Sodium

Sodium has been an important element throughout human history, even though people didn’t know it by name for thousands of years. As far back as 6000 BCE, ancient civilizations discovered that salt (which is made of sodium and chlorine) could be used to preserve food. Before refrigerators existed, salt was one of the only ways to keep food from spoiling. Ancient Egyptians, for example, used salt to preserve fish and meat, which helped them store food for long periods. This simple mineral played a huge role in allowing early people to survive

Sodium wasn’t just valuable for food preservation—it was also considered a precious resource because of its role in salt. In ancient China, salt was so important that it was used as currency, and in the Roman Empire, soldiers were often paid in salt, which is where the word "salary" comes from. The trade of salt, rich in sodium, helped shape ancient trade routes, with salt caravans traveling across the Sahara Desert and sea salt being traded along the Mediterranean. Cities like Venice became wealthy due to their control over the salt trade.

Sodium remained a mystery for a long time, even though salt was essential to life. In 1807, British chemist Sir Humphry Davy made a major breakthrough when he became the first person to isolate sodium from salt. Using a process called electrolysis, where electricity is passed through a substance to break it down, Davy was able to separate sodium from the chlorine in salt. This was a huge discovery because it helped scientists better understand the chemical makeup of salt and the elements within it. Davy’s work with electrolysis didn’t just stop with sodium; he went on to isolate several other elements as well.

Throughout history, people fought over salt, and by extension, sodium, because it was so valuable. Salt became a source of conflict, as governments placed heavy taxes on it. In Europe, salt was so expensive that it led to wars and revolts. In France, the government’s control over and high taxation of salt led to protests and was one of the many issues that contributed to the French Revolution. In India, one of the key moments in the country’s fight for independence was the Salt March, led by Mahatma Gandhi, in protest of British taxes on salt.

Today, sodium is easy to find in many forms, but its role in salt has shaped human history for thousands of years. Whether preserving food or driving major historical events, sodium has had a huge impact on the world.

Sodium, like every reactive element, is never found free in nature. When isolated, however, it is a bright, silvery metal with a density just below that of water. So, it (barely) floats, but it also reacts violently in water. It is the third-least-dense elemental metal after lithium and potassium. It is a good conductor of heat and electricity. And the metal is soft enough to be cut with a knife quite easily.

Metallic sodium is vital in the preparation of various compounds in organic chemistry. The metal can also be used to improve the structure of certain alloys, descale metal, and purify molten metals.

Liquid sodium metal can be used as a coolant in certain nuclear reactors because it has excellent heat-transfer properties. It circulates in pipes through the reactor, absorbing heat from the nuclear reactions and bringing that heat to a boiler to make steam. The steam drives a turbine to make electricity. Sodium can also be alloyed with potassium (NaK) to make a metal that remains liquid at room temperature so the metal doesn’t harden in the pipes when the reactor is off.

The light emitted by sodium atoms includes two very prominent wavelengths, both yellow. Familiar yellow streetlights are sodium lamps. And yellow sodium lasers are used in adaptive optics at major astronomical observatories. The laser beam is pointed at the astronomical target, and a system rapidly analyzes changing atmospheric distortions to the beam. The system then makes minute adjustments to the shape of the telescope mirror to compensate, leading to sharper images.

However, sodium metal is far less useful than its compounds. Millions of tons of salt and other sodium compounds are produced each year. Salt is used for de-icing, in addition to food flavoring and preserving. Sodium carbonate is a used as a water softener. And sodium bicarbonate, or baking soda, is used in, well, baking. These and other sodium compounds are important to the paper, glass, soap, textile, petroleum, chemical, and metal industries. Soap, for example, is generally a sodium salt of certain fatty acids.

Sodium is the sixth-most-abundant element in the crust of the earth. It is most commonly found in the form of sodium chloride. This salt (ordinary table salt) dissolves easily in water and has therefore been absorbed into the oceans over time. Salt can also be found in many dried seabeds and lakebeds.

Sodium metal is obtained commercially by the electrolysis of sodium chloride.