Sodium is a soft, silvery-white metal classified as an alkali metal, a group of elements known for their intense chemical activity. Elemental sodium is highly reactive, which dictates how it must be handled and stored. Its reactivity is so pronounced that it is never found in nature as the pure metal, only in compounds like table salt.
The Atomic Reason Sodium is Highly Reactive
Sodium’s extreme reactivity can be traced back to its position as the first element in Group 1 of the periodic table, the alkali metals. A sodium atom has 11 electrons, with the electrons arranged in shells: two in the first, eight in the second, and a single electron occupying the outermost, or valence, shell. Atoms are most stable when their outermost shell is full, a configuration often referred to as an octet.
The most energetically favorable path for a sodium atom to achieve this stable configuration is to lose its single valence electron. By shedding this electron, the atom transforms into a positively charged sodium ion (Na+), which possesses a full outer shell of eight electrons, similar to the noble gas neon.
The energy required to remove this single, loosely held electron (known as the first ionization energy) is very low for sodium compared to most other elements. This low ionization energy means sodium readily gives up its valence electron, making it a powerful reducing agent and explaining its readiness to engage in chemical reactions. The resulting stable Na+ ion forms the basis of many common, unreactive compounds.
Demonstrations of Sodium’s Reactivity
Sodium’s atomic structure translates into vigorous chemical behavior when the metal is exposed to air or water. When a freshly cut piece of sodium is exposed to the atmosphere, its shiny surface rapidly tarnishes as it reacts with oxygen and moisture in the air. This surface reaction forms a layer of sodium oxide and sodium hydroxide, protecting the underlying metal only temporarily.
The most dramatic demonstration of sodium’s reactivity is its interaction with water, which is a highly exothermic process. When elemental sodium is dropped into water, it immediately reacts to produce sodium hydroxide and flammable hydrogen gas. The heat generated is often sufficient to ignite the hydrogen gas, resulting in a visible flame and sometimes a small explosion.
In stark contrast, when sodium is chemically bonded, such as in sodium chloride (table salt), the sodium ion (Na+) has already achieved its stable electron configuration, making the resulting compound completely unreactive with water.
How Elemental Sodium is Contained and Stored
Because elemental sodium is so eager to react with air and moisture, industrial and laboratory settings must employ special precautions to contain and store this highly reactive substance. The primary goal of storage is to prevent the sodium metal from coming into contact with water vapor, oxygen, or carbon dioxide in the atmosphere.
Pure sodium metal is typically stored submerged in a non-polar, inert liquid that excludes air and water. Common storage liquids include:
- Mineral oil
- Kerosene
- High-boiling petroleum distillates
These hydrocarbons do not react with the metal, and the liquid barrier prevents rapid corrosion or spontaneous combustion. For high purity applications, sodium may also be stored under an atmosphere of dry, inert gases such as argon or nitrogen.