Thursday, September 14, 2017

Food From Toxic Cycads



The Chamorro people of Guam were suffering from a terrible disease that resulted in paralysis, dementia and death.
As the Chamorro became more “Americanised”, fewer people were dying from this disease. Researchers started to look closely at traditional Chamorro food to find the compounds causing the disease. They thought they had found the answer, flour made from the seeds of toxic cycads.
But, there was a problem. Cycad seeds are used by many traditional communities all over the world as food. Why didn’t these other people get sick and die?

Read more in the September 2017 edition of AUS-e-NEWS:

Sunday, September 10, 2017

I Hate STEM Education!

You might think it strange that I hate STEM education since I spend my life encouraging people to study chemistry. It's not the education part I hate, it's the acronym "STEM" and what it stands for.

I recently read an article by Bryan Scaf, "STEM - We know what it stands for, but what does it mean?" (https://au.educationhq.com/news/40140/stem-we-know-what-it-stands-for-but-what-does-it-mean/).
Which started me wondering if we really do have  a shared understanding of the meaning of STEM.
What STEM means depends on who you are talking to.

If you ask a scientist, they will probably tell you that STEM stands for a Scanning Transition Electron Microscope and the first STEM was built in 1938.
If you try asking people in the street, they are most likely to think it has something to do with biology, plant stems or stem cells for example.
Towards the end of the twentieth century, STEM started being used as an acronym for Science, Technology, Engineering and Mathematics (STEM), superseding the previous (and possibly slightly  less ambiguous) SMET acronym. STEM education has come to mean an integrated approach to the teaching of science, technology, engineering and mathematics using an inquiry-based learning model.
So the question arises of whether we  do indeed know what STEM stands for.
In case you are not convinced that "STEM" is ambiguous, head on over to http://www.acronymfinder.com/STEM.html and read through their list of 19 uses of the acronym STEM.
The first reason why I hate STEM is that the term is ambiguous.

STEM (as science, technology, engineering and maths) is a huge area. It encompasses observable, concrete entities as big as the entire cosmos and as small as elementary particles, and, that's just the STE part!  The "M" part is quite nebulous (yes, groan, groan, another bad pun).  Maths is based on numbers, shapes and other abstract entities. So when we lump abstract maths and concrete science (including the applied fields of engineering and technology) together we've pretty much covered everything, making STEM so large and all-encompassing that is a useless concept. You can't teach "STEM", but you can attempt to teach a few scientific concepts which can be applied to problems in engineering and/or technology. You can try the same with mathematics, except that you land yourself in the middle of another problem ....

And this next HUGE problem is the way most (non-mathematical) people think about mathematics, the big "M" in "STEM". Science (including engineering and technology) uses maths (small "m") like a tool, an aid to defining and solving problems and to build models. But this isn't really Maths (big "M"). Maths is based on logical reasoning, but there are differences between scientific reasoning and mathematical reasoning.
The scientific method is, broadly speaking, a form of deductive reasoning. A mathematical proof, the essence of maths, is largely based on inductive reasoning. The way "science" views the world is different to the way "maths" views the world. So why on earth do we lump "M" in with the "STE" ?
If I were a Maths teacher, I would be very concerned that lumping maths in with science, engineering and technology makes it look like maths is just a tool to be used rather than an elegant, logical, reasoning process.

I would make a similar argument for Science (S). Lumping science in with engineering and technology makes it look like science is just a tool to be used to solve engineering and technology problems. Science can be used this way, just like mathematics can be used as a tool, but this is not the most important aspect of science. Science is the systematic study of the structure and behaviour of "the world". Scientific study may lead to a theory or a model which can be used to make predictions, which can be tested, lending support to the theory or suggesting modifications to the theory, etc. It is the results of "science", the theory or model, that can be applied to problems (engineering and technology), but teaching/learning science should not be primarily about the application of results, it should be about understanding scientific concepts.

