11 April 2000: Marva Anyanwu (Green School)
gave us some peanut M&Ms and chocolate M&Ms and a handout dealing with isotopes and atomic mass. We first sorted the M&Ms of both kinds into piles by color. Then we assigned a mass of 4 to each red peanut and 1 for each red chocolate. The red corresponds to a certain element or atom, while the peanut and chocolate varieties represent different isotopes of that red atom.

If we have, say, 2 peanut and 2 chocolate red M&Ms in a pile together, then the atomic mass of that mixture of peanut and chocolate "isotopes" of the red "atoms" will be (2x4 + 2x1)/4 = 10/4 = 2.5. We proceeded on to green M&Ms, with the peanut variety of green having a mass of 4 and the chocolate a mass of 3. If we had a mixture of 2 of each of those "isotopes" of the green "atoms" the atomic mass would be (2x4 + 2x3)/4 = 14/4 = 3.5; so students will come to understand why atomic masses don't come out as integers for a mixture of different isotopes of the same kind of atom. A nicely drawn analogy which clarifies the concept of atomic mass. Quite pretty!

23 January 2001: Pat Riley (Lincoln Park HS)
started out by asking what was inside an atom.  After drawing a model of the atom, she stated that protons and neutrons lie inside the nucleus, a tiny, heavy core.  We then went on to explore the functions of the protons and neutrons.

Protons, being positively charged, attract the negatively charged electrons, which move in orbits around the nucleus. Neutrons serve as a kind of nuclear glue to keep the nucleus together, in spite of the "like charged" repulsion of the protons.  These electron orbits may classified according to various orbital shells, which lie further and further from the nucleus, and which may contain more and more electrons.  In the Bohr model, here are the orbits and the various numbers of electrons that they may contain.

The negatively charged electrons move in one of  these orbits and stay close to the nucleus because of the attraction of the positively charged protons.

Pat then went on to tell us that this simple Bohr model is actually too simple!  She made an analogy of these orbitals with the rooms on various floors of a hotel.  These rooms may be of these types:

circular [S-orbitals]
figure-8 [P-orbitals]
4 petaled (daisy-shaped) [D-orbitals]
            ...   and even   ...
6-petaled [F-orbitals].

 

Orbital Number	Floor Number	Number of Orbitals / Rooms	Number of Each Type
n = 1	First Floor	1	1:  circular S-orbitals
n = 2	Second Floor	4	1:  circular S-orbitals 3:  figure-8 P-orbitals
n = 3	Third Floor	9	1:  circular S-orbitals 3:  figure-8 P-orbitals 5:  4-petaled D-orbitals
n = 4 ...	Fourth Floor	16	1:  circular S-orbitals 3:  figure-8 P-orbitals 5: 4-petaled D-orbitals 7: 6-petaled F-orbitals

We should think of the rooms as three dimensional---spherical rather than circular, dumb-bell shaped rather than figure-8, and so forth.

Pat showed how that this model allows us to understand how electrons are packed into the small amount of space around the nucleus.  Also, she pointed out that it is difficult to visualize electrons, since

[1] the electrons themselves are very small, if not "point particles";
but
[2] the electronic orbitals take up 99.999999... percent of the space inside the atom.

05 December 2000: Terry Donatello (St. Edwards)
asked this question

"How do you look at the properties of materials and relate them to the Periodic Table?

She had us pair up and then handed out a deck of specially prepared cards to each pair. The cards were all the same shape and size, and were yellow, green or gray in color. They were numbered 1 through 20, but the numbers were drawn with several different types of markers or pens. How could the cards be organized into some sort of order or pattern? Perhaps first according to the number on the card, or card color, or type of marker or pen marks. For example, they might be ordered first by number (1- 20) in several rows. Then the rows ordered in columns by color, say gray under gray, green under green, yellow under yellow. By doing this, we simulate an arrangement like the periodic table. Interesting analogy!

Next, Terry showed us the shapes of magnetic fields by sprinkling iron filings on paper, then holding a bar magnet underneath. The filings form a pattern outlining the shape of the magnetic field or "lines of force." But what does the pattern look like for different magnet shapes? Terry tried round magnets (disks), a horseshoe magnet, and refrigerator magnets. So we started to investigate the correlation between magnet shape and magnetic field geometry as shown by the pattern of iron filings. Different shaped magnets produced different shaped fields. All, however, had field "lines" connecting one pole of a magnet to its other pole. A beautiful way to lay a concrete basis for the ideas of magnetic fields and lines of force. Thanks, Terry!

