Tag: chemistry

“The metals are elements wondrous:
At room temp, most, solids; dense; lustrous;
Also ductile, conductive.
But this form’s reductive;
In textbooks: more info, illustrious.”

The 22 October 2019 limerick was part of the National Chemistry Week 2019 sequence, focusing on another aspect of “Marvelous Metals.”  

“The metals are elements wondrous: /
At room temp, most, solids; dense; lustrous; /
Also ductile, conductive…”
Chemistry textbooks compile much technical information in a relatively small space; this limerick takes this a step further, cataloging several traditional definitions and properties of metals via the syllabic constraints of a limerick.  

Metals exist in the solid phase at room temperature, with the notable exception of mercury.  Metals’ densities are high: even a small volume of a given metal has a significant mass (and these densities are characteristic to specific metals, as commemorated in Archimedes’s famous realization).  Metals are lustrous, reflecting light and appearing shiny.  They are ductile and can be turned into wires; they can conduct heat and electricity.  [As a sidenote, textbooks generally mention ductility (a metal’s ability to be made into a wire) and malleability (a metal’s ability to be flattened into a sheet) in the same sentence, but I couldn’t fit the latter property into this space.]          

“But this form’s reductive; /
In textbooks: more info, illustrious.”
The last two lines are a bit contradictory: they acknowledge the limits of the limerick and point an interested reader towards the more expansive information discussed in textbooks… even as the inspiration for the limerick arose from the brevity with which these books address metals’ many interesting properties, in introducing the periodic table.  

Usually, however, a textbook will include more extensive discussions of descriptive chemistry as well; these chapters expand on the general discussion of metals provided in the early overview, examining particular groups’ chemical and physical properties.  Likewise, some of the other limericks written for this week will address specific metals in more detail.       

“The marvelous metals are able
To make up quite a lot of the table
That we term periodic:
Collection symbolic 
Wherein lies each element’s label.”  

The 21 October 2019 limerick was written as part of National Chemistry Week 2019. It provides an overview of the periodic table of the elements (PTE), the relative populations of metallic and non-metallic elements on the PTE, and the use of chemical symbols on the PTE.   

“The marvelous metals are able /
To make up quite a lot of the table /
That we term periodic…”
A wide number of chemical properties and principles can be gleaned from an understanding of the periodic table of the elements (PTE).  For instance, metallic character versus non-metallic character can be assessed: the left side of the PTE includes metals, and the right side of the PTE includes non-metals.  Roughly 80% of the elements are metals; they thus “make up quite a lot of the [periodic] table.”  The dividing line between metals and non-metals is often referred to as a “staircase,” given its appearance; the semimetal or metalloid elements are collected in this range of the PTE.  

“Collection symbolic /
Wherein lies each element’s label.”
The periodic table uses chemical symbols as a convenient shorthand for the element names; the label for each element is a one-letter or two-letter symbol. 

Sometimes, these labels are predictable given the name of the element, as with cobalt (Co), for which the symbol is intuitive.  Other times, the labels reflect a name expressed in a different language, as with iron (Fe) and potassium (K); both of these take their abbreviations from the Latin words for the elements (ferrum and kalium, respectively).  The title of this piece alludes to the idea that these instances can seem frustrating and dissonant, as one is learning chemistry; the idea of “metallic symbols” here provides an intriguing play on words with “metallic cymbals.”

As with an introductory approach to any subject, some degree of memorization is inherent and important in learning to use the periodic table efficiently as a disciplinary tool.    

“Today starts a week that will readily  
Spotlight highlights for seven days, steadily,
As we celebrate nationally
Our science that rationally
Explores matter’s properties: chemistry.”

The 20 October 2019 Twitter poem began a series of poems written to celebrate National Chemistry Week 2019.    

“Today starts a week that will readily /
Spotlight highlights for seven days, steadily…”
As with Chemists Celebrate Earth Week, which I’ve written about in this space previously, National Chemistry Week is a celebration sponsored by the American Chemical Society.  I had not realized its longevity until writing this piece; the first occurrence was in 1989.  Each year, the week has a different theme, highlighting such myriad topics as chemistry and art, environmental chemistry, and nanotechnology.    

“As we celebrate nationally /
Our science that rationally /
Explores matter’s properties: chemistry.”
The theme of the 2019 National Chemistry Week was “Marvelous Metals,” as will be seen over several upcoming entries here.  This year, National Chemistry Week will be held from October 18-24 and will focus on “Sticking with Chemistry”: the science behind glues and adhesives.  The American Chemical Society provides a wealth of educational resources and activities each year to celebrate the pertinent theme, sponsoring events across the USA.  Chemistry examines the structures, properties, and reactions of chemical species, commonly phrased as the study of matter.    

(“Chemistry” is a word that doesn’t perfectly rhyme with too many others.  One of the rhymes I tried in an early draft of this limerick was “centrally,” building on chemistry’s characterization as a “central science.”  I was most familiar with this phrase in its capacity as part of a popular textbook title; again, it was interesting in drafting this essay to realize some larger discussions of that phrase.  As one might suspect, the connections between different STEM disciplines are complex and oft-debated!)   

“To consider electrons’ repulsions
In geometries under construction,
VSEPR theory
Provides first steps; here, see 
To molecular shapes, introduction.”  

The 14 October 2019 limerick alludes to a theory used in introductory chemistry courses to rationalize molecular geometries.   