Let me just add that even within the science (S) part of STEM there are huge differences and difficulties. Chemists are primarily interested in understanding and making patterns with "atoms". Physicists are more interested in the interaction of energy and forces. A Chemist might analyse a rubbery material, then think about how atoms could be pushed around in the lab to make a similar material, or a different material with enhanced stretchiness compared to the original, or with less stretchiness, or the same stretchiness but a different colour, or different melting point, etc. A Physicist might look at the same material and be fascinated by the forces required to stretch the material, how far it can be stretched before it deforms or breaks, or whether its stretchiness depends on how fast or slow it is stretched or on how hot or cold it is, etc. Now you might be thinking that this would form a great basis for a STEM education (inquiry-based learning) activity, but I beg to differ. Indeed, students could probably competently and safely investigate stretchiness of a suitable material and think about how the material might be used (engineering/technology) but what have they learnt by doing this? They will have investigated one example (or maybe a few), and drawn a few conclusions about a specific material(s). But what is the point? Will they actually have any understanding of the chemistry and physics principles underlying their observations, because it is the scientific principles that are really useful, not the results of an isolated experiment or two.
In order to have an understanding of the material they need to understand how Chemists might analyse it, and they need to understand how structure and bonding effect properties. If they want to make a new material based on the structure of the original, then they are going to have to come to an understanding of reaction mechanisms. This in itself constitutes a lot of concepts before we even begin on the physics concepts they would need to understand stretchiness.

The problem with STEM education is that it over-emphasizes concrete application and under-emphasizes abstract reasoning. Mathematics and science are so much more than just "tools" to be applied to solve engineering and technology problems.
Mathematics (M) is based on logical reasoning.
Science (S) is based on logical reasoning.
What is engineering (E) based on? Engineering is the application of science and maths.
So what is technology (T) ? Technology is also the application of science.
So, STEM stands for Science (S), Mathematics (M) and their application (TE or should that be TA?).
I think a better acronym would therefore be S&M. I think students might find that more entertaining than STEM.

Thursday, September 7, 2017

Graphene from Graphite

In 2004, University of Manchester researchers isolated graphene by applying sticky tape to a piece of graphite and peeling off a layer, then repeating the sticking and peeling process on this and subsequent layers until they had a layer that was just one carbon atom thick. The final 2-dimensional layer of carbon atoms is graphene. The structure of graphene is shown below:

The researchers, Professors Andre Geim and Kostya Novoselov were awarded the 2010 Nobel Prize in Physics.

Graphene is a highly sought after material. It is stronger than steel, yet it is a million times thinner a strand of hair. It is also a better conductor than the copper commonly used for electrical wiring. In order to use graphene in consumer products it needs to be produced on a large scale and in commercial quantities. It is not commercially viable to spend large amounts of time peeling off layers from graphite using sticky tape to produce small quantities of graphene. So the race has been on to find a process that could be used commercially.

One method is to oxidize graphite using hazardous oxidizing agents like anhydrous sulfuric acid and potassium peroxide. A representation of a layer of this oxidized graphene from the stacked layers making up graphite is shown below:

Layers of oxidized graphene can then be separated chemically from the bulk graphite, but these processes take a long time, and, the product is not graphene but oxidized graphene which is not as conductive as pure graphene.

University of Connecticut (UConn) Professor Doug Adamson has found a new way to produce graphene based on its solubility. Graphene is insoluble in liquids like oil, hexane and water.
Imagine you have a jug containing some oil and some water. If you wait, the two liquids will separate out, forming two distinct layers as represented below:

The less dense oil will float on top of the more dense water. If you add graphite to the area where these two liquids meet (the interface), then the stacked layers of graphene sheets in the graphite spontaneously "unstack" and spread out to cover this interface. These trapped graphene sheets can be locked into place using a cross-linked polymer.

The researchers are now investigating how this graphene composite material could be used to desalinate brackish water.

Reference
  1. Steven J. Woltornist, Andrew J. Oyer, Jan-Michael Y. Carrillo, Andrey V. Dobrynin, Douglas H. Adamson. Conductive Thin Films of Pristine Graphene by Solvent Interface TrappingACS Nano, 2013; 7 (8): 7062 DOI: 10.1021/nn402371c

Further Reading:

Suggested Study Questions
  1. Explain why graphite is a good conductor of electricity.
  2. Explain how the structure of graphene and graphite are:
    • similar
    • different
  3. Explain why graphene is considered to be a 2-dimensional material but graphite is considered to be a 3-dimensional material.
  4. Explain why graphene is a much better conductor of electricity than graphite.
  5. What characteristics of graphene allow it to be peeled off in layers from bulk graphite. Explain your answer.
  6. Explain why a mixture of oil and water will separate out into 2 distinct layers rather than forming a homogeneous mixture.
  7. Consider the structure of graphene to explain the insolubility of graphene in:
    • water
    • oil
  8. Explain why copper is a good conductor of electricity.
  9. Discuss how the structures of copper and graphene are:
    • similar 
    • different
  10. Explain why graphene is a much better conductor of electricity than copper.

Monday, September 4, 2017

Formula for Hydrogen?

I admit it. I love TV game shows. Last Friday I watched one of my favourite shows while eating my (late) lunch. I was even moderately successful at answering some of the questions, until the Host asked The Chaser what the chemical formula for hydrogen was. This led to the following exchange:
Chaser: H
Host: Incorrect
Contestants: H one (we will assume they meant H1)
Host: Incorrect. The correct answer is H two (we will assume he meant H2)

So, who was right?

Let's take the Host's "correct" answer first.
The Earth's atmosphere contains small amounts of diatomic molecules of hydrogen gas. "Di" means two and "atomic" refers to atoms so hydrogen gas in the atmosphere is made up of molecules in which 2 atoms of hydrogen are bonded together. When we make hydrogen gas in the laboratory we are making these H2 molecules. So it seems that the Host got it right ..... except ..... the question didn't ask for the formula of hydrogen gas found in the atmosphere!

So let's turn our attention to the Contestants' response.
Is H1 a plausible chemical formula for hydrogen?
Not really. If there is only 1 atom of an element in the chemical formula, the "1" is trivial and not included in the formula, so H1 is the same as H which was the Chaser's response!

So, was the Chaser right?
Is H a valid chemical formula for hydrogen?
Hydrogen is a strange atom. It has 1 proton in its nucleus, and 1 electron "orbiting" that nucleus. In fact, this 1 so-called "valence electron" is a feature common to all Group 1 metals (alkali metals), but other properties of hydrogen suggest it is more like a non-metal than a metal. This similarity to the Group 1 metals led to the prediction that it should be possible to create metallic hydrogen. This would be a solid in which the hydrogen atoms (protons in effect) would be held in a 3-dimensional array with delocalised electrons acting as the metallic bonds holding the array together. This metallic hydrogen would, in theory, be an excellent conductor, indeed it would be a "superconductor", which is why the race has been on to create it!

A chemical formula of a covalent molecule tells us how many atoms of each element are covalently bonded together, H2 has 2 atoms of hydrogen with a covalent bond between them.
But the chemical formula for a 3-dimensional metallic array refers to the ratio of atoms of each element, if only 1 element is present in a metallic array, like that of sodium metal, then the chemical formula is just the symbol for the element, Na, in this case, or H if you are referring to metallic hydrogen.
So, H is a valid chemical formula for metallic hydrogen, if it exists.
But does metallic hydrogen exist?

In January 2017, researchers at Harvard University announced that they had produced metallic hydrogen in the laboratory using immense pressure. So metallic hydrogen, H, can exist.

Back to the game show.
The Host was right, H2 is the chemical formula for gaseous hydrogen in the atmosphere.
The Chaser was right, H is the chemical formula for metallic hydrogen.
The Contestants were almost right: Chemists don't write H1 they just write H.

There is a moral to this story.
Be careful when writing questions. The question should not be ambiguous unless you are prepared to accept multiple different answers that are correct.
Be even more careful when answering test and exam questions. If you need to make assumptions to answer the question you MUST state what those assumptions are when you write your answer.

Reference:
  1. Ranga P. Dias, Isaac F. Silvera. Observation of the Wigner-Huntington Transition to Metallic HydrogenScience, 2017 DOI: 10.1126/science.aal1579

Naming Covalent Compounds
Empirical Formula and Molecular Formula
Trends in Group 1 Elements
Metallic Bonding

Suggested Study Questions

  1. Use the Periodic Table of the Elements to find the chemical symbol for each of the following atoms:
    • hydrogen
    • helium
    • carbon
    • nitrogen
    • oxygen
    • chlorine
  2. Write a molecular formula for each of the following diatomic gas molecules:
    • hydrogen
    • nitrogen
    • oxygen
    • chlorine
  3. Give the number of atoms of each element present in the molecular formulae below:
    • H2O
    • H2O2
    • CO
    • CO2
    • NH3
    • NO
    • NO2
    • N2O2
  4. Let M represent an atom of an element. Circle the elements below for which the molecular formula of the element at room temperature and pressure could be represented by M
    • helium
    • sodium
    • oxygen
    • iron
    • gold
    • neon
    • chlorine
    • nitrogen
    • hydrogen
  5. For the description of each molecule below, write the molecular formula
    • one carbon atom and four hydrogen atoms
    • one nitrogen atom and three chlorine atoms
    • two nitrogen atoms and one oxygen atom
    • one nitrogen atom and five oxygen atoms
    • two chlorine atoms and two oxygen atoms
    • one carbon atom, one hydrogen atom and three chlorine atoms
  6. Given the name of each molecule below, write the molecular formula:
    • hydrogen chloride
    • carbon monoxide
    • carbon dioxide
    • sulfur dioxide
    • sulfur trioxide
    • sulfur dichloride
  7. Consider the list of compounds with a possible molecular formulae below. Circle the incorrect formulae and justify your answer:
    • water, 2HO
    • carbon monoxide, C1O1
    • hydrogen peroxide, H2O2
    • sulfur trioxide: SO2
    • ammonia, NH3
    • hydrogen sulfide, H2S
    • carbon dioxide, C2O
    • sulfur dichloride, S1Cl2
  8. From the list below, circle the elements that belong to Group 1 of the Periodic Table of the Elements:
    • sodium
    • helium
    • oxygen
    • lithium
    • chlorine
    • nitrogen
    • carbon
    • potassium
    • calcium
  9. Draw a table with the headings "metal" and "nonmetal". Place each of the following elements in the correct column:
    • hydrogen
    • helium
    • calcium
    • carbon
    • nitrogen 
    • potassium
    • oxygen
    • chlorine
    • sodium
  10. From the list below, circle the elements that would exist at room temperature and pressure as an array of "atoms" help together by delocalised electrons:
    • hydrogen
    • carbon
    • sodium
    • lithium
    • nitrogen
    • chlorine
    • iron
    • gold
    • oxygen



Thursday, August 31, 2017

Betaines

Betaines are found in plants, animals and microorganisms. Rich sources of betaines in the human diet are seafood, spinach and wheat germ or bran. Research is beginning to indicate that betaines are important nutrients for the prevention of chronic disease. Researchers are also interested in incorporating betaines into polymer brushes used for antifouling and lubrication.

Betaines are compounds with a positively charged functional group linked to a negatively charged functional group with an alkyl chain in between. The alkyl chain is often referred to as an alkyl chain spacer.  The general structure of an N-alkyl betaine is shown below:

The first betaine discovered was found in sugar beets in the nineteenth century. This betaine is (trimethylammonio)acetate, also known as trimethylglycine, and its skeletal structure is shown below:
Another example of a betaine is 2-(trimethylammonio)octadecanoate (also known as hexadecylbetaine) with the skeletal structure shown below:

2-(Trimethylammonio)tetradecanoate, or dodecylbutaine or laurylbutaine, is also a butaine and its skeletal structure is shown below:



Betaines are strongly attracted to water molecules because of these two charged functional groups.

The solubility of betaines in water is dependent on the length of the carbon chain, as well as on temperature and pH. 
In acidic solution, betaines acquire a net positive charge and act like a cationic surfactant. In anionic solutions, betaines acquire a net negative charge and act like an anionic surfactant.

Betaines can also be used in polymer brushes which are polymers bound to a surface. Polymer brushes can be used for antifouling and lubrication because the hydration of the ionic groups reduces the ability of other materials to adhere to the surface. 


Researchers at Kyushu University recently investigated a series of alkly chain spacers of different lengths bound to a silicon surface. They found that the polymer brushes swelled in humid air and water. It is believed that this is due to electrostatic repulsion between charged groups, and not dependent on the length of the alkyl chain.

In deionised water, net positive cations and net negative anions are repelled because of the  electrostatic force which causes the chain dimension to expand, whereas they shrink under high ionic strength by a charge screening effect of the bound ions.

