Periodic Table of Desserts

I have to thank a geek girlfriend of mine, Alison from North Carolina who submitted this "did-you-know" link. A place of posters that you can order which present the Periodic table of desserts, vegetables, fruits and endangered species. A super cool place to wander for Christmas presents. This is just an FYI when you're having a hard time finding that just-right gift for your scientific friend (or is that fiend?)

Enjoy!

Geek Think: How Scientists Approach the World

Almost there, aren’t we? Congratulations. Now, at last, it is time to consider why you have been taking this class.

A few facts about chemistry is one good reason. Learning how to think like a scientist is the other.

Today we will be addressing the second point, the fine art of honing the geek mind. We will approach this subject by example, by going through the experiment that was assigned a couple of sessions ago. The following little piece constitutes my own effort at completing the task, with a few editorial comments thrown into spice the stew. Naturally in the normal order of things all of this would be recorded in a laboratory notebook so that you could sign and date the entries, to protect your important insights from competitors in the Alka-Seltzer analysis field. You will just have to settle for reading about it on line.

Let’s start with HYPOTHESES. I came up with two:

Two-tailed: Altering the reaction temperature will alter the reaction rate.

One-Tailed: The reaction will increase as the reaction temperature rises.

A two-tailed hypothesis is one that makes no assumption about what outcome will occur (i.e., a rising reaction temperature will alter the rate either up or down), while a one-tailed hypothesis picks a specific way in which you think the outcome may trend.

The next thing a good experiment needs is a list of MATERIALS. I include separate headings for reagents (the stuff that participates in and/or is consumed during the chemical reaction – in this case Alka-Seltzer and water) and equipment to perform the experiment (clear glass, 1-cup measuring cup, watch with second hand, thermometer). The materials list is followed by a really detailed, step-by-step set of METHODS. One must pay great attention to detail in this section so that (1) you can catch any mistakes you have made in running the experiment and (2) so that other people can replicate your work. In science, if it can’t be repeated is not considered reputable. The methods I used for this experiment were, in order, the following:

1. Alka-Seltzer tablets were unwrapped two at a time.

2. Water was prepared as follows:

a. Cold (~0°C): Four 1-in³ ice cubes were added to four cups of water and left for 15 minutes

b. Normal (~20°C) Four cups of water were decanted from a receptacle after sitting for 24 hours at room temperature

c. Hot (~100°C) Four cups of tap water were heated to boiling in a teapot

3. The glass was equilibrated to the desired water temperature by pre-filling with either ice water or hot water.

4. One cup of water at the appropriate temperature was placed in the glass. A 1-in³ ice cube was added to the “cold trials” to keep the water cold.

5. A single tablet was dropped from a 2-inch height into the vessel.

6. Time (in seconds) to complete dissolution of the primary tablet (i.e., the end of violent fizzing) was recorded.

7. Ancillary (“other”) measurements included observations on tablet motility and gas evolution.

Of course, the point of an experiment is to get some RESULTS. These are the ones I got. I put them into a table so that the raw data (the values measured during all the trials) would be available for inspection. Then I calculated the mean (the average) of the results for each temperature so that someone wanting to quickly see the outcome would be able to do so at a glance.

	Temperature
Trial	0°C	20°C	100°C
1	87 s	47 s	34 s
2	100 s	45 s	33 s
3	80 s	49 s	32 s
4	66 s	49 s	32 s
Mean	**83	48	**33
SD	14	2	1

The double asterisks (**) denote that the mean values for these two groups are significantly different from the mean value for the 20°C group, p < style=""> (Normally, statistical significance is assigned to an outcome if p <>

I made a few additional observations on characteristics of Alka-Seltzer. These traits were not the focus of my hypotheses, so I did not measure them exactly. However, I made some reasonable “guesstimates” regarding their repeatability so that I could investigate them in more detail.

1. Tablet motility varied by temperature. Tablet orientation became:

a. Cold (~0°C): Vertical at 45 to 50 s

Floated at 55 to 60 s

b. Normal (~20°C) Vertical at 15 to 20 s

Floated at 20 to 25 s

c. Hot (~100°C) Vertical orientation not seen

Floated immediately

2. Tablet character upon cessation of fizzing.

a. Cold (~0°C): Many small particles and much foam cover most of the surface

b. Normal (~20°C) A few fine particles and some foam line the rim of the glass

c. Hot (~100°C) No particles or foam remain

3. Gas evolution varied by temperature.

a. Cold (~0°C): Fine bubbles made from top of tablet, large ones from beneath

b. Normal (~20°C) Fine bubbles made from top and bottom of tablet

c. Hot (~100°C) Myriad fine bubbles from entire surface of tablet, as well as elaboration of steam from upper surface

Finally, you use the results to make an INTERPRETATION. This step is also called drawing conclusions or making inferences. In this case, my results confirmed the hypotheses I made: the rate of a chemical reaction is significantly increased as the reaction temperature is raised.

