Sunday, 21 April 2013

Mercury: silver water

From Wikipedia
 Mercury's chemical symbol is Hg from hydrargyrum, 'silver water', derived from Greek. It's most well-known for being the only metal that's liquid at standard temperature and pressure (0 °C, 1 bar), and for being mistaken for an elixir of life by the first emperor of China.

Metallic bonding can be illustrated as a giant lattice of positive metal ions surrounded by a mobile sea of delocalised electrons. These delocalised electrons are responsible for many of metal's electrical conductivity, malleability and ductility: they carry charge, and allow the positive metal ions can slide over each other to be moulded or stretched into wire.
From BBC
Mercury has a low melting point because its valence electrons (bonding electrons) are not shared readily - the intermolecular bonds are weak and take very little energy to break. The electron sea is very thin, giving the metal poor electrical and thermal conductivity. Nevertheless, mercury's uniform expansion rate means it's good for going into thermometers.

Over thirteen times denser than water, mercury is a bioaccumulative toxin - once it gets in your body by inhalation, ingestion or absorption through the skin, it stays there and can build up over time. Mercury irreversibly inhibits selenoenzymes, which prevent and reverse oxidative damage to the brain and endocrine (hormone-secreting) organs, and symptoms of mercury poisoning include headaches, nausea, diarrhoea, vomiting and chromosomal damage.

Metal teeth fillings are amalgam, which is an alloy of 50% mercury. Amalgam fillings have not been proven to cause mercury poisoning, but some people have them replaced with composite or ceramic fillings for the placebo effect anyway. I've held a bottle of mercury - it was probably around 400ml? - and it is staggeringly heavy!

All this chemistry about mercury links rather nicely with the metallic trend. I know this post is called 'silver water', and it really is an attractive-looking substance, but for the love of life, don't drink it!

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