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Boron element
Boron simple substance, there are two types, crystal boron and amorphous boron powder
.
Crystal boron is dark gray, with high melting point, hardness close to diamond, and poor chemical activity
1.
The structure of elemental boron
The basic structural unit of crystalline boron is icosahedron, and 12 boron atoms occupy the vertices of the polyhedron to form the B12 structural unit, as shown in Figure 13-8(a)
.
As shown in Figure 13-8(b), the 6 B atoms (dark color) in the middle constitute (a)(b) into a six-membered ring, which is not planar; the six-membered ring is up and down Each has 1 three-membered ring, parallel to each other
Figure 13-8 The basic structural unit of crystalline boron
2.
Preparation of elemental boron
Under high temperature conditions, metal Mg can reduce B 2 O 3 to produce crude boron
.
BB 2 O 3 +3Mg=2B+3MgO
Under high temperature conditions, BBr 3 can be reduced with H 2 to obtain high-purity elemental boron .
2BBr 3 +3H 2 =2B+6HBr
High-temperature decomposition of BI 3 can also obtain high-purity elemental boron (a-diamond B)
.
2BI 3 =2B+3I 2
3.
The properties of elemental boron
Element B is inactive at room temperature, basically does not react with other elements, and only reacts with F 2 to generate BF 3
.
2B+3F 2 =2BF 3
Element B is more active at high temperature and can react with many elements
.
B does not react with non-oxidizing acids, but can be dissolved in hot concentrated HNO 3 or concentrated H 2 SO 4
.
In the presence of oxidant, B can be oxidized by eutectic with strong base
2B+3KNO 3 +2NaOH=2NaBO 2 +3KNO 2 +H 2 O
Related links: Germanium, tin, lead halides and sulfides
