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In situ availability: trace
Necessity: essential
Atomic number: 11
Atomic mass: 22.98977
group: 1
period: 3
normal phase: Solid
series: Alkali metals
density: 0.968 g/cm3
melting point: 370.87K,
boiling point: 1156K,
Ne ← Na → Mg
Atomic radius (pm): 180
Bohr radius (pm): 190
Covalent radius (pm): 154
Van der Waals radius (pm): 227
ionic radius (pm): (+1) 102
1st ion potential (eV): 5.14
Electron Configuration
2s2 2p6
Electrons Per Shell
2, 8, 1
Electronegativity: 0.93
Electron Affinity: 0.55
Oxidation states: 1
Magnetism: Paramagnetic
Crystal structure: Body centered cubic

Sodium is a Alkali metal in group 1. It has a Body centered cubic crystalline structure. This element has a stable isotope of 23

On the Moon NaK, a sodium potassium alloy, is one of the few substances that can be liquid in the ambient vacuum conditions for a considerable length of time. At the eutectic concentrations of Na & K the alloy stays liquid from -12 to over 700 Celsius. At the low temperature end the vapor pressure is low enough that the liquid takes a reasonable time to evaporate in the conditions Luna's outdoor environment. This liquid can be alloyed with a powdered addition of other metals at low temperature, perhaps making a Lunar Cement.

As an electrical conductor a cable made of sodium would need to have about three times the cross sectional area to have the same electrical conductivity as a cable made of copper. However, since copper is more than nine times as dense as sodium, the copper cable would be more than three times as heavy as the one made of sodium. Sodium might have been used as an electrical conductor on Earth if it did not have some undesirable properties. It is a fire hazard. It reacts with water to give off hydrogen which can explode. A chemical product of the reaction of sodium and water (lye) can cause chemical burns. Although these things are very inconvenient on Earth, there is no fire hazard, no explosion hazard, and no possibility of chemical burns when an electrical conductor made of sodium remains out of doors on Luna. One way of preventing such a cable from melting in the sun at 97.7 Celsius is to use it to conduct electricity in the polar area at the bottom of a zig zag ditch so the sun can never shine on the bottom of the ditch no matter what direction it shines from. In the equatorial regions of Luna, where daytime temperatures get higher than the melting point of sodium, an iron or aluminum pipe filled with sodium would make a good electrical conductor.

A considerable advantage of sodium over copper for use on Luna is the lack of available copper ore on Luna while there is some sodium which should be recoverable. Aluminum is much more plentiful still, but difficulty in extracting it from lunar soil could lead to sodium being available first. Calcium is also much more plentiful than sodium and is intermediate in conductivity between aluminum and sodium.

Sodium is available in lunar regolith in a concentration in the neighborhood of 0.2% by weight.