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June 10, 2012

Sodium is an all round bloody nice chap. Cheerful, outgoing, up for almost anything and doing lots of really important things without bragging about it. It is very similar to lithium (unsurprising as it is directly beneath it in the periodic table and therefore part of the same Alkali Metal family) but without the desperate attention seeking ego. Like lithium sodium is keen to get rid of the one electron in its outermost shell to make it appear like stable boring neon. Being so keen to shed an electron it reacts with many things and is always found on Earth as Na+ in compounds.

The name sodium originates from the Arabic suda meaning headache as sodium carbonate was known to alleviate headaches. The name continued in various guises until the element sodium (meaning of soda) was isolated from sodium hydroxide (caustic soda) in 1807 by Sir Humphrey Davy (one of the fathers of modern chemistry, brilliant lecturer, he also invented an important lamp). So why the chemical symbol Na? Well that was decided by Jons Jakob Berzelius as a contraction of natrium, the Latin version of the Egyptian word natron (a natural mineral salt containing mostly sodium carbonate). 

Sodium burning

As an element sodium is a soft shiny metal that can be cut with a knife. It is not a very dense metal so floats on water but most people are distracted from this observation by the rather dramatic reaction the metal has with water. It burns, spits and skates around like a cartoon character with its hair on fire. The flame produced is a characteristic bright orange colour which has lead to sodium’s use in fireworks and street lighting (the sodium in the light is sealed up in an inert atmosphere inside a glass tube which is why the lights don’t explode when it rains). Apart from specialist uses in chemistry labs sodium metal’s main application is as a coolant in some nuclear reactors. Sodium melts at 97 degrees Celsius and with a high thermal heat capacity  and so is a very effective way of controlling the heat from a reactor core.

Sodium is one of 27 elements essential for human health (and any other animal for that matter). We have around 100g of sodium in our body and need to supplement this with about half a gram a day from our diet. Obviously we don’t snack on sticks of sodium metal as it would explode in our mouths. The usual form of sodium we ingest is as salt (sodium chloride) and the importance of this commodity has been recognised for millennia.  The word salary comes from the Latin salarium, the salt wafers given to Roman soldiers as part of their pay. So why is sodium so important to us?

Sodium controls our blood pressure, osmotic equilibrium and pH. But more interestingly it is used to send nerve signals and thereby makes all our muscles move. In our bodies Na+ travels through sodium channels to the interior of nerve cells. This makes the cell positively charged  and so a potassium ion K+ is pushed out of the cell to redress the balance. The difference between having Na+ or K+ inside the cell creates a tiny electrical signal which travels down the axon section of neurons. All of this works fine unless the sodium channels get blocked for some reason.

One reason sodium channels can be blocked is if you have eaten tetrodotoxin, a poison found in pufferfish. This is less strange than it may sound as the Japanese a very fond of pufferfish sushi or ‘fugu’. Sushi chefs have to train for years to prepare fugu safely. One of the tests the chefs go through is to eat their own preparation of the pufferfish meat. Apparently there is a 65% failure rate and no antidote to the toxin. The best fugu is said to contain just enough  toxin to make your lips and tongue tingle (and the mind boggle).

There is also speculation that dried pufferfish may be the active ingredient in Haitian zombie powders. People who have eaten pufferfish toxin certainly appear dead as all their muscles stop working, even those that control breathing. In Japan this means that anyone suspected of fugu poisoning is laid next to their coffin until there are obvious signs of decay rather than bury someone alive. There is a lot more to zombie stories than shuffling corpses crying out “Brains!”. And you thought Hollywood just made stuff up.

Next time it magnesium, not to be confused with manganese which is totally different.


Images by @SciCommStudios

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