TRENDS FOR SELECTED NONMETALS

We have seen that the chemistry of the alkali metals is dominated by the loss of their outer ns electron to form cations. The Is electron configuration of hydrogen suggests that its chemistry should have some resemblance to that of the alkali metals. The chemistry of hydrogen is much richer and more complex than that of the alkali metals, however, mainly because the ionization energy of hydrogen, 1312 kj/mol, is more than double that of any of the alkali metals. As a result, hydrogen is a nonmetal that occurs as a colorless diatomic gas, H2( ), under most conditions. 

The reactivity of hydrogen with nonmetals reflects its much greater tendency to hold on to its electron relative to the alkali metals. Unlike the alkali metals, hydrogen reacts with most nonmetals to form molecular compounds in which its electron is shared with, rather than completely transferred to, the other nonmetal. For example, we have seen that sodium metal reacts vigorously with chlorine gas to produce the ionic 

By contrast, molecular hydrogen reacts with chlorine gas to form hydrogen chloride gas, which consists of HCl molecules  

Hydrogen readily forms molecular compounds with other nomnetcds, such as the formation of water, H20(/) ammonia, NH3( ) and methane, CH4( ). The ability of hydrogen to form bonds with carbon is one of the most important cispects of organic chemistry, as will see in later chapters. 

We have seen that, particularly in the presence of water, hydrogen does readily form ions in which the hydrogen atom has lost its electron, cco (Section 4.3) For example, HC1( ) dissolves in H2O to form a solution of hydrochloric add, HCl(aq), in which the electron of the hydrogen atom is transferred to the chlorine atom—a solution of hydrochloric acid consists largely of H (aq) cuid ClT aq) ions stabilized by the H2O solvent. Indeed, the ability of molecular compoimds of hydrogen with nonmetals to form acids in water is one of the most importcuit aspects of aqueous chemistry. We will discuss the chemistry of acids and bases in detail later in the text, particularly in Chapter 16. 

Because hydrogen has the electron configuration Is, its usual position in the periodic table is above the alkali metals. However, hydrogen does not truly belong to any particular group. Unlike the alkali metals, it is a nonmetal that occurs as a colorless diatomic gas, H2(g), under most conditions. 

We saw in Equation 7.16 that hydrogen reacts with active metals to form solid metal hydrides that contain the hydride ion, H . The fact that hydrogen can gain an electron further illustrates that it is not truly an alkali metal. In fact, in terms of chemical reactivity, hydrogen has more in common with the halogens than with the alkali metals. 

In addition to its ability to form covalent bonds and metal hydrides, probably the most important characteristic of hydrogen is its ability to lose its electron to form a cation. Indeed, the aqueous chemistry of hydrogen is dominated by the H (aq) ion. - - (Section 4.1) 

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TRENDS FOR SELECTED NONMETALS Finally, we examine some of the periodic trends in the chemistry of hydrogen and the elements in groups 6A, 7A, and 8A. 

TRENDS FOR SELECTED NONMETALS (SECTION 7.8) Hydrogen is a nonmetal with properties that are distinct from any of the groups of the periodic table. It forms molecular compounds with other non-metals, such as oxygen and the halogens. 

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