Monday, 11 March 2013

The Name's Bond. Atomic Bond

That's not a song title, is it?  Ah well.

Two videos today.  Here's one:

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Antibiotic resistance is a growing problem, to the extent that in a couple of decades it's likely to become impractical to do things which increase the risk of infection safely, like treat cancer and transplant organs, or even carry out hip replacements, because of the risk of infection from bacteria such as Klebsiella, E. coli O157 and MRSA.  This is because bacteria evolve resistance to antibiotics.

There are a number of possible answers to this.  One is to use more complex mixtures to deal with infections, for instance herbal remedies and essential oils.  Echinacea would be one example, though i'm not keen.  Herbal remedies and essential oils which are antibacterial usually contain a wide variety of different compounds which address the issue in different ways.  Resistance to one of those compounds is unlikely to work against another, and as a result, bacteria are unlikely to evolve resistance.  The hundreds of millions of years over which plant and other resistance to infection has evolved means that it is a tested and reliable technique to avoid infection.

A second approach is bacteriophage therapy.  Viruses exist which kill bacteria by injecting their DNA into them and, as is usual with viruses, use the cells' machinery to replicate themselves at a cost to the cell, in this case the death of the bacterial cell.  Again, resistance does not develop to these because they are locked in an evolutionary arms race.

Apart from these possibilities, bacteria can be prevented from infecting by increasing the body's mechanical resistance to their incursion, for instance by increasing the strength of mucous membranes and maintaining outward flow of fluids such as urine, tears and sweat.

Finally, the variety of drugs developed by the pharmaceutical industry is usually very narrow and the same applies to antibiotics.  Many antibiotics are modelled on fungal compounds, and while these are effective at killing a wide variety of bacteria, they are less effective at killing other fungi and as a result the ecosystem of the body undergoes invasion from fungi such as thrush when they are used.  A whole world of variety exists out there which has yet to be exploited.

And this one:

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A rather cynical and jaded video about the characteristics of different types of chemical bond for GCSE Chemistry.

Ionic bonds are between positively and negatively charged ions such as in sodium chloride (table salt).  When an electron shell is close to empty or full, it avidly seeks electrons to redress the energy state of its outermost orbital.  Examples are found among the halogens and alkali metals, such as sodium, potassium, chlorine and fluorine.  Ionic compounds are not really made of molecules but are instead atoms of elements closely bonded to each other.  Because their bonds are strong, they have high melting points and tend to be solid at room temperature.  They are readily soluble in water, forming solutions which conduct electricity, but are good insulators.  One of the elements in an ionic compound is a metal and one a non-metal.

Covalent compounds share electrons, examples being water and carbon dioxide.  They form between non-metallic elements.  They form real molecules between which the bonds are weak, and so they have lower melting points than ionic compounds.  Their solutions do not conduct electricity and they are relatively insoluble.

Metallic bonds are where electrons become delocalised and as a result they confer various distinctive properties on metals:  lustre, malleability, sonorousness and hardness.

I also cover allotropy in this.  Graphite and diamond are two allotropes of carbon.  Graphite consists of sheets of hexagonal arrangements of atoms which are strongly bonded within the sheets but not between them.  It conducts electricity fairly well because of the straight routes along which electrons can move.  Diamond, on the other hand, is tetrahedrally arranged and therefore very hard but does not conduct electricity well.

Other examples of allotropy are red and white phosphorus.

The first one was done in a tearing hurry, hence the bits of paper rather than slideshow-type inserts.  If i'd edited them in, it would've taken too long.  The second one was a bit more finessed, except that the whole over-simplification thing is really doing me 'ead in.  I also think i might have got some things honestly wrong.

A few pics from the second vid:

Nice picture of sodium fluoride from Wikipedia.

Graphite.  Made me think of buckyballs and nanotubes.

Two allotropes of phosphorus, which has oddly and coincidentally turned out to look like the Becoming YouTube thumbnails.