:( Atomic volume cc / mol) 17.3
The content of elements in the sun: (ppm) 1000
Content elements in seawater: (ppm)
Pacific surface 0.00008
Nitrogen in the air density is 1.2572kg / m ^ 3, the density of ammonia is 1.2505kg / m ^ 3
Element name: Nitrogen
Element symbol: N
Crystal structure: unit cell is hexagonal unit cell.
Oxidation state: N-3, N-2, N-1, N + 1, N + 2, N + 3, N + 4, N + 5
Content of the crust: (ppm) 25
Bond energy: (kJ / mol)
N-H 390
N-N 160
N = N 415
N≡N (nitrogen) 948
N-Cl 193
N-C 286
N = C 615
N≡C 887
Cell parameters:
a = 386.1 pm
b = 386.1 pm
c = 626.5 pm
α = 90 °
β = 90 °
γ = 120 °
Sound propagation speed in which: (m / S)
353
Thermal conductivity: W / (m · K) 25.83
Ionization energy (kJ / mol)
M - M + 1402.3
M + - M2 + 2856.1
M2 + - M3 + 4578.0
M3 + - M4 + 7474.9
M4 + - M5 + 9440.0
M5 + - M6 + 53265.6
M6 + - M7 + 64358.7
Element types: non-metallic elements
Elements of atomic weight: 14.01
Proton: 7
Neutron: 7
Atomic number: 7
Respective period: 2
Number of affiliated group: VA
Electron shell distribution: L2-K5
Nitrogen is a colorless, odorless gas, the melting point of -209.86 ° C, the boiling point of -195.8 ° C, the gas density 1.25046 g / l, the critical temperature of -146.95 ° C, critical pressure of 33.54 atmospheres.
Nitrogen is the usual form of elemental nitrogen. It is colorless, odorless, very difficult to have a chemical reaction of the gas atoms. And it makes the flame goes out immediately.
preparation
Commonly used in industry cryogenic distillation of air way to separate nitrogen and oxygen. Industrial nitrogen are fitted with black cylinders.
PSA:
After the feed air compressor pressurized air through the primary filter processing into the cold and dry machine for drying, and then into the air reservoir through efficient oil filter, dry, clean and oil-free compressed air through the activated carbon adsorption tower first, then work into the two exchange adsorption tower, absorption tower equipped with high quality and efficiency of the carbon molecular sieve oxygen and nitrogen molecules due to the molecular sizes, under elevated pressure sieve preferentially adsorbs oxygen, after a period of time, molecular sieve adsorption of oxygen balance, according to the different carbon molecular sieve under pressure in the absorption amount of the different characteristics of gas, reducing the pressure to eliminate molecular sieve adsorption of oxygen, while the other adsorber boost to work through two adsorbers working alternately obtained continuous nitrogen
In addition to low temperature fractionation, but also in the industrial use of carbon molecular sieve (MSC) regeneration pressure (Pressure Swing Adsorption, PSA), to separate the low purity of nitrogen.
use
Cheap inert gas protection, protective atmosphere for simple metal refining and high-temperature synthesis of (its performance is less than helium and argon); high temperature for the synthesis of nitride (such as silicon nitride ceramics, boron nitride, etc.) . In addition it also compound also used in agriculture, such as nitrogen. Sometimes liquid nitrogen for cooling.
Oxide
Nitrogen oxides can form a variety.
In the oxide, nitrogen oxide number may range from +1 to +5.
Among the more important of NO and NO2.
The nature of nitrogen oxides in the following table:
Name Chemical Formula status colors and chemical properties Melting point (℃) Boiling point (℃)
Nitrous oxide, N2O gas colorless stable Note: that is, nitrous oxide -90.8 -88.5
NO colorless gaseous nitric oxide (solid, liquid when blue) -163.6 -151.8 moderate response capability
Dinitrogen trioxide N2O3 blue liquid at room temperature decomposition of NO and NO2 -102 -3.5 (decomposition)
Nitrogen dioxide NO2 gaseous red-brown strong oxidizing -11.2 21.2
Dinitrogen tetroxide N2O4 strongly colorless gaseous decomposition NO2 -92 21.3
Dinitrogen pentoxide unstable colorless solid N2O5 3047 (decomposition)

Oxidant (nitrite, dichromate, chlorine, bromine, water, heat CuO, etc.) oxidation of ammonia and ammonium nitrogen available. Commonly used laboratory heating saturated solution of sodium nitrite and ammonium chloride from the reaction:

NH4Cl + NaNO2- → N2 + 2H2O + NaCl

Ammonia can also be prepared by using a small amount of nitrogen Bromine:

