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Nitrogen oxides mainly include nitrous oxide (N 2 O), nitric oxide (NO), nitrous oxide (N 2 O 3 ), and nitrogen dioxide (NO 2 , whose dimer is N 2 O 4 ) And dinitrogen pentoxide (N 2 O 5 ), most of these nitrogen oxides have delocalized π bonds (Figure 12-6)
.
N 2 O 5 is solid at room temperature , and other nitrogen oxides are gases
Figure 12-6 The structure and π bond of nitrogen oxide
1.
Nitrous oxide
N 2 O is a colorless gas at room temperature (boiling point -88.
46°C)
.
N 2 O is a polar molecule, but its solubility in water is small (1 volume of water can dissolve 0.
Carefully heat at about 250°C to decompose ammonium nitrate to obtain N2O
.
NH 4 NO 3 =N 2 O↑+2H 2 O
The N 2 O molecule has a linear structure, and N 3 - is an isoelectronic body
.
Is generally considered within the molecule 2 delocalized Ⅱ .
Figure 12-7 Structure and π bond of NO molecule
2.
Nitric oxide
NO is a colorless gas (boiling point -151.
8°C)
.
NO molecules on the N atom has a lone pair of electrons, has a coordination ability, and as of Fe 2+ to generate [Fe (NO)] 2+ or [of Fe (NO) (H 2 O) .
NO disproportionates under high pressure and heating:
Industrially, NO is produced by catalytic oxidation of ammonia, and NO is produced by reacting dilute nitric acid with inert metals in the laboratory
.
3Cu+8HNO 3 =3Cu(NO 3 ) 2 +2NO↑+4H 2 O
3.
Dinitrogen trioxide
N 2 O 3 is a planar molecule, which can be regarded as a bond between NO 2 and NO through two N atoms
.
Since the NN bond length (186pm) is longer than the single bond (145pm), it indicates that the five-center delocalized π bond is not formed in the molecule
At low temperature, NO interacts with NO 2 to generate N 2 O 3
.
NO+NO 2 =N 2 O 3
N 2 O 3 has a melting point of -100.
7°C and a boiling point of about 3.
5°C
.
Solid N 2 O 3 is blue, and liquid is light blue
N 2 O 3 =NO+NO 2
4.
Nitrogen dioxide and dinitrogen tetroxide
NO is quickly oxidized by O 2 in the air to produce NO 2 , and some gases from thermal decomposition of nitrate contain NO 2
.
NO 2 is a reddish-brown gas, within the molecule delocalized Ⅱ .
4 .
3 key, ∠ONO = 134 [deg.
]
.
NO 2 easily polymerizable, bond angle is large (much greater than 120 °), indicates that the molecule has a single electron, is also supported within the molecule Ⅱ .
4 .
3 key instead Ⅱ .
3 .
3 view bond
.
NO 2 has strong oxidizing properties
.
NO 2 disproportionates with water to form HNO 3 and NO, and disproportionates to form NO 3 - and NO 2 - in alkali
.
After NO 2 polymerization, a colorless N 2 O 4 gas is obtained, and NO 2 and N 2 O 4 quickly reach equilibrium
.
In the N 2 O .
4 NN bond length of 175pm (longer than a single bond) in the molecule, indicating that the molecule can not form a delocalized π bond six centers, but the formation of three-center two delocalized Ⅱ .
4 .
3 bonds
.
The melting point of N 2 O 4 is -9.
3°C and the boiling point is 21.
15°C
.
At temperatures below the melting point, all of the solid is N 2 O 4
.
At the boiling point temperature, the liquid contains 1% NO 2 and the gas contains 15.
9% NO 2 ; when the temperature rises to 135°C, the proportion of NO 2 accounts for 99%
.
5.
Dinitrogen Pentoxide
N 2 O 5 is a strong oxidant, which is solid at room temperature (melting point 30°C, boiling point 47°C), and sublimates at 32.
4°C under normal pressure
.
N 2 O 5 is the acid anhydride of nitric acid.
N 2 O 5 can be obtained by dehydrating HNO 3 or oxidizing NO 2 with a strong oxidant .
Gaseous N 2 O .
5 within the molecule 2 delocalized Ⅱ .
4 .
3 bonds
.
The solid N 2 O 5 is an ionic crystal with a composition of [NO 2 ] + [NO 3 ] -
.
When the temperature is higher than room temperature, both solid and gaseous are unstable and decompose into NO 2 and O 2
.
