(a) As described in Section 7.7, the alkali metals react...

(a) As described in Section 7.7, the alkali metals react with hydrogen to form hydrides and react with halogens to form halides. Compare the roles of hydrogen and halogens in these reactions. How are the forms of hydrogen and halogens in the products alