Topics 2 & 12

Including International-mindedness, TOK, and 'Utilization' in Atomic structure

International-mindedness

1. International scientific cooperation under the ground at CERN

Scientific research and endeavour has a long history of crossing international boundaries. 200 years ago in October 1813, while Britain was at war with France, Sir Humphrey Davy accompanied by his wife and Michael Faraday travelled to France to collect a medal that he had been awarded by Napoleon Bonaparte for his work on electrochemistry. This spirit of international scientific cooperation continues today. CERN is funded by twenty European states but scientists from around the world use its facilities. Currently some 580 institutions and universities from around the world (representing 85 different countries) are using CERN’s facilities to research the atom.

2. International scientific cooperation above the Earth on the ISS

The first IB Higher Level Chemistry class I ever taught at Atlantic College in 1982 contained an 18 year old Canadian girl who could outdo the boys at everything. Grut as everyone called her, although her real name was Julie Payette, told me back then that she wanted to become an astronaut. She has subsequently served on two missions with NASA to the International Space Station. She calls herself now a ‘space engineer’ rather than an astronaut and as of 2017 become the Governor General of Canada. The International Space Station is not only involved in cutting edge research but also has a programme of activities involving the station which aims to educate and inspire high school students - this includes online activities. The station involves the cooperation of the United States, Japan, Russia and Canada together with ten European countries. In the microgravity environment of the station experiments are carried out by international scientists in biology, chemistry, physics, human biology, astronomy and meteorology.

Theory of Knowledge

Are the models and theories that scientists create accurate descriptions of the natural world or are they primarily useful interpretations for prediction, explanation and control of the natural world?

“Seeing is believing” – perhaps even though we know the limitations of this statement we will always question the nature of an atom as we will never be able to ‘see’ an atom in the traditional sense as all atoms are smaller than the wavelength of visible light. We can now (since 1981) ‘almost’ see them through the use of a technique known as scanning tunnel microscopy. Perhaps the reason why the Hadron Collider (a particle accelerator) receives such interest and financial support is mainly because of man’s search to know the ultimate truth. Atoms have come a long way from their original definition of being indivisible and by bombarding them with higher and higher amounts of energy more of their secrets are continually being unravelled.

1. The changing nature of the atom.

For the IB, students only really need to know that all atoms (apart from hydrogen) consist of just three sub-atomic particles (2.1.The nuclear atom). Protons and neutrons are located in a very small nucleus surrounded by electrons in energy levels and that atoms are essential empty space. Even so, I think it is useful to give them some of the historical background of how our understanding of atoms has changed over time. This can bring in a discussion of bias in chemistry as most text books credit the idea of an atom with the Greeks – in particular Democritus – dating back to 420 BCE. Because of the Silk Road, knowledge as well as goods travelled between Asia (via the Middle East) and the West. It seems probable that atoms were hypothesized even earlier by Eastern cultures but it is difficult to find irrefutable evidence. In a sense though, the concept of matter being composed of individual atoms was a completely hypothetical conjecture, as no hard scientific evidence was ever given to support the argument. Evidence was only forthcoming in the early nineteen century with John Dalton’s work on the combination of gases in fixed ratios. The later discovery of sub-atomic particles then leads to the ‘plum pudding’ model, then Rutherford’s nuclear atom to the Bohr Model.

Once quantum mechanics was established the Bohr model is superseded by the quantum model and from the work in CERN the nucleus is now continually being broken down into ever smaller sub-atomic particles with a plethora of names[1]. From a TOK point of view the atom provides a good example of how our knowledge is not fixed but continually changes over time.

2. The importance of spectroscopy in the way we ‘know’

If we return to the adage “Seeing is believing” then it is a sobering thought when we realise that we can only ‘see’ in a very narrow part of the electromagnetic spectrum (2.3.1) – the visible region. Much of chemistry relies of spectroscopy for its knowledge and this occurs in other regions of the spectrum, e.g., infra-red, ultra-violet and the radio region for nuclear magnetic resonance spectroscopy. Understanding how the brain works through functional magnetic resonance imaging, and determining the level of alcohol in the blood using an infra-red intoximeter are just two ways in which our understanding and knowledge of the world is totally dependent upon technology.

