Thoughts in Black Ink

The only foreign language that I claim to know is Japanese. I started studying Japanese in elementary school and took courses throughout middle and high school as well. Simple Japanese books, everyday conversations and Japanese YouTubers are fine for the most part, but vocabulary is still a problem for me. While at work the other day, I decided to practice some new terms I read on a blog post.

Fig. 1: Vocabulary practice (orig.)

Papers covered in words like this are scattered all over my room. Sometimes the need to write just gets to you, you know? Staring at the scribbled words, I suddenly thought, what is this stuff I’m writing with anyways? 

Ignoring the fancy colors, black pen ink is a relatively simple composition made of carbon black suspended in drying oils, alcohols or petroleum products [1]. Carbon black is carbon powder obtained by burning organic matter. This type of black ink has been around for thousands of years, and I use another form of the same stuff while doing Japanese calligraphy. East Asian calligraphy ink is traditionally made of pine soot (carbon black) mixed with bindings and herbs. This page provides a more in-depth description of how sumi, or a Japanese ink stick, is made.

Fig. 2: Carbon black sample molecular structure (Bruno Glaser)

So why is carbon black... black? Writer Maggie Koerth-Baker does a good job of describing this. In organic chemistry, pi-conjugated systems, or systems where electrons of sp² hybridized atoms are delocalized in combined p-orbitals, can exhibit a wide range of light absorption and emission properties. This is because of the many possible bonding and antibonding p-orbital orientations within the conjugated system.

Fig. 3: Molecular orbital states for benzene (Michigan State University)

When we talked about why excited metals emit colored light back in The Dazzling Chemistry of Fireworks, we mentioned that the Fermi level of metals is located within an electronic band, meaning that electron transitions between the highest occupied energy level and other higher energy electron states are possible over a range of values. The many available higher energy electron states are not unlike the many possible organizations of bonding and antibonding orbitals in pi-conjugated systems. An incident photon on a pi-conjugated system can upset the shared p-orbital system into occupying one of the possible antibonding arrangements, later to reemit the light energy at lower, sometimes non-visible spectrum, wavelengths. Pi-conjugated systems that include more atoms result in more complex molecular orbital states. And when conjugated units of varied length exist together in a material, then on the whole even more electronic states are possible! All of these electron transitions cooperate to make the familiar black ink of pens (graphite pencils too, just think about it).

If you enjoyed this post and those I've written before, share your thoughts in the comments to let me know!

Party Science, Part 2: The Lights

If you haven't already, please read Party Science, Part 1: the Beats.

So, now that we’ve got the beats, what’s next? How about we get some lights to set the mood. Today’s installment: the lights.

Again we’ll start with a simple question: what is light? Simple question, not so simple answer. To skip a lot of gritty stuff, let’s just start with the premise that light is a form of electromagnetic radiation consisting of orthogonal electric and magnetic field components and behaving as a transverse wave while also as a particle… yeah. Anyways, there are many types of light bulbs that we can use for different effects. For typical houselights, incandescent bulbs with tungsten filaments that utilize blackbody radiation were used until recent years. Currently, compact fluorescent light bulbs (CFLs) are popular for efficiency reasons with LEDs on the rise. CFLs work by ionizing argon gas and mercury vapor with tungsten filaments by thermal electron emission to produce UV radiation. The UV radiation is then converted to visible white light by phosphors either on the bulbs or on their housing [1]. LEDs utilize the junction between semiconductor material doped with electron rich or electron poor elements relative to the semiconductor valence number (p-n junction) to produce light as the electrons from the negatively-doped material fall into lower-energy electron "holes" in the positively-doped material. With these typical lights we have some basic lighting. Now what are we going to do about colorful lights for that true party feel? The college DIY option would be to put colored plastic or something over house lights to get the same effect as a colored bulb at a fraction of the cost!

Fig. 1: Procedure for colored lamp perfection (Dornob)

But how does doing this produce colored light? The first thing to notice is that the colored filter is, in fact, colored (huh, imagine that). What this indicates to us is that whatever the material is made of or coated with, it is only transmitting light that comprises the observed color. In other words, the material is absorbing a portion of the visible spectrum of light and we see a net color as a result of this absence. This could be due to a number of factors, for example the presence of transition metal compounds or conjugated organics, but the general property that allows a material to absorb light is a possible electron energy state transition corresponding to a frequency in the visible spectrum. When applied, the colored filter acts on the white light emitted from the light source, filtering out the characteristic absent spectrum and producing a net color. And with our bargain colored lights in place, how about we go for a special effect to top it all off. Let's use some blacklights. Blacklights are fluorescent lamps tubed in black-coated glass to absorb most visible light and coated in phosphors that permit only UVA light (not UVB, which causes sunburn, or UVC, which is filtered out by our atmosphere naturally and would give you super sunburn, a.k.a. cancer) to exit. The UVA radiation produced interacts with phosphors in white clothing from laundry detergents, with natural phosphors in teeth and nails and with fluorescent clothing to produce the psychedelic colors that are associated with blacklights [2]. With beats and lights, our party is going strong.

