Nitrogen is a chemical elementChemical symbolYes N, itsAtomic numberIt is 7.Nitrogen is the most important element in the air. It exists widely in nature and plays an important role in organisms. It is one of the basic elements of amino acids.
Nitrogen and its compounds are widely used in production and life.
In 1772, Swedish pharmacistsScheele Andrutherford[6-7]They were independently discovered by French scientistsLavoisierDetermination is an element.
In 1787, Lavoisier and other French scientists put forward the English name of nitrogen, which is“SaltpeterChinese chemists at the end of the Qing DynastyXu ShouWhen nitrogen was first translated into Chinese, it was written as "light gas", meaning that it "diluted" the oxygen in the air.
The element name comes from Greek, which originally means "saltpeter".
Content distribution
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The content of nitrogen in the earth's crust is very small. Most of nitrogen in nature exists in the atmosphere in the form of simple molecular nitrogen, which accounts for 78% of the air volume.The most important mineral of nitrogen is nitrate.[1]
The weight percentage of nitrogen in the crust is 0.0046%, and the total amount is about 4 × 10twelveTons.Proteins in plants and animals contain nitrogen.Nitrate in soil, such as KNOthree。In South America, Chile has saltpeter ore (NaNOthree）This is the only such mineral deposit in the world, a rare nitrogen bearing mineral deposit.[2]Nitrogen containing molecules, such as NH, have been found in interstellar spacethree、HCN, etc.
isotope
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Z(p)
N(n)
Mass (u)
half life
Nucleus
spin
Relative abundance
Variation of relative abundance
seven
three
10.04165(43)
200(140)×10s
[2.3(16) MeV]
(2-)
seven
four
11.02609(5)
590(210)×10s
[1.58(+75-52) MeV]
1/2+
6.90(80)×10s
1/2-
seven
five
12.0186132(11)
11.000(16) ms
1+
seven
six
13.00573861(29)
9.965(4) min
1/2-
seven
seven
14.0030740048(6)
stable
1+
zero point nine nine six three six
(20)
0.99579-0.99654
seven
eight
15.0001088982(7)
stable
1/2-
zero point zero zero three six four
(20)
0.00346-0.00421
seven
nine
16.0061017(28)
7.13(2) s
2-
seven
ten
17.008450(16)
4.173(4) s
1/2-
seven
eleven
18.014079(20)
622(9) ms
1-
seven
twelve
19.017029(18)
271(8) ms
(1/2)-
seven
thirteen
20.02337(6)
130(7) ms
seven
fourteen
21.02711(10)
87(6) ms
1/2-#
seven
fifteen
22.03439(21)
13.9(14) ms
seven
sixteen
23.04122(32)#
14.5(24) ms
[14.1(+12-15) ms]
1/2-#
seven
seventeen
24.05104(43)#
seven
eighteen
25.06066(54)#
1/2-#
Physical and chemical properties
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physical property
The most important mineral of nitrogen is nitrate.There are two natural isotopes of nitrogen: nitrogen-14 and nitrogen-15abundance99.625%.
Crystal structure: the unit cell is hexagonal unit cell.
Element type: non-metallic element
Nitrogen is a colorless and odorless gas.The usual simple form of nitrogen isnitrogen。It is colorless, tasteless and odorless. It is not easy to have chemical reactions and is chemically inert. Moreover, it does not support combustion and is slightly soluble in water and ethanol.For synthetic ammonianitric acid, used as material protection agent and refrigerant.
CAS No
7727-37-9。
Melting point (℃)
-209.8
Boiling point (℃)
-195.6
Relative vapor density (air=1)
zero point nine seven
Saturated vapor pressure (kPa)
1026.42(-173℃)
Critical temperature (℃)
-147
Critical pressure (MPa)
three point four zero
Atomic volume: (cmthree/mol)
seventeen point three
Element content in the sun (ppm)
one thousand
Pacific surface
zero point zero zero zero zero eight
Oxidized state
-3，-2，-1，0，+1，+2，+3，+4，+5
Relative atomic mass
fourteen point zero zero six seven
Period
two
Number of families
V A
chemical property
The valence electron layer structure of N atom is 2stwo2pthree, that is, there are three single electrons and a pair of lone electrons. On this basis, the following three bond types can be generated when forming compounds:
N atom has higher electronegativity (3.04), which is the same as that of metal with lower electronegativity, such as Li (electronegativity 0.98)Ca (electronegativity 1.00)When Mg (electronegativity 1.31) and the like form binary nitride, 3 electrons can be obtained to form N3-Ions.
N3-The anion has a high negative charge and a large radius (171pm). It will be strongly hydrolyzed when encountering water molecules, so the ionic compounds can only exist in the dry state, without N3-Hydrated ions of.
