Nitrogen

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Nitrogen discharge tube.

Nitrogen is a chemical element with symbol N and atomic number 7. Nitrogen is a common element in the universe, estimated at about seventh in total abundance in our galaxy and the Solar System. On Earth, the element is primarily found as the gas molecule; it forms about 78% of Earth's atmosphere. The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772.

Properties

Chemical

Nitrogen is a nonmetal, with an electronegativity of 3.04. It has five electrons in its outer shell and is, therefore, trivalent in most compounds. The triple bond in molecular nitrogen (N2) is one of the strongest. The resulting difficulty of converting nitrogen into other compounds, and the ease (and associated high energy release) of converting nitrogen compounds into elemental N2, have dominated the role of nitrogen in both nature and human economic activities.

While nitrogen is relative inert, certain metals such as magnesium or lithium will burn in a nitrogen atmosphere.

Physical

At room temperature, nitrogen is a colorless and odorless gas. At atmospheric pressure, molecular nitrogen condenses (liquefies) at 77 K (−195.79 °C) and freezes at 63 K (−210.01 °C) into the beta hexagonal close-packed crystal allotropic form. Below 35.4 K (−237.6 °C) nitrogen assumes the cubic crystal allotropic form (called the alpha phase). Liquid nitrogen, a fluid resembling water in appearance, but with 80.8% of the density (the density of liquid nitrogen at its boiling point is 0.808 g/mL), is a common cryogen.

Availability

Nitrogen cylinders can be bought at hardware stores and welding supply stores. Liquid nitrogen can be bought from chemical suppliers, and while it's not expensive, the container used for storage, Dewar, is.

Preparation

Nitrogen can be isolated from air via reduction of oxygen with copper turning or other reducing agents (except metals that will burn in a nitrogen atmosphere, such as lithium, magnesium or titanium). The purified gas will contain ~1% argon. Smaller, but purer amounts of nitrogen can also be obtained by decomposing sodium azide. Nitrous oxide can also be used.

Liquid nitrogen can be made at home, by employing an air compressor and a cooling installation. A good tutorial can be found here.

Projects

  • Cooling baths (liquid nitrogen)
  • Haber process (small scale)
  • Make lithium nitride
  • Inert atmosphere

Handling

Safety

Gaseous nitrogen is inert, but in an enclosed space at high concentrations can displace oxygen, and therefore presents an asphyxiation hazard.

Direct skin contact with liquid nitrogen will cause severe frostbite (cryogenic "burns"), either instantly or a second or more after direct exposure, depending on the form of liquid nitrogen.

Storage

Compressed nitrogen tanks should be stored away from any heat sources. Liquid nitrogen dewars should be kept away from any source of heat and light and MUST have a pressure release valve to prevent a pressure build-up. The valve must be checked from time to time for any problems.

Disposal

Nitrogen can be safely released in atmosphere. Avoid doing this in a closed chamber.

References

Relevant Sciencemadness threads