01 May 2001: Karlene Joseph (Lane Tech HS) Handout: Radioactive Decay
The half-life of a radioactive element is defined as the time required for half of the atoms in question to decay.  For example, the unstable isotope Carbon 14 decays into the stable isotope Carbon 12 with a half-life of 5500 years.  [This feature is used for "carbon dating" of wood and wood products, since the fraction of Carbon 14 in the earth's atmosphere is being kept roughly constant by background cosmic rays.]  We modeled radioactive decay using red licorice [unstable, radioactive] and black licorice [stable], made by Twizzlers™.  We took a full piece of the red licorice, and cut another one successively in halves, which we glued to the paper to indicate the number of atoms present after various half-lives.  The graph looked something like this:

        Number Left
          |
          |
          | 
          |
          |     | 
          |     |
          |     |     |
          |_____|_____|_____|_____.
          
          0     1     2     3     4

         Time:  Half-lives 

     |: Number Left       X: Number New
          |     X     X     X     X
          |     X     X     X     X
          |     X     X     X     X
          |     X     X     X     X
          |     |     X     X     X
          |     |     X     X     X
          |     |     |     X     X
          |_____|_____|_____|_____X
          
          0     1     2     3     4

         Time:  Half-lives 

07 May 2002: Christine Etapa (Gunsaulus Academy) -- Teaching Atoms
Chris divided the lesson into these three parts:

1. First, Chris described a recent exercise with students in her class:
   She took the class to the school yard, and some played the role of protons or of neutrons.  These two groups were tightly huddled to form a central nucleus, with protons rotating clockwise and neutrons rotating counterclockwise to distinguish one type of particle from another. Other students (representing electrons) moved in circular orbital paths about the nucleus. The inner circles represented the lower energy levels, whereas outer circles represented higher energy levels.  Altogether this is a model for one atom. As an extension of this lesson, one could use the "student mass aggregate" to model two atoms, which then could form a compound by sharing valence electrons with one another, either through "time sharing" [covalent bonding] or by "leave of absence" [ionic bonding].
   
2. Next, Chris had us form the Helium⁴ atom, which consists of 2 protons and 2 neutrons in the nucleus, and 2 electrons lying in the same circular track about the nucleus. Then we modeled the [highly unstable isotope of a cumulatively toxic semi-metallic element] Beryllium⁸ atom, with 4 protons, 4 neutrons, and 4 electrons in two different tracks.
   
3. Finally, Chris described a modification in which tennis balls are used to represent valence electrons -- after all, the electrons are much lighter than protons and neutrons -- whereas a student represents the rest of the atom. For covalent bonding, two oxygen atoms [students under disguise, in reality] hold onto the same electron [tennis ball]. For ionic bonding of say, sodium chloride, the sodium atom [Na: represented by a soapy and squeaky-clean student] throws its valence electron [disguised as a tennis ball] to the chlorine atom [Cl represented by a sour and caustic student], representing the reaction
   Na Cl ® Na ⁺ + Cl ^-

28 January 2003: Therese Donatello [St Edwards Elementary School]      The Nuts and Bolts of Chemical Compounds 
Therese helped us understand chemical ions at a molecular level by using various types nuts and bolts to model them.  We divided into groups of about 4, and she gave each group a set consisting of 4 nuts and four  bolts. The nuts and bolts all had the same diameter, but the bolts were of various lengths.  The length of a bolt represents its "valence", corresponding to the maximum number of nuts that would fit on the bolt. A bolt of "valence two" will hold two nuts, etc.  There were various types of nuts, with square heads [Sq] or hexagonal heads [Hx].  We could use the symbol [Bo] to represent a short bolt, as well as [Bl] to represent a long bolt.  Then, the configuration with two hexagonal nuts on a short bolt is represented by the symbol [BoHx₂], whereas with two square nuts it would be [BoSq₂].

We could also "combine" the bolts by having two short bolts to share the same hexagonal nut. This would correspond to the combination [Bo₂Hx], in our symbolic notation. We could then use bolt combinations  to model chemical reactions.  For example, the reaction [combination] 2 long bolts + 2 hex nuts ® 2-2 structure could be represented symbolically as 2 Bl + 2 Hx ® Bl₂ Hx₂Note that, as an example, the "compound" Bo₂Sq₂ is represented by two short bolts attached with two square nuts, and similarly for other configurations. We are limited as to what configurations we can make with the types of bolts and nuts in question, and that reflects an intrinsic property of the corresponding chemical compounds.

A nutty but good idea, Therese!