When N atoms form compounds with nonmetals with high electronegativity, the following covalent bonds are formed:
⑴ N atom adopts spthreeHybrid state, form three covalent bonds, retain a pair of lone electron pairs, and the molecular configuration is triangular cone, such as NHthree、NFthree、NClthreeEtc.
If four covalent single bonds are formed, the molecular configuration is tetrahedral, such as NHfour+Ions.
⑵ N atom adopts sptwoHybrid state, forming two covalent double bonds and one single bond, and retaining a pair of lone electron pairs. The molecular configuration is angular, such as Cl-N=O.(N atom and Cl atom form a σ bond and a π bond,A pair of lone electrons on the N atom makes the molecule angular.)
If there is no lone electron pair, the molecular configuration is triangular, such as HNOthreeMolecule or NOthree-Ions.The N atom in the nitric acid molecule forms three σ bonds with three O atoms respectively, and a pair of electrons on its π orbital and the single π electrons of two O atoms form an indefinite π bond with three centers and four electrons.In nitrate ion, an indefinite region of four center six electrons is formed between three O atoms and central N atomsLarge π bond。
With this structure, the apparent oxidation number of N atom in nitric acid is+5. Nitrate is stable enough under normal conditions due to the existence of large π bond.
⑶ N atom adopts sp hybridization to form a covalent triple bond, and retains a pair of lone electron pairs. The molecular configuration is linear, such as NtwoMolecule and CN-The structure of N atom in.[3]
When N atoms form simple substances or compounds, they often retain lone electron pairs, so such simple substances or compounds can be used as electron pair donors to coordinate with metal ions.For example, [Cu (NHthree)four]2+。
Nitrogen mainly exists in the atmosphere in the form of diatomic molecules in nature, so it is obtained by fractionation of liquid air in industry.The product is usually stored in steel cylinders for sale.The purity of nitrogen obtained from air fractionation is about 99%[4], which contains a small amount of oxygen, argon, water and other impurities.
Nitrogen can be obtained by fractionating liquid air:
Fractionated liquid air for industrial use (boiling point Ntwo=62.93K，Otwo=90K，Ar=83K），"Common nitrogen" with purity of 99% can be obtained (the remaining 1% is OtwoAnd noble gases).High purity nitrogen with 99.9% electron density was obtained by ordinary nitrogen purification.
There are many ways to prepare a small amount of nitrogen in the laboratory.For example, solidAmmonium nitriteTo produce nitrogen:
This reaction is violent and difficult to control.Therefore, it is often used in saturated sodium nitrite solutionammonium chlorideSolution, or directly warm the saturated ammonium nitrite solution to obtain nitrogen.The nitrogen thus produced contains a small amount of impurities such as ammonia, nitric oxide, oxygen and water.
Ammonium dichromate thermal decomposition can also produce nitrogen:
The above reaction is explosive, but it can be controlled if sulfate is added:
Nitrogen can also be prepared by introducing ammonia into bromine water.After purifying and removing a small amount of ammonia, bromine, water and other impurities, relatively pure nitrogen can be obtained:
Chlorine can also oxidize ammonia to generate nitrogen:
Spectrally pure nitrogen can be prepared by carefully heating very dry barium azide or sodium azide (the reaction is intense, pay attention to temperature control, and add slow release agent):
application area
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Industrial applications
The inertia of nitrogen is widely used in electronics, steel, glass, as well as filling materials for light bulbs and expansion rubber. It is used in industry to protect oil, grain, and as a protective gas in precision experiments.
At room temperature, nitrogen can be directly combined with many compounds, such as LiMg, Ca, Al, B, etc., react to generate nitridation:
NtwoAnd OtwoDirect combination under high temperature (~2273K) or discharge conditions
This is a method of fixing nitrogen. It is estimated that 400 million to 500 million tons of nitrogen compounds are synthesized by lightning every year on the earth, while about 100 million tons are artificially synthesized.
Physiological function
Nitrogen is one of the essential nutrients for plant growth. It is a component of every living cell.Plants need a lot of nitrogen.
Nitrogen is a component of chlorophyll,Chlorophyll-aandChlorophyll bThey are all nitrogenous compounds.Green plants carry out photosynthesis to convert light energy into chemical energy, and convert inorganic matter (carbon dioxide and water) into organic matter (glucose) by means of chlorophyll.Glucose is the raw material for plants to synthesize various organic substances, while chlorophyll is the factory for plant leaves to produce "food".Nitrogen is also a component of the vitamin and energy system in plants.
The effect of nitrogen on plant growth and development is very obvious.When nitrogen is sufficient, plants can synthesize more proteins to promote cell division and growth, so the leaf area of plants increases rapidly, and more leaf area can be used for photosynthesis.
