Covalent compounds, and

Both boron and aluminium chlorides can be prepared by the direct combination of the elements. Boron trichloride can also be prepared by passing chlorine gas over a strongly heated mixture of boron trioxide and carbon. Like boron trifluoride, this is a covalent compound and a gas at ordinary temperature and pressure (boiling point 285 K). It reacts vigorously with water, the mechanism probably involving initial co-ordination of a water molecule (p, 152). and hydrochloric acid is obtained ... 

The degree of polarity has considerable influence on the physical properties of covalent compounds and it can also affect chemical reactivity. The melting point (mp) and boiling point (bp) are higher in ionic substances due to the strong nature of the interionic forces, whereas the covalent compounds have lower values due to the weak nature of intermolecular forces. 

Beryllium compounds are very toxic and must be handled with great caution. Their properties are dominated by the highly polarizing character of the Be2+ ion and its small size. The strong polarizing power results in moderately covalent compounds, and its small size limits to four the number of groups that can attach to the ion. These two features together are responsible for the prominence of the... 

In each case the mechanism involves generation of an aryl radical from a covalent azo compound. In acid solution diazonium salts are ionic and their reactions are polar. When they cleave, the product is an aryl cation (see p. 852). However, in neutral or basic solution, diazonium ions are converted to covalent compounds, and these cleave to give free radicals ... 

Oxidation-Reduction Reactions between Covalent Compounds and Metal Ions... 

The periodic table can give us many clues as to the type of reaction that is taking place. One general rule, covered in more detail in the Bonding chapter, is that nonmetals react with other nonmetals to form covalent compounds, and that metals react with nonmetals to... 

Consider the differences in properties between covalent compounds and ionic compounds. Do these differences imply that covalent bonds are weaker than ionic bonds Give evidence to justify your answer. 

In this section, you have used Lewis structures to represent bonding in ionic and covalent compounds, and have applied the quantum mechanical theory of the atom to enhance your understanding of bonding. All chemical bonds—whether their predominant character is ionic, covalent, or between the two—result from the atomic structure and properties of the bonding atoms. In the next section, you will learn how the positions of atoms in a compound, and the arrangement of the bonding and lone pairs of electrons, produce molecules with characteristic shapes. These shapes, and the forces that arise from them, are intimately linked to the physical properties of substances, as you will see in the final section of the chapter. 

Greater ratios up to H M = 4.5, for example in BaReHg, have been found [43] however, all hydrides with a hydrogen to metal ratio of more than 2 are ionic or covalent compounds and belong to the complex hydrides. 

Analytical Procedures and Tests for Guanidine and Its Salts. Gu, urea, their salts, covalent compounds, and polymers have the properry of evolving ammonia when heated to 250°, which is not shared by other amines or amides. Thus, after a preliminary heating at 1800 for several... 

Naming Molecular (CoValent) Compounds and Writing Their Formulas... 

From the foregoing you may anticipate that the chemistry of carbon compounds will be largely the chemistry of covalent compounds and will not at all resemble the chemistry of inorganic salts such as sodium chloride. You also may anticipate that the major differences in chemical and physical properties of organic compounds will arise from the nature of the other elements bonded to carbon. Thus methane is not expected to, nor does it have, the same chemistry as other one-carbon compounds such as methyllithium, CH3Li, or methyl fluoride, CH3F. 

This exercise will familiarise you with (he structures of some simple covalent compounds and the methods we have for representing the structure and shape of their molecules. 

Finally, it was a great surprise to discover that tellurium, a typical semimetal, undergoes reactions typical of covalent compounds and that none of the Te-N bonds containing heterocyclic molecules so far prepared tend to explode. 

Name three characteristics of covalent compounds and three characteristics of ionic compounds. 

---