Reference:
https://www.sciencedaily.com/releases/2017/08/170821094302.htm

Further Reading
Introduction to Functional Groups
2-Dimensional Structural Formula
Condensed Structural Formula
Molecular Formula
Amino Acids
Surfactants ( as found in synthetic detergents)
Intermolecular Forces and Solubility

Suggested Study Questions


  1. Locate and identify each functional group on the skeletal structural formula of
    • general formula N-alkyl betaine 
    • (trimethylammonio)acetate
    • 2-(trimethylammonio)octadecanoate
    • 2-(trimethylammonio)tetradecanoate
  2. Draw a 2-dimensional structural formula for each of the following molecules:
    • (trimethylammonio)acetate
    • 2-(trimethylammonio)octadecanoate
    • 2-(trimethylammonio)tetradecanoate
  3. Write the condensed structural formula for each of the following molecules:
    • (trimethylammonio)acetate
    • 2-(trimethylammonio)octadecanoate
    • 2-(trimethylammonio)tetradecanoate
  4. Write the molecular formula for each of the following molecules:
    • (trimethylammonio)acetate
    • 2-(trimethylammonio)octadecanoate
    • 2-(trimethylammonio)tetradecanoate
  5. Compare the structure of betaines to that of 2-amino acids. Can N-alkyl betaines be classified as alpha amino acids (2-amino acids) ? Justify your answer.
  6. Write chemical equations to describe what happens to an N-alkyl betaine in:
    • acidic aqueous solution
    • basic aqueous solution
  7. Compare the structure of N-alkyl betaines to the surfactants found in synthetic detergents. In what ways are surfactant molecules 
    • similar to N-alkyl betaines
    • different from N-alkyl betaines
  8. Explain how N-alkyl betaines act like 
    • a cationic surfactant in acidic aqueous solution
    • an anionic surfactant in basic aqueous solution
  9. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in water? Justify your answer.
  10. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in paraffin oil? Justify your answer.

Thursday, August 24, 2017

Nanoparticles to Remove Coral Bleaching Oxybenzone

Sunblocks contain a number of different compounds including oxybenzone which acts as a UV filter. The skeletal structural formula of oxybenzone is shown below:
Oxybenzone is soluble in water.
Before you go snorkeling in the Great Barrier Reef to be amazed by the beautiful corals, fascinating fish and other exciting wonders, you smother yourself in sunblock. When you step into the water, the oxybenzone starts to dissolve. Unfortunately, oxybenzone contributes to coral bleaching, the killing off of the tiny, colourful zooxanthellae marine algae that live inside corals. The result is that the coral loses its colour and appears white, as if it has been bleached.

Researchers have found a way to soak up the oxybenzone from the seawater using magnetite nanoparticles.

Magnetite, Fe3O4 , is a mineral made up of iron(II) and iron(III) oxides and is one of the main iron ores, that is, magnetite is mined in order to produce iron. Magnetite is ferromagnetic, that is, it is attracted to a magnet. It is the most magnetic naturally occurring mineral on Earth. If you could get the oxybenzone in the seawater to attach to magnetite nanoparticles then you could pull the oxybenzone out of the water using a magnet.

First, the researchers coated the magnetite nanoparticles with sodium oleate. The skeletal structural formula of sodium oleate is shown below:
Next, they oxidised the oleate coating to increase the number of hydroxyl (OH) functional groups:


Since oxybenzone can interact with other molecules via hydrogen bonds, magnetite nanoparticles  covered in a coating rich with hydroxyl functional groups increases the interactions between oxybenzone and the nanoparticles. Once the oxybenzone has hydrogen bonded to the nanoparticle coating, a magnet can be used to extract the particles from water.

Does it work?
One brave researcher applied sunblock, stepped into the ocean, waited 10 minutes, then collected a sample of the surrounding seawater. Back at the lab, chromatography was used to determine the concentration of oxybenzone in the water, 1.3 ppm. This is a disturbing result since it is known that the concentration needed to bleach coral is measured in parts per billion.
Next, the researchers prepared seawater samples. Some had no magnetite nanoparticles added, others had the nanoparticles added. Then they added 30 ppm oxybenzone to  all the samples. The concentration of oxybenzone in the samples with no nanoparticles did not change in an hour. In the samples that contained the nanoparticles, 95% of the  oxybenzone  was removed within the hour.

Reference
American Chemical Society. "Sopping up sunblock from oceans to save coral reefs." ScienceDaily. ScienceDaily, 21 August 2017.

