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podcast transcript
It is a metal, part of the minerals that helped build empires, an ion that allows nerves to fire and muscles to move, and is found in the kitchen.
It has become one of the most common substances in kitchens around the world, helping to preserve food, shape trade routes, and advance industry.
However, when it is in its elemental form, it can literally explode.
Learn more about sodium in this episode of Everything Everywhere Daily.
Sodium is one of the most familiar chemical elements in everyday life, despite the fact that few people encounter it in its pure metallic form.
It is the element behind table salt, baking soda, sodium vapor lamps, lye water, various industrial chemicals, and the body’s most important electrical signals.
This is also a good example of how an element can react violently when left alone, but can be essential and harmless when combined in a common compound.
Sodium belongs to group 1 of the periodic table, has atomic number 11 and has one electron in its outermost shell. This lone valence electron is the key to almost everything about sodium’s behavior.
Because the outermost electrons are loosely held by the nucleus, sodium easily gives up electrons to form positively charged ions, achieving a stable electronic configuration.
This desire to lose electrons makes sodium highly reactive and a powerful reducing agent.
Pure sodium is a soft, silvery metal. It is soft enough to be cut with a knife. When freshly cut, the metal surface is shiny, but it quickly tarnishes in air as it reacts with oxygen and moisture.
The melting point of the metal is relatively low, around 97.8°C. This means that it dissolves just below the boiling point of water. Also, because it is less dense and lighter than water, the sodium pieces will float.
Its most famous property is its reaction with water. Sodium reacts with water to produce sodium hydroxide and hydrogen gas.
This reaction releases heat. Heat can ignite hydrogen gas, which is why sodium thrown into water can bubble, skate across the surface, catch fire, or even explode if enough hydrogen and heat builds up. This isn’t just a chemistry class stunt. This is a direct result of sodium’s desire to lose its outer electrons.
There are many videos online showing the reaction of sodium in water, which are pretty violent. All Group 1 elements behave this way; the heavier the element, the more reactive it becomes.
Sodium is not found naturally as a free metal because it is highly reactive. Instead, it is found in compounds, especially salts. The most important is sodium chloride (NaCl), which is common table salt.
Even though humans have been using sodium compounds for thousands of years, we had no idea that sodium was a thing or an element.
An important breakthrough occurred in 1807 when British chemist Humphrey Davy isolated sodium by electrolyzing molten sodium hydroxide.
By passing an electric current through molten compounds, he was able to break them down into their basic components. During the same period, he also isolated potassium, calcium, strontium, barium, and magnesium.
The name sodium comes from the Latin word ‘sodanum’, meaning a headache remedy made from a sodium-rich plant, and the chemical symbol Na comes from the Latin name ‘natrium’, which was used in some European languages and ultimately adopted as the official symbol.
Sodium is generally ranked as the sixth most abundant element in the earth’s crust, after oxygen, silicon, aluminum, iron, and calcium.
Sodium makes up approximately 2.3% to 2.8% of the Earth’s crust by weight, depending on source and estimate. Since it is not found in pure form, it also occurs in minerals such as feldspar, halite, and soda minerals, and in sodium ions dissolved in seawater.
Sodium chloride, also called table salt, is the most famous sodium compound, and I’ve already done an episode on this topic. But this is not the only important compound.
Sodium hydroxide, also called caustic soda or lye, is a strong base used in soap making, paper production, drain cleaners, and a variety of chemical processes.
Sodium carbonate, or soda ash, is used in glass making, detergents, and water treatment.
Sodium bicarbonate, or baking soda, is used in baking, as an antacid, in fire extinguishers, and for odor control.
Sodium hypochlorite is the active ingredient in many household bleaches.
Sodium nitrate has been used as a fertilizer and preservative. Sodium compounds are ubiquitous because sodium ions are stable, soluble, and easy to work with.
This is perhaps sodium’s greatest paradox. In its pure form it is very reactive and dangerous, but as an ion it is very stable.
In nature, sodium plays several roles. Geologically, it is part of the rock cycle and ocean chemistry. Sodium is weathered from rocks and transported through rivers, eventually accumulating in oceans, lakes, salt flats, and evaporative deposits.
In dry areas, sodium salts can accumulate in the soil, sometimes causing problems for agriculture by damaging soil structure and hindering plant growth.
Biologically, sodium is essential for animals. In humans and other animals, sodium ions help regulate fluid balance, blood volume, nerve impulses, and muscle contraction. Nerve cells use sodium and potassium gradients to generate electrical signals.
When a nerve impulse travels along a neuron, sodium channels open, sodium ions rush into the cell, and the electrical charge changes. This is one of the basic mechanisms that makes thought, sensation, movement, and heartbeat possible.