Below I’ve posted a video of Russian hip hop artist Kristina Si that depicts multiple types of lights employed at a party. Take notes people. 

The Dazzling Chemistry of Fireworks

Yesterday was the Fourth of July, and millions of people all over America gathered in parks and along waterways to witness one of the most dazzling examples of ancient science; fireworks. The invention of gunpowder in China ca. 600-900 CE resulted in the creation of the first fireworks, later buffed up to the colorful sky-flowers we know today by Italian fireworks makers in the 1830s [1]. While waiting for a fireworks display at the Philadelphia Museum of Art, I found myself wondering how is it that we humans have come to create this technology. The first step was to devise a method of controlling highly exothermic and expansive (due to gas formation) chemical reactions and initiate them on purpose through the use of chemical oxidizers (originally saltpeter, KNO3) that contribute oxygen to combustion reactions, allowing them to burn in containers without oxygen flow or even in vacuums. But the role of gunpowder in history has had many uses beyond fireworks and isn’t what makes this specific variety of chemical explosions so addicting. What gives fireworks their characteristic hues are the metal ions that exist along with the crafted gunpowder in fireworks shells. Italian fireworks makers discovered that the use of KClO3 rather than saltpeter could increase the temperature of the combustion reaction, allowing for the light-emitting potential of metal ions to be unleashed [2]. When calculating the standard enthalpy of reaction for the following decompositions;

1.     2KNO3 --> K2O + N2 + 2.5O2

2.     2KClO3 --> 2KCl + 3O2

it can be observed that the decomposition of KClO3 is more exothermic than that of KNO3 (625 kJ/mol for KNO3 and -89.6 kJ/mol for KClO3 based on standard enthalpies of formation found on Wikipedia), the former also generating 0.5 more moles of O2 gas than the latter. The extra oxygen gas contributes to the exothermic nature of the combustion through the formation of CO2 and SO2 gas (-393.5 kJ/mol for CO2 and -296.81 kJ/mol for SO2 based on Wikipedia values), the same source of energy from which coal power plants operate, according to the following equations:

3.     C + O2 --> CO2

4.     S + O2 --> SO2

The color that a given metal salt produces when heated is characteristic of the metal element and can be calculated based on the following equations [3,4];

5.     E=hv 

6.     c=lv (v=fl modified for light)

7.     E=hc/l (from equations 5. and 6.)

8.     E=-Rhc(1/(nf)^2-1/(ni)^2) (Rydberg Formula*)

*note: UC Davis source seems to consolidate the Rydberg Formula hc term into the Rydberg constant, as evidenced by their subsequent derivation eliminating the hc term against the value of R.

Fig. 1: Sodium electron orbital energy diagram (Whitman College)

From the above electron orbital energy diagram for sodium, it can be seen that the transition between the highest occupied molecular orbital (HOMO), the 3s orbital, and the lowest unoccupied molecular orbitals (LUMO), the 3p set, corresponds to an emission of light in the 589nm wavelength region, or yellow light. This fact is experimentally verified since the yellow color of fireworks is often produced by sodium salts. It is in this fashion that the colors each metal element produces can be understood. So why metals? Well, the emission of light in various visible colors is reliant on electron energy state transitions as we just discussed, and electron band structure properties for metals tell us that the Fermi level, or highest occupied energy level (HOMO energy level), lies in the middle of an electron band in metals, meaning that there are higher electron energy levels to which metal electrons may be excited [5]. So metals are used simply because in our universe these are the elements that are capable of light-producing electron transitions.

Of course other factors must go into fireworks to achieve such controlled chemical acrobatics as producing tailed explosions or glittery rain, but with bang and color you have the basic makings of this recreational technology that is also a marvel of modern chemistry. 

I plan to do experiments inspired by daily events or questions that arise, so comment if this post has brought up any topics you would like to hear more about or want to see experiments on. Thanks!