Further Reading
Solutions Concepts
Water as a Solvent
Transition Metals (magnetism)
Fatty Acids
Carboxylic Acids
Nanoparticles and Nanotechnology
Parts per Million (ppm)
Chromatography
Experimental Design
Variables
2-Dimensional Structural Formula
Skeletal Structural Formula
Molecular Formula

Suggested Study Questions

  1. For a molecule of oxybenzone:
    • draw the 2-dimensional structural formula
    • give the molecular formula
  2. On the 2-dimensional structural formula of oxybenzone identify and name each functional group present.
  3. Use diagrams to explain why oxybenzone is soluble in water.
  4. Draw the 2-dimensional structural formula for oleic acid.
  5. On your structural formula of oleic acid, identify and name the functional group(s).
  6. Suggest a method by which you could change oleic acid into sodium oleate in the laboratory.
  7. Suggest a method by which you could oxidise sodium oleate in the laboratory.
  8. Explain the term "nanoparticle".
  9. Why do you think the researchers chose nanoparticles of magnetite rather than bulk magnetite for this research?
  10. Consider the description of the experiment used to determine the effectiveness of the magnetite nanoparticles in removing oxybenzone from seawater:
    • What was the hypothesis being tested?
    • What was the aim of the experiment?
    • What variables need to be considered in this experiment?
    • What is the independent variable in the experiment?
    • What is the dependent variable in the experiment?
    • Which variables are constant variables in the experiment?
    • Why did the experimenters add nanoparticles to some samples but not to others?
    • Write out a suitable method for this experiment.



Monday, August 21, 2017

Acenes

Acenes are molecules in which benzene rings, shown below, are fused together.
 
Researchers are very keen on making acenes because of their interesting properties.
Naphthalene, produced from the distillation of coal tar in the nineteenth century and traditionally used in mothballs, is a molecule in which 2 benzene rings are fused:
 Anthracene, a component of coal tar that is used to make dyes, has 3 fused benzene rings:

Tetracene (or naphthacene), is a semiconductor used to make organic light-emitting diodes (OLEDs) and organic field-transmitters (OFETs), has 4 fused benzene rings:

Pentacene is a semiconductor relevant to the building of photoelectronic devices. It oxidises when exposed to UV and visible light. It has 5 fused benzene rings:

The longer the acene molecule is, the less stable it is so the longer acenes are so unstable they do not occur in nature. Indeed, nonacene, in which 9 benzene rings are fused together was only detected recently, in 2010. Yet researchers are still interested in developing longer acenes because of their unique electronic properties.
In 2017, researchers from the Institute for Materials Science and Center for Advancing Electronics at Technische Universit├Ąt of Dresden (TUD) and the research center CiQUS (University of Santiago de Compostela) were able to make the elusive decacene in which 10 benzene rings are fused together.
Individual decacene molecules were visualised by high-resolution Scanning Tunneling Microscopy (STM):
The decacene molecule is so reactive that it had to be prepared on a gold surface under a high vacuum in order to stabilise it.

Reference
Technische Universit├Ąt Dresden. "Researchers obtain decacene, the largest acene synthesized ever." ScienceDaily. ScienceDaily, 14 August 2017. .

Further Reading

Suggested Study Questions:
  1. Draw the 2-dimensional structural formula for each of the following molecules:
    • benzene
    • naphthalene
    • anthracene
    • tetracene
    • pentacene
  2. Draw the condensed structural formula for each of the following molecules:
    • benzene
    • naphthalene
    • anthracene
    • tetracene
    • pentacene
  3. Give the molecular formula for each of the following molecules:
    • benzene
    • naphthalene
    • anthracene
    • tetracene
    • pentacene
  4. Give the empirical formula for each of the following molecules:
    • benzene
    • naphthalene
    • anthracene
    • tetracene
    • pentacene
  5. Name the following molecules found in the acene series:
    • 6 benzene rings fused together
    • 7 benzene rings fused together
    • 8 benzene rings fused together
    • 9 benzene rings fused together
  6. Consider the structure of the molecules in the acene series. Explain why Chemists use the term "fused" rather than "bonded" or "linked" to refer to how the benzene rings are joined together to make the acene molecules.
  7. Place the molecules in the acene series from benzene to decacene in order of increasing reactivity.
  8. What feature of the molecules in the acene series makes them useful semiconductors?
  9. Explain why the reactivity of the molecules in the acene series increases as the number of benzene rings fused together increases.
  10. Explain why decacene had to be prepared under a high vacuum.