Sodium is also key to the body’s water balance. Where sodium goes, water tends to follow. This is why sodium affects blood pressure and fluid retention. The kidneys carefully regulate sodium levels, conserving sodium when intake is low and excreting sodium when intake is high. Hormones such as aldosterone help regulate this process.
Humans need sodium, but not in huge amounts. Too little sodium can cause hyponatremia, a dangerous condition in which sodium levels in the blood become too low. This can be caused by a serious illness, excessive water intake, certain medications, or extreme endurance exercise without adequate electrolyte replacement. Symptoms may include headaches, confusion, nausea, seizures, and in severe cases, death.
Consuming too much sodium, especially over a long period of time, is also a problem. High sodium intake has been linked to increased blood pressure in many people, and high blood pressure increases the risk of heart disease, stroke, and kidney disease.
The main source of excess sodium in the modern diet is generally not the salt shaker but rather processed foods, restaurant meals, processed meats, soups, sauces, snacks, and packaged foods.
Sodium is very important in industry. The biggest sodium-related industry is salt itself. Sodium chloride is mined from underground deposits, extracted from sea water, or produced from brine. Used in food, road deicing, soft water, animal feed and chemical manufacturing.
Salt is also the starting point of the chlor-alkali industry, which produces chlorine gas, hydrogen gas, and sodium hydroxide by electrolyzing salt water. These products are used in plastics, disinfectants, paper, textiles, detergents, pharmaceuticals and many other industries.
One of the most promising uses for sodium is as a coolant in certain nuclear reactors. Once melted, it is excellent at dissipating heat from the reactor core. This is commonly called a sodium cooled fast reactor (SFR). It is different from the typical water-cooled reactors used in most commercial nuclear power plants.
In a conventional nuclear reactor, water does two things. It carries heat away from the nucleus and slows down the neutrons. The slowed-down neutrons are called thermal neutrons, and they are very effective at sustaining nuclear fission, the kind of fuel currently used in most nuclear reactors.
In sodium-cooled fast reactors, the goals are different. Reactors are designed to use fast neutrons. That means neutrons that don’t slow down much. Sodium is useful because it conducts heat well but does not significantly dampen or slow down neutrons.
This allows the reactor to operate in the fast neutron spectrum. Fast reactors can make more complete use of uranium fuel and can potentially consume plutonium and other long-lived isotopes from spent nuclear fuel.
Sodium was also used in electric lighting.
A sodium vapor lamp is a gas discharge lamp that produces light by passing an electric current through sodium vapor. They are best known for their old yellow-orange street lights, which gave many roads, parking lots, tunnels and industrial areas their distinctive nighttime color.
There are two main types: low-pressure sodium and high-pressure sodium.
Low-pressure sodium lamps contain a discharge tube containing a small amount of metallic sodium and a starting gas such as neon or argon. When the lamp is first turned on, the starting gas will be red or pink in color. As the lamp warms up, the sodium vaporizes and the light turns a very strong yellow-orange color.
That weakness was also part of the strength. Low-pressure sodium lamps were very efficient. This product produces a lot of visible light per watt of power, making it ideal for street lighting, highways, security lighting, ports and industrial sites.
Sodium lamps began to be widely used for street lighting in the 1930s. This is mainly due to efficiency and the yellow light worked well even in fog.
High-pressure sodium lamps operate on the same basic principles but at higher pressures and temperatures. Because hot sodium is chemically aggressive and attacks ordinary glass, arc tubes are usually made of translucent alumina.
High-pressure sodium lamps often contain mercury and other substances that broaden the spectrum. The result is still yellow-orange, but not as bad as with low-pressure sodium lamps.
Sodium vapor lights were very popular in the 20th century, but have been rapidly disappearing over the past 20 years. The reason is actually very simple.
The yellow light from the lamp was acceptable because it was very power efficient. LED street lights, on the other hand, use much less energy, last longer, turn on instantly, work well with dimming and smart controls, and can provide more natural colors.
The transition from sodium vapor to LED street lights has dramatically changed the appearance of many cities at night. Aerial images of Chicago at night taken in the 1990s show a huge yellow grid. The photo I took today is a completely different color.
Finally, metallic sodium is useful for removing reactive elements such as oxygen, chlorine, sulfur, and other non-metals from compounds.
One special application is refining meth.
When titanium tetrachloride is exposed to metallic sodium, the sodium removes the chlorine, leaving only metallic titanium. Likewise, if you consume a type of metal oxide, such as iron oxide (aka rust), the sodium can strip the oxygen, leaving behind only pure metal and sodium oxide, also known as soda.
Sodium may not be rare, exotic or fancy, but it is one of the true building blocks of civilization. The oceans are full of it, our bodies need it, it’s found in our kitchens, and in the future it may be used in greater quantities in nuclear reactors.
However, there are problems with consuming too much or too little, and in its elemental form, the metal can be very dangerous.
All of this applies simultaneously due to the dual nature of sodium.
