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Exercise 8.

a)Describe any alkali element on the following plan:

1. boiling point;

2. melting point;

3. atomic number;

4. relative density;

5. valence;

6. Is it a metal or non-metal ?;

7. What group does it belong to?;

8. colour;

9. odour;

10. Where is it used?;

11. What substances does it react with?;

12. What chemical compounds does it have?.

b)Choose any two alkali elements and compare them on the following plan using comparative and superlative degree:

1. melting point;

2. boiling point;

3. relative density;

4. atomic and ionic radius;

5. relative atomic mass

Texts for educational purposes

Clay and its minerals

Clay is a fine-grained deposit consisting chiefly of clay minerals. It is characteristically plastic and virtually impermeable when wet and cracks when it dries out. In geology the size of the constituent particles is usually taken to be less than 1/256 mm. In soil science clay is regarded as a soil with particles less than 0.002 mm in size.

Clay minerals are very small particles, chiefly hydrous silicates of aluminium, sometimes with magnesium and/or iron substituting for all or part of the aluminium, that are the major constituents of clay materials. The particles are essentially crystalline (either platy or fibrous) with a layered structure, but may be amorphous or metalloidal. The clay minerals are responsible for the plastic properties of clay; the particles have the property of being able to hold water. The chief groups of clay minerals are: Al₄Si₄O₁₀(OH)₈, the chief constituent of kaolin; halloysite, kaolinite, Al₄Si₄(OH)₈O_I0.4H₂O; illite, KAl₄(SiAl)₈ O₁₈.2H₂O; montmorillonite, (Na,Ca)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂.nH₂O, formed chiefly through alteration of volcanic ash; and vermiculite, (Mg,Fe,Al)₃(Al,Si)₄O₁₀(OH)₂.4H₂O, used as an insulating material and potting soil.

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