Sodium’s symbol Na is from the Latin word natrium. The Romans did not know about free sodium metal as it does not exist in nature. Humphry Davy first isolated pure sodium metal in 1807. Natrium probably referred to one or more of the common salts of sodium metal, like table salt (sodium chloride, NaCl), or perhaps soda ash (sodium carbonate Na2CO3), baking soda (sodium bicarbonate, NaHCO3), or caustic soda (sodium hydroxide, NaOH). All of those chemicals are of immense importance in modern manufacturing and have also been used domestically for millenia.
Sodium metal is not much in demand. It is too hard to store as it reacts quickly with air to form an oxide and reacts explosively with water. Sodium is bound up in crustal rocks in a dizzying variety of minerals and is among the most abundant of all the terrestrial elements. It is the compounds of sodium that matter, particularly sodium chloride, as sodium ions (Na+) are essential to metabolism. The free sodium ions play a role in regulating blood volume, blood pressure, and blood pH.
When you discuss dietary sodium with your doctor you are really talking about your salt intake. Adult humans need about 500 mg per day. Dietary recommendations are for 1-2 grams per day but most Americans consume twice that. Salt is present in packaged foods and common preservatives include sodium benzoate, sodium nitrite, and monosodium glutamate. If you need to limit sodium you need to avoid prepared foods! Take a look at the sodium content of your groceries the next time you go shopping—you will find it an eye-opening experience. Too much sodium in the diet can lead to cardiovascular complications.
One interesting use of salt is in nuclear reactors. Molten sodium chloride can be used as a coolant. Its high temperature (700 Celsius) means it can more efficiently transfer heat from the reactor core to the boiler. Some reactors actually include the nuclear fuel as part of the molten salt mix! The technology is well-studied and has proven to work but has not been widely adopted. Interest in nuclear power as an alternative to carbon-based energy is increasing. Perhaps we’ll see a nuclear renaissance in the coming decades.
Sodium finds a use in sodium-vapor lamps. You’ve seen them in every parking lot and along every freeway. Like fluorescent lights they are efficient (about 100 lumens per watt) and long-lasting. Sodium light has a distinctive yellow color. A flame test with table salt or other sodium compounds will also give a yellow result.