11 February 2003: Frana Allen [Skinner Elementary School]      Matter and Atoms
Frana passed around several sheets relating to atomic structure. We began by reviewing information on matter [solid-liquid-gas, mass, density, atoms], focusing on the chemical elements:

• there are 109 elements that have been named, and each is represented by different One - or two - letter symbols
• the elements iron [ Fe] and gold [Au] are solids
• the element mercury [Hg] is a liquid
• the elements oxygen [O] and nitrogen [N] are gases

• protons and neutrons lie inside the nucleus
• electrons occupy orbits outside the nucleus.
• each proton has positive charge [+]
• each electron has negative charge [-]
• neutrons are electrically neutral [0]

Frana showed the positions of various elements on the Periodic Table [see the WebElements website: http://www.webelements.com/].   As an example, the element Potassium [found in bananas -- its symbol K comes from its Latin name Kalium] contains P = 19 protons and N = 20 neutrons in its nucleus. Its atomic number Z is equal to the number of protons in the nucleus:  Z = P. Its atomic mass, A = P + N, is given by the total number of protons and neutrons in the nucleus of the atom in question. For Potassium the numbers are Z=20 and A = 39, written as: ₁₉K³⁹.

Frana pointed out that electron orbits are arranged in various types of shells, with each shell holding a certain maximum number of electrons:

Shell Symbol	Maximum Number of  Electrons Allowed
S	2
P	6
D	10
F	14

For Potassium, K, its 19 electrons are arranged in the configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹. That is, there are 2 electrons in the (filled) 1S state, 2 electrons in the (filled) 2S state, 6 electrons in the (filled) 3P state, 6 electrons in the (filled) 2P state, and 1 electron in the (partially filled) 4S state. The chemical properties of atoms depend strongly upon the number of electrons in the partially filled states, and they are called valence electrons. Atoms with the same number of valence electrons in the same type of shell lie in columns in the periodic table, and have similar chemical properties. For example, Hydrogen [₁H], Lithium [₃Li], Sodium [₁₁Na] from its Latin name, Natrium, Potassium [₁₉K], Rubidium [₃₇Rb], Cesium [₅₅Cs], and Francium [₈₇Fr] lie in the first column of the Periodic Table and form the family of Alkali Metals.

11 February 2003: Pat Riley [Lincoln Park HS, Chemistry] pointed out that this simple electronic structure becomes more complicated beyond Z=20 [calcium: Ca], in that D shells begin to contain electrons, and the order of filling electronic shells becomes more complicated.  The filling sequence is as follows: 1S², 1S², 2P⁶, 3S², 3P⁶, 4S², 3D¹⁰, 4P ⁶, 5S², 4D¹⁰, 5P⁶, 6S², ... Beyond that point [Z=56: Barium] one begins to fill the F-shell, which may contain a maximum of 14 electrons.

Using the lovely template distributed by Frana [to see it click here], we determined and studied the structure of the chemical elements for atomic numbers Z= 1 [Hydrogen H] through Z=9 [Fluorine: F].

We learned a lot about atomic structure today.  Nicely done, Frana!

11 March 2003: Chris Clausing [Bloom Trail HS]      Inorganic Nomenclature
Chris made a Powerpoint™ presentation using the interactive CD- ROM Inorganic Nomenclature, which can be used by students on their own computers, and which tabulates scores.  The CD-ROM was obtained from the Johnson County Community College in Kansas.  For more information contact Donnie Byers: donbyers@jccc.net.

Chris modified the making compounds section of the CD by making game pieces out of cardboard to represent ions:

Terrific stuff, Chris!

06 May 2003: Joyce Bordelon [Moos Elementary School]        States of Matter
Joyce passed around a handout:  Investigating States of Matter by Making Ice Cream, prepared by Leora Baumgarten, Science Teachers Enrichment Programs, LTD 1998.

• We measured the temperature of the room air with a Celsius thermometer: +  25.7 °C
• Then we filled a large zipper bag half-full with ice, and measured the temperature inside the bag:  + 1.0 °C
• Then we added 1/3 cup of salt to the ice, sealed the bag and mixed the contents thoroughly.  We then measured the temperature inside: - 12 °C
• Next we took a small zipper bag, and put ingredients inside in these proportions.  1/2 cup milk, 1/2 cup cream, 2 tablespoons sugar.  We removed most of the air from the bag and sealed it carefully.  Then we put this small bag into the large bag, and shook the ingredients to mix them.  We then recorded the temperature inside the small bag: - 4 °C

We measured these temperatures by taking the averages of three readings.  We then removed the inside bag, and shared the contents among us, and ate them.  The ice cream was delicious!

