Hydrides of Nonmetals. Hydrocarbons

The element iodine (from Greek iodes, violet) occurs as iodide ion, 1, in very small quantities in seawater, and, as sodium iodate, NalOa, in deposits of Chile saltpeter. It is made commercially from sodium iodate obtained from saltpeter, from kelp, which concentrates it from the seawater, and from oil-well brines. 

The elements carbon, nitrogen, oxygen, and fluorine and their congeners form simple hydrides with composition corresponding to their normal covalences (CH4, NH3, HgO, HF). Some properties of these hydrides are given in Table 7-4. 

The tetrahydrides (CH4 to SnH4) have a regular tetrahedral structure, corresponding to the use of sp tetrahedral bond orbitals by the central atom (bond angles 109.5°, Section 6-5). The other hydrides have smaller bond angles, approaching 90°, the value for/ bond orbitals (Section 6-7). 

Formula Melting Point Boiling Point Density of Liquid Standard Enthalpy (g) Bond Length Bond Angle 

Standard heat of formation per bond of hydrides (g) of nonmetallic elements, compared with values calculated by the electronegativity equation. 

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Nonmetals form covalent molecular hydrides, which consist of discrete molecules. These compounds are volatile and many are Bronstcd acids. Some are gases— for example, ammonia, the hydrogen halides (HF, HC1, HBr, HI), and the lighter hydrocarbons such as methane, ethane, ethene, and ethyne. Liquid molecular hydrides include water and hydrocarbons such as octane and benzene. 

H2, hydrogen, is a colorless, odorless, tasteless, nonpolar, diamagnetic, diatomic gas with the lowest atomic weight and density of any known substance. It has low solubility in water and is very flammable. Hydrogen is prepared by reactions of metals with water, steam or various acids, electrolysis of water, the water gas reaction and thermal cracking of hydrocarbons. It combines with metals and nonmetals to form hydrides. 

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