In addition, the abundance and deficiency of nitrogen are closely related to the content of chlorophyll in leaves.It can judge the supply of nitrogen nutrition from the size of leaf area and leaf color.In the seedling stage, nitrogen deficiency of general plants is often characterized by slow growth, short plants, thin and small leaves, and yellow leaves.Gramineae crops show less division.In the late growth period, when nitrogen was seriously deficient, the spike was short and the grain was not full.After increasing nitrogen fertilizer, it has obvious effect on promoting plant growth.Often after application, the leaf color turns green quickly and the growth increases.However, the amount of nitrogen fertilizer should not be too much. When nitrogen is applied too much, the amount of chlorophyll increases, which can make the leaves stay green for a longer time, so that there is a trend of prolonging the growth period and green and late maturing.For some root and tuber crops, such as sugar beet, when nitrogen is too much, sometimes the growth of leaves is significantly increased, but the yield of tubers with economic value is disappointing.[5]
Element fixed
Since nitrogen is an important fertilizer, the method of transforming nitrogen into nitrogen compounds is calledNitrogen fixation。It is mainly used in agriculture.It is divided into biological, natural and artificial nitrogen fixation.
One way to fix nitrogen is to use plant rhizobia. Rhizobia is a kind of bacteria, which can make the roots of leguminous plants form nodules. Under natural conditions, it can convert nitrogen in the air into nitrogen compounds for plant use.This is the truth of the saying: "beans can not be fattened, and the fields will be fatter after several years of continuous planting".[3]
Impact on plants
Nitrogen is the main component of protein, plays an important role in the growth of stem and leaf and the development of fruit, and is the nutrient element most closely related to yield.Before the first ear fruit expanded rapidly, the nitrogen absorption of the plant gradually increased.
Later, in the whole growth period, especially in the peak fruiting period, the absorption reached the peak.When the soil is deficient in nitrogen, the plant is short, the leaves are yellow, the flower bud differentiation is delayed, the number of flower buds is reduced, the fruit is small, the fruit setting is little or no, the yield is low, and the quality is poor.When too much nitrogen is applied, the plants will grow excessively and flourish, which will easily cause a lot of falling flowers, stagnate fruit development, reduce sugar content, and weaken the disease resistance of plants.Tomatoes need nitrogen fertilizer, which is indispensable in seedling stage. Proper control is required to prevent overgrowth;During the fruit bearing period, frequent application should be made to ensure the need for fruit development.
Nitrogen is a component of green leaf element synthesis. Chlorophyll a and Chlorophyll b contain nitrogen compounds.Chlorophyll is the plant that makes carbohydrates.Nitrogen can synthesize proteins and promote cell division and growth.[5]
Nutrient balance
Proteins are decomposed into amino acids and small molecular peptides in the digestive tract and absorbed. Most of them are used to synthesize tissue proteins for the repair and growth of muscle tissue damaged after exercise, and some are used to synthesize various functional proteins and nitrogen containing compounds other than proteins, such as purine and creatine.After some amino acids are absorbed, they are decomposed in the body for energy supply.
When the body does not consume protein at all, the protein in the body is still decomposing and synthesizing. A 60 kg adult man still excretes 3.2 grams of nitrogen every day from urine, feces, skin and secretions, which is equivalent to 20 grams of protein.The inevitable consumption of nitrogen by the body is called "necessary nitrogen loss" when no protein is taken in at all.This means that an adult man with a weight of 60 kg should consume at least 20 grams of high-quality protein every day.Can maintain normal protein metabolism in the body.
In a certain period of time, the relationship between the amount of nitrogen ingested and the amount of nitrogen discharged is called "nitrogen balance" to measure the demand for human protein and evaluate the status of human muscle protein.
Nitrogen balance
1. Nitrogen balance: within a certain period of time, the amount of nitrogen ingested is equal to the amount of nitrogen discharged, which means that the synthesis and decomposition of protein in the human body are in balance, and the muscle circumference of the human body is in the original circumference and level.
2. Positive nitrogen balance: the amount of nitrogen intake is greater than the amount of nitrogen output, the amount of protein synthesis is greater than the amount of decomposition, and the muscle fibers damaged after exercise will quickly repair and grow.
3. Negative nitrogen balance: the amount of nitrogen ingested is less than the amount of nitrogen eliminated, and the synthesis of protein is less than the decomposition. At this time, the muscle protein of the human body is in a state of reduction to ensure the decomposition and energy supply of body activities.
matters needing attention
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Safety protection:Nitrogen is non-toxic in the form of simple substance (nitrogen), and is often toxic in the form of compound, such as ammonia, nitrite, etc.
No special protection is required when contacting nitrogen, and attention shall be paid to prevent frostbite when contacting liquid nitrogen.