A word on STATISTICS. Mark Twain popularized the Benjamin Disraeli proverb, “There are three kinds of lies: lies, damned lies, and statistics.” This statement is knocking statistics, but those who would use a mass of poorly understand numbers – even if correctly calculated – to support an inaccurate conclusion. Scientists rely on statistics to avoid false positive and false negative conclusions. A false positive or Type I error occurs when the statistical calculation suggests that something is of significance but in reality it is not, while a false negative or Type II error occurs when something significant in the real world is not identified as such using the statistical analysis. In general, scientists tend to try to avoid the Type I error more vigorously. A detailed consideration of statistics s way, way, way beyond the scope of this blog. Just keep in mind that statistical calculations can be used by different scientists working on the same problem to bolster totally opposite points of view. Just because a number is thrown at you, don’t believe that the “answer” it is trying to reinforce is true. The concept caveat emptor – “Let the buyer beware” – is particularly true in science. Be open to new ideas, but be skeptical about adopting them without a thorough review of the data for yourself.

Sleep tight. It all ends tomorrow. The class, I mean….

The Universe Within: Quantum Chemistry

Halfway there after today, folks. Hang in there.

The topic for this morning is a continuation of the periodic table, particularly the chemical properties of the major elements and the subatomic structure of the atomic nucleus.

The main topic to consider in mastering the modern periodic table in its relationship to quantum mechanics is how to describe electrons in the nucleus. Each electron has a unique address in the electron cloud, a position in an orbital. Each orbital, or shell, is a wave function describing the likely location of electrons based on the lowest possible energy state of the nucleus. We cannot know precisely where any given electron is in an orbital as stated in the Heisenberg uncertainty principle, but we can still describe it numerically. Modern quantum theory holds that each electron orbits the nucleus in a specific shell and sub-shell with a given orientation. Thus, each electron has a unique “address” composed of four quantum numbers.

The principal quantum number, n, defines the shell in which the electron resides. Values of n are positive, non-zero integers. The shells with n = 1, n = 2, and n = 3 are called the first shell (also called the K shell, for no particular reason), second shell (L shell), and third shell (M shell). The secondary quantum number, l, divides each shell into sub-shells of slightly different energies. For a given orbital n, the l values can range from 0 to (n – 1). Thus, for the first shell (n = 1), the only value of l is 0, and only one sub-shell exists; for the second shell (n = 2), values of l can be 0 or 1, and two sub-shells are present; and so on. The sub-shells are designated by a letter code, where the first (l = 0) is labeled “s”, the second (l = 1) is “p”, the third (l = 2) is d, the fourth (l = 3) is “f”. To designate a particular sub-shell, we write the principal quantum number followed by the letter code for the sub-shell. The lower the sub-shell number, the lower the energy. The third quantum number is known as the magnetic quantum number and is designated m_l. It divides each shell into individual orbitals. Values for m_l can range from +l to –l. Thus, the s sub-shell (l = 0) has a single orbital since +0 and -0 are still just 0, while the p sub-shell (l = 1) has three orbitals (+1, 0, -1). All the orbitals of a given sub-shell have the same energy. The fourth quantum number is the spin quantum number, m_s, which is either + ½ or - ½. The Pauli exclusion principle states that no two electrons in the same atom can have identical values for all four quantum numbers.

Atoms are built from the inside out, by adding electrons to the lowest possible orbital because this is the lowest and therefore most favored energy state. This concept is termed the aufbau principle (German for “building up”). When added to a specific orbital, Hund’s rule states that electrons will spread out as much as possible, avoiding pairing within an orbital for as long as possible.

The interaction of atoms in chemical reactions is dictated by the electron configuration in the outer (or valence) shell. Elements in the same group (column) of the periodic table have similar arrangements of electrons in their valence shell. The valence shells fill as one progresses from left to right in the periodic table, until all positions are occupied in the VIIIA group (noble gases) located farthest to the right. The completely filled valence shell of the noble gases renders them quite unreactive. Many other elements undergo chemical reactions in such a way that their electron configuration tends to assume the same configuration as the nearest noble gas.