Well organized, as well as yummy!  Thanks, Joyce!

27 January 2004: Therese Donatello  [Edwards School]         Atomic Structure:  Don't use just the Bohr Model anymore!
Terry used the LAB-AIDS INC [http://www.lab-aids.com/home/] kit Sublevel Orbitals of the Atom (Quantum Models) [http://www.lab-aids.com/home/catalog.asp?Id=105] to represent electronic orbitals that correspond to specific energy levels and sub-levels in atoms.  The following summary is given at the website listed above:

"3-dimensional model which clearly shows the position and number of electrons along the x, y and z axes as well as the orbitals of the sublevels of the major energy levels. As the students assemble the model, they will review the four quantum numbers and Pauli’s Exclusion Principle. They will identify the number and position of electrons in various atoms. Using specially designed components which simplify a rather abstract concept, students are able to observe the three dimensional effect of the model. A quantum numbers information chart is provided on each worksheet making it easier for the student to assemble the model starting with the s1 orbitals. Color-coded components help distinguish the differences between S and p orbitals. Students construct models of several common elements in the lab exercise. The models reinforce how the properties of a family of elements on the Periodic Table are a reflection of similarities in the electron configuration of their atoms."

The structure of the periodic table was greatly clarified with these models.  In a given row of the periodic table, orbitals are being filled until they contain the maximum number of electrons allowed by the Pauli Exclusion Principle.

Very thought-provoking! Thanks, Terry.

28 September 2004: Terry Donatello [ST Edwards School, Elmwood Park]          Atoms and how to show some things about atoms, even though you can't see atoms
(in a sense a version of the Rutherford gold foil experiment [http://www.chemsoc.org/timeline/pages/1911.html] )  We all welcomed Terry back with great enthusiasm!

• Terry distributed clay balls about 2 inches (5 cm) in diameter, along with toothpicks. Toothpicks were used to probe into the clay balls inside each of which Terry had hidden something. Using the toothpick probe and sticking it into the clay balls, we tried to infer what is inside without actually seeing it. Strategies included sticking numerous toothpicks into the clay balls from all different directions and with variation in the depth of sticking. The more toothpicks, the better, and some groups used  up to 20 or so to complete their probing. With regard to accuracy, our results were mixed! Objects included a wing-nut, a plastic bottle cap, and half-circle bracket.
  
• Terry had taken a shoe box and hidden something inside. She cut out the ends and replaced them with flaps of construction paper that had been cut into strips to allow a marble to go in and out of the shoe box when rolled inside, without allowing us to see what is inside. Also, the marble would ricochet backwards because of what was inside the box.  Again, this is a nice model of the Rutherford experiment.
  
• Terry put 4 steel balls or rubber balls in an aluminum pie pan, and made little indentations in the bottom of the pan to hold the balls stationary and rolled marbles down a ramp made from a 1 foot ruler to hit the balls. We tried to do a lot more similar permutations of this technique, using rubber and steel balls, as well as marbles as targets (in the pie pan) and as projectiles (rolling down the ramp).  We tried to see the results with a certain type of projectile striking a given target at a certain speed and location, etc.  Once again, very interesting!.

These were good models of the Rutherford experiment!  Thanks, Terry.

26 October 2004: Barbara Lorde [Attucks Elementary School]         Name that Element (an activity she brings us from her recent summer program at Columbia College)
Barbara started by pointing out the elements in our chart of the Periodic Table on our wall and reminding us that our own bodies are composed of many of these elements. Barbara then gave us bags of beans, each bag containing two types of beans (black for neutrons; white for electrons-protons—to simplify things, each "proton- electron pair" was represented by a single white bean). Using a periodic table, we arranged the beans in each bag to form atoms and then identified the corresponding element represented by the beans in each bag.. For example, one bag had 19 white and 20 black beans (atomic number Z = 19 and atomic mass A = 39; therefore ₁₉K³⁹, where K stands for Kalium -- the Latin word for potassium).

01 November 2005: Terry Donatello (Weber HS, retired)            Clingers
Terry showed us evidence for the cohesive force between water molecules (handout).  First, Terry poured drops of water out of a cup and onto a string held at an angle of about 30° below the horizontal. But the drops fell fell straight down.  Terry then wet the string, and tried again.  This time the drops moved slowly along the string and into the beaker below.   Beautiful!  

Neat stuff!  Thanks, Terry!