8NH3 + 3Br2- → 4N2 + 6NH4Br

By the sodium azide (Sodium azida) NaN3 thermal decomposition can be obtained spectroscopically pure N2:

2NaN3 (s) - → 2Na (l) + 3N2 (g)

3.1.2 chemically reactive nitrogen

Nitrogen molecule is composed of two to three N atoms covalently combined (:N≡N:), the electronic structure of:

A σ bond present in the molecule, two π bond, i.e. triplet key (3-1)

3-1 N2 molecular structure diagram

The data shown in Table 3-2, it was found N≡N key length, high bond energy 946kJ · mol-1, to break this triple bond is not easy, especially in the third key demand higher energy (531kJ · mol-1). Therefore N2 than any other diatomic molecules are stable, no air, water, acid reaction, even just at 3273K 1% dissociation at room temperature. Nitrogen is therefore chemically inert material. Inert nitrogen is widely used as the inert media coverage on electronics, steel, glass industry, but also for light bulbs and inflatable rubber filler, for the protection of industrial oils, food protection, as a protective gas in precision experiments .

Table 3-2 nitrogen covalent bond with bond lengths

Active at high temperatures nitrogen enhancement, and some metal (Li, Mg, Ga, Al, B, etc.) to form a nitride:

N2 (g) + 3Mg (s) - → Mg3N2 (s)

Nitrogen and O2 at high temperatures (~ 2273K) or direct discharge conditions of synthesis of NO:

N2 + O2 → 2NO, ΔrG = 173kJ · mol-1

This is a method of nitrogen fixation. In recent years, it was experimentally confirmed that when lightning atmospheric nitrogen and oxygen combine to generate NO is converted to nitrate with the rain and then lowered to the ground for the plant use, is an important source of nitrogen in the soil.

The main purpose of nitrogen is ammonia, and thus the available fertilizer, nitrate, explosives, and other important chemical raw materials.

3.1.3 fixed nitrogen

Nitrogen is a chemical process in all living systems is an important element in deciding factor is food crops. Nitrogen in nature is inexhaustible. Air contains 80% of nitrogen, the nitrogen is difficult elemental state into useful compounds. Therefore, the nitrogen in the air into nitrogen-containing compound can be used, namely nitrogen fixation (Nitrogen fixation) is very concerned about the people issue.

Some algae and micro-organisms in nature, the protein has a special catalytic capabilities by means of a body - nitrogen-fixing bacteria (enzyme) plant can not use nitrogen in the air is converted to ammonia nitrogen can be used, such as legumes soybean, peanut and other rhizobia. Such biological nitrogen fixation to improve soil fertility and maintain nitrogen cycling in nature, save money and protect the environment has a very important significance.

For a long time, people used chemicals to explore the atmospheric nitrogen into nitrogen compounds that artificial nitrogen fixation. Artificial nitrogen fixation are generally three types: combustion air (arc method); oxygen, nitrogen direct synthesis of NO; ​​dicyanamide salt method, nitrogen and heated to 1073K CaC2 formed calcium cyanamide (CaCN2 or CaNCN):

N2 + CaC2- → CaCN2 + C

Nitrogen and hydrogen at elevated temperature and pressure conditions for direct ammonia catalyst:

N2 + 3H3 → 2NH3 △ rH = -46kJ · mol-1

The first two methods energy consumption is large, the current widespread use of nitrogen hydrogen ammonia method, but this method need to have high temperature and pressure synthesis conditions and the catalyst.

Artificial nitrogen fixation both energy consumption and production is limited, it is estimated that each year about 200 million tons of biological nitrogen fixation on the planet, equivalent to 4-5 times the world fertilizer production. Visible biological nitrogen fixation ability is extremely powerful. It has long been eager to use chemical methods simulate nitrogen-fixing bacteria, made of ammonia nitrogen to achieve under normal temperature and pressure fixed air. From the 1960s began to study chemistry simulation of biological nitrogen fixation, the study proved that nitrogenase enzyme (iron, iron - molybdenum protein) containing a transition metal and nitrogen molecules to form metal - nitrogen molecule complex. Such complexes are formed so that N2 molecule activation, easy to be produced by the reduction of ammonia. From 1965 the first synthetic nitrogen molecule ruthenium complex [Ru (NH3) 5N2] X2 (X = Cl-, Br-, I-,

Fe, Co, Ni, Ru, Rh, Ir, Pt, etc.) - N molecular complex. This demonstrates similar molecular nitrogen and CO can use its lone pair of electrons and bonded to the transition metal, a transition metal is formed - molecular nitrogen complex, these complexes are very easily reduced to N2 of ammonia, as a catalyst in the visible light excitation containing Ru aqueous solution (ⅱ) -N2 complex system, enabling N2 into ammonia.