Rest well until tomorrow – in body, if not in mind.

The Big Picture: Chemistry Gets Organized

One day down, four to go. Let’s rock on.

The major topic for the next couple of days is MODERN ATOMIC THEORY. Chemistry did not begin until this principle had gained general acceptance in the early 1800s . The first recorded hypothesis regarding the basic unit of material things is attributed to the pre-Socratic Greek philosopher, Democritus (c. 460–c. 370 B.C.). After his teacher Leucippus had noted that a beach looks smooth from afar but really consists of individual sand grains, Democritus said that the concept could be extended to all matter because material things were made of indivisible particles. Democritus called his particles atomos, meaning "cannot be cut." His ideas were largely ignored until the scientific revolution of the western Enlightenment (16^th to 18^th centuries) due to widespread acceptance of Aristotle’s (c. 384–c. 322 B.C.) view that all matter was comprised of earth, air, water, and fire in varying proportions, and that matter could be transmuted into gold by adjusting the ratios of these four elements. (Aristotle also limited matter to four essential properties: hot, cold, dry, and wet!)

In modern times, atomic theory was rediscovered by John Dalton (1766-1844), an English physical scientist. In the early 1800s he was a professor of mathematics and natural philosophy, and he dedicated his research efforts to standardizing then known chemical knowledge. The result was a series of principles to explain the structure of matter:

1. Matter consists of tiny particles (atoms).
2. Atoms are indestructible. In chemical reactions they can rearrange but not break apart.
3. All atoms of a given element are identical in mass and other properties (true then, as isotopes had not been discovered).
4. Atoms of different elements differ in mass and other properties.
5. Elements combined into a given compound always react in a fixed ratio.

The atomic theory provided the impetus for later attempts to develop a unifying principle for all chemistry (and physics!) knowledge, the PERIODIC TABLE. Many scientists in the late 1700s and early 1800s contributed to its theoretical underpinnings, but the laurel for the first modern version goes to Dmitri Mendeleev – to give the most common of the spellings for his name). This Russian chemist is accorded the honor because his array not only attempted to systematize existing chemical knowledge but because he used his model to make predictions about the existence and properties of then unknown elements. Mendeleev arranged his table into columns (groups) and rows (periods) according to elemental atomic weights (representing the mass of protons and neutrons), while modern tables use atomic number (proton number). Entities in a given group or period share certain chemical properties based on their atomic structure, and particularly the number and arrangement of electrons in the outer (or valence) orbital. But more on that tomorrow….

Chemistry Experiment

Chemistry AS403 – Experiment

Chemical reactions proceed at a set rate, but the rate varies depending on many factors. Environmental conditions in particular have a major impact on the rate at which reactions may proceed.

Undertake the following experiment at home to test this principle.

Buy a box of Alka-Seltzer anti-indigestion medication. This product combines acetylsalicylic acid (aspirin), sodium bicarbonate (baking soda) and citric acid.

You will be conducting an experiment with 3 tablets. Place one tablet in a glass of hot (but not boiling) water, another in a glass of ice-cold water, and a third in a glass filled with water that is at room temperature. Measure how long the fizzing continues in each glass after dropping the tablet.

Prior to the experiment, construct hypotheses about (1) the likely outcome and (2) the mechanism by which the fizzing is produced. After gathering data, interpret your results, design any follow-up experiments that might be needed to refine the data, and make a list of factors that might have impacted the accuracy of your experiment.

Feel free to use the left-over Alka-Seltzer to sooth your heartburn....

Simulation on Public Policy

Chemistry AS403 – Simulation

Washington, D.C.

Spring, 2019. The one bright spot in the usual atmosphere of political infighting and intrigue is public contentment with the austere homeland security policies that finally succeeded in interdicting illegal immigration across the nation’s 2000-mile southern border beginning in 2013. This success was achieved through the combined use of multiple electrified fences backed by solid concrete walls, with regular defoliation of the intervening no-man’s-land between the barriers using biodegradable herbicides.