“To consider electrons’ repulsions /
In geometries under construction…”
Yet another big idea in General Chemistry is that of molecular geometry: the three-dimensional shape in which a molecule exists.  The shapes of molecules have major implications for how these molecules can react and interact with one another, and so being able to predict a molecule’s geometry is an important first step for understanding its properties and reactions.  Three theories are typically introduced to rationalize molecular geometries: valence bond theory, molecular orbital theory, and valence-shell electron-pair repulsion theory.  All involve to some extent the central idea that negatively charged electrons repel one another.  

“VSEPR theory / 
Provides first steps; here, see /
To molecular shapes, introduction.”     
In general chemistry textbooks, the chapter on molecular geometry is a chapter in which Bent’s discussion of “strange terms for strange things” often seems particularly apt.  The three theories mentioned above are referred to as their abbreviations: VB theory, MO theory, and VSEPR theory, respectively.  (Further confusing the issue, VSEPR is often pronounced “vesper”!  However, in this poem, the rhyme scheme relies on spelling out the acronym.)       

VSEPR theory is the simplest of the three and is generally extensively explored in introductory coursework, providing important “first steps.”  As alluded to above, VSEPR stands for “valence-shell electron-pair repulsion.”  Valence electrons are the outermost electrons of an element; when elements combine into molecular compounds, the valence electrons participate in covalent bonds (with each bond involving two electrons) or exist in “lone pairs.”  In all of these cases, the electron pairs from the valence shells repel.  This ultimately results in characteristic shapes for molecules, as electron pairs will distance as far away from one another as is geometrically possible.   

“The property known as chirality:
A helix’s handed spirality;
Two non-superposing
Mirrored molecules, chosen
To label by dext/sinist-rality.”  

The 23 September 2019 limerick addressed an interesting property observed in three-dimensional molecules, which is introduced in organic chemistry coursework.   

“The property known as chirality: /
A helix’s handed spirality…”
Organic Chemistry 1 is a challenging course for many reasons, one of which is the necessity of thinking about three-dimensional molecules and properties via largely two-dimensional communication: textbooks and chalkboard drawings.  One property that demands the ability to think three-dimensionally is chirality.  

It is obvious when someone puts shoes on the wrong foot or gloves on the wrong hand.  Feet and hands are chiral: they are non-superimposable mirror images.  Some molecules exist in “handed” forms, which means they react differently in “glove-like” chemical environments: some fit and some don’t.  Other molecules are achiral; they do not exhibit this quality.  (I’ve always liked the succinctness of “shoes are chiral; socks are achiral.”)   A DNA molecule, with its spiraling helix, is chiral, providing a pertinent rhyme.

“Two non-superposing /
Mirrored molecules, chosen /
To label by dext/sinist-rality.” 
Several precise vocabulary terms are introduced via topics of stereochemistry.  Molecules that are stereoisomers are molecules made up of the same atoms bonded in the same order but with different three-dimensional arrangements.  Stereoisomers that exist as pairs of the non-superimposable mirror images described above are called enantiomers.  Specific stereocenters (locations where chirality is evident) are distinguished as having “R” or “S” orientations.   Many such terms are used in organic coursework.    

Along with R/S notation, chiral molecules can also be described in terms of their optical rotation: the direction in which they rotate plane-polarized light, which is described with a positive or negative sign.  These terms are dextrorotatory (clockwise rotation) and levorotatory (counterclockwise rotation).  To fit the limerick’s rhythmic constraints, “dext/sinist-rality” was used as a shorthand for this last set of “handed” definitions.    

“Quantum numbers disencumber
Orbital descriptions.  
Combinations’ denotations: 
3-D space depictions
From wavefunctions.  Numbers’ junctions 
Address volumes probable.
Useful tools are Q. N. rules,
To name electrons’ ‘domiciles.’”

The 16 September 2019 Twitter poem highlights a useful metaphor for considering atomic orbitals (mathematical functions that describe electron behaviors) in General Chemistry.  Since the actual math describing atomic orbitals will not be seen until higher-level chemistry coursework, it can be challenging to discern the uses and descriptions of these models at the introductory level.  

“Quantum numbers disencumber /
Orbital descriptions.”  
Matter functions differently from our everyday experience at the atomic and subatomic scales: whereas the equations of classical mechanics work well in describing everyday observations, the equations of quantum mechanics are used to describe the particulate-level scale.  Electrons are subatomic particles, and their locations are described in terms of probabilities; rather than the exact path delineated by an “orbit,” an electron’s location is within an “orbital.”  An orbital is described by a combination of quantum numbers (n, l, and m_l).  Each number relates to a different aspect of the orbital: combined, they establish its size, shape, and orientation in space.  (A final quantum number, m_s, identifies the specific electron within its orbital, via that electron’s spin.)  A combination of quantum numbers specifies an orbital of interest, “disencumber[ing]” its description.   

“Combinations’ denotations: /
3-D space depictions /
From wavefunctions.  Numbers’ junctions /
Address volumes probable.”    
By manipulating the mathematical function associated with an orbital (called a wavefunction), a three-dimensional shape results; this shape represents, with 95% certainty, where an electron will be.  Each specific “3-D space depiction” is denoted by the combination, or “junction,” of the three quantum numbers (n, l, and m_l) described above; a common metaphor is an address for an orbital’s “volume probable.”     

“Useful tools are Q. N. rules, /
To name electrons’ ‘domiciles.’”
Quantum numbers and the rules describing them give us a succinct way to identify the “domicile” of an electron: the orbital in which it “resides.”  While such imagery is, of course, not nearly as precise as the mathematics used in advanced coursework to further explore atomic orbitals, this analogy provides an accessible and important step for students in understanding the concept.