3. Making deductions from observation

The visible hydrogen spectrum (Balmer series) can be split into its discrete lines using a visible spectrometer and their wavelengths (λ) measured. Each line fits into an equation which is expressed as

1/λ = RH(1/4 - 1/n2)

Where RH represents a constant known as the Rydberg constant and n = 3,4,5,6,….

A mathematician might look at this and see it as a special form of a more general equation as ¼ is simply one over a number squared. The more general equation then becomes:

If we now change n1 from 2 (which gave us the visible series of lines) to 1 and calculate the wavelength of the lines it gives when n2 = 2,3,4,5… etc. we see that we get another series of lines but this time they lie in the ultraviolet region of the spectrum. It was this logic that made scientists look for this series which they found and called the Lyman series. To further support the argument the wavelength associated with the infinite level can be calculated. It is given when n1=1 and n2 = ∞ so the expression simply becomes:

1/λ = RH

Wavelength (λ) = velocity of light (c) divided by frequency (f) and Energy (E) is related to frequency (f) using Planck’s constant (h) by the expression E = hf.

Therefore E = hc/λ = hcRH

This is the energy involved in removing one electron from the lowest level (n = 1) to infinity (n = ∞) i.e. the energy required to ionize one hydrogen atom. If this is multiplied by Avogadro’s constant (L) it will give the value per mole. So the ionization energy of hydrogen can be calculated by simply multiplying together four of the best known constants in science.

E = hcRHL

This gives exactly the same value as the experimentally determined value (1312 kJ mol-1) which is a fantastic achievement for deductive reasoning.

Utilization

1. An example of a radioactive isotope used in diagnostic medicine

Radioactive isotopes are clearly harmful and great care has to be exercised when handling them but equally they are socially very useful. Commonly used isotopes in medicine include 60Co, 131I and 125I.


An interesting use of isotopes in medicine is MAG3 scanning to diagnose kidney problems. This technique was developed at the University of Utah, USA, in the 1980s and has in fact superseded the use of 131I. MAG3 scanning uses a metastable radioactive isotope of technetium, 99mTc. This is a gamma emitter with a half-life of six hours. This is long enough to use and follow in the body but short enough to do little invasive damage. The MAG refers to the ligand surrounding the technetium which is mercaptoacetyltriglycine [sometimes wrongly(?) called mercaptuacetyltriglycine]

The MAG3 is injected into the blood stream then the progress of the gamma emitting technetium is followed as it enters the kidneys and is finally excreted. It enables doctors to ‘image’ the kidneys and compare the functions of both kidneys. The patient is given a diuretic after the scanning is complete to excrete all the radioactive material. (The picture on the right shows a patient suffering from a pelvic urethra junction obstruction which stops the left kidney from excreting urine properly).
Other ways in which radionucleotides are used in medicine include Positron Emission Topography, otherwise known as a PET scan.

2. Drug detection

Students are introduced to a mass spectrometer in 2.1 The nuclear atom and later in 11.3 Spectroscopic identification of organic compounds where fragmentation patterns are included as an aid to structural identification. Mass spectrometry plays a major role in society. Modern mass spectrometers are incredibly sensitive and can analyse samples as small as 1 x 10-9 gram. They are routinely used in drug testing ranging from finding out what drugs someone who has overdosed has taken to testing athletes for cheating and testing members of the armed forces. Normally a blood or urine sample is taken and the components separated by gas chromatography. Each individual component is then passed through a mass spectrometer (GC/MS testing). The spectrometer can easily detect the amount of illegal drugs such as marijuana, cocaine, amphetamines, LSD, opiates and barbiturates in the body. It can also detect anabolic steroids which are commonly used by athletes to enhance performance. The technique works because each component breaks down to give a mass spectrum containing fragmentation patterns. These can then be compared with the spectra of known samples stored in the computer linked to the machine.

Footnotes

  1. ^ CERN, which is based in Geneva in Switzerland, has a fantastic visitor's centre and it is well worth taking your students there if you are at all able to.
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