In 2014, the United States had suffered a severe bout of inflation due to the rise in wages associated with the loss of several million “guest” workers, while Mexico underwent a major recession due to many factory closures stemming from the loss of major American markets. Mexico responded by suspending diplomatic relations with the United States. Relations were restored in 2017 thanks to the efforts of the newly elected Administration, which moved rapidly to restore free trade (but not immigration). Mexican factories in border towns were reopened, and the adjacent border became the main route for transporting Mexican goods to the eager American consumer. The entire free trade zone along the Texas – Mexican border developed almost overnight into an economic powerhouse to rival the success of South Korea and Taiwan. Communities on both sides of the border are benefiting by the rapid increase in employment, income levels, and public services. The flagship accomplishments touted by governmental officials in both nations are ample schools and libraries, low-cost medical clinics, and careful environmental stewardship.

Despite the promise, a concern for the region’s population is the rising number of birth defects in infants and cancers in people of all ages. The problem has been smoldering for nearly three decades, but in the last five years the incidence has accelerated rapidly. The local economies are in danger of collapse as potential workers avoid relocation to the region while the incumbent population seeks to leave.

You are a member of a bilateral public policy commission tasked with identifying likely cause of the epidemic and pinpointing means by which the threat may be ended. Develop one or more hypotheses regarding the cause of the problem. Design the necessary tests to verify or negate the hypotheses, keeping in mind both scientific considerations and ancillary concerns (e.g., cost and international relations). Prepare a brief for delivery to the President outlining your hypotheses, proposed experiments (both initial and follow-up), and likely recommendations for dealing with the scenario.

Fundamentals of Chemistry, Day #1 Lecture Notes

Chemistry AS403 – Lecture 1 Notes: Fundamentals of Chemistry

Okay, let the good times roll. Today we cover the basic tools one needs to start taking a crack at chemistry.

Let’s start with VOCABULARY, some simple definitions that will put all of us on the same page as the game gets underway. In alphabetical order:

• Accuracy = closeness of a measured value to the true value
• Atom = the smallest particle of an element (Gr. atomos = “uncut”)
• Chemistry = a science that investigates the composition of materials and how their properties change by their environment
• Compound = substance combining fixed proportions of 2 or more elements
• Density = ratio of an object’s mass to its volume
• Element = a substance that cannot break into a simpler one
• Energy = a quality allowing an object to do work. The two main classes:
• Kinetic = energy in a moving object
• Potential = stored energy (which can be converted to kinetic type)
• Heat = energy that is transferred among objects with different temperatures
• Law = a broad generalization known by experimentation to be true for all people and all times
• Mass = the quantity (NOT weight!) of a given substance
• Matter = anything that occupies space and has mass
• Mixture = material combining variable proportions of 2 or more substances
• Molecule = Smallest particle of a compound
• Precision = closeness of repeated measurements to each other
• Property = characteristics unique to a given substance. Two types are:
• Chemical = trait that can change as a substance reacts with others
• Physical = trait that can be observed without changing the substance
• Specific gravity = ratio of a substance’s density to that of water
• Temperature = property proportional to the average kinetic energy
• Theory = a well-tested explanation of a natural phenomenon
• Weight = the force with which a substance is attracted by gravity
  

Once we have a common lingo, we need some other COMMON PROCEDURES. Chemists, indeed all scientists, use the following tools each and every day. The “Big Three” pieces in the tool kit are the International System of Units (SI), Significant Figures, and Scientific Notation.

The SI scheme offers standard units of measurement for seven basic quantities. The most common in the chemistry laboratory are for length (meter, m); mass (kilogram, kg); time (second, s); temperature (kelvin, K); and amount (mole, mol). The base units can be modified by adding prefixes and suffixes, the most typical of which are mega (10⁶, M); kilo (10³, k); centi (10^-2, c), milli (10^-3, m), micro (10-6, m), and nano (10^-9, n). Conversion factors are used when necessary to convert between the various units. Examples for length and volume (with derived units of length cubed) include:

1 m = 100 cm = 1000 mm

1 m³ = 1000 L (where L = liter)

1 L = 1000 cm³ = 1000 mL

Significant figures are those which have been accurately derived by careful measurements. The number of significant figures in a measured value is equal to the number of digits known for certain plus one that is not totally certain. The higher number of significant figures, the greater the degree of precision.

Scientific notation is a shortcut for writing very large or very small numbers. In science, the standard use is to write numbers to base 10, using exponents. As an example, an electron (a very small subatomic particle) has a mass of about 0.000 000 000 000 000 000 000 000 000 000 910 kg. In scientific notation, this number is rendered as 9.10 x 10⁻³¹ kg. Simple rules for working with exponents allow scientists to manipulate numbers easily when working with minute samples and very rapid reactions.