisfactory Response4 -Almost Correct ResponseThe numbers of protons, neutrons, and electrons are correct. The number of electrons in each orbit is not correct and/or there is no mathematical explanation for that number. The circumference of each orbit is incorrect. 3 -Partial SolutionThe numbers of either the protons, neutrons, or electrons is incorrect. The other two are correct.Inadequate Response2 -Inadequate SolutionThe numbers for either the protons, neutrons, or electrons is correct. The other two are incorrect. 1 -Incorrect ResponseThe numbers of protons, neutrons, and electrons are all incorrect. 0 - The student leaves a blank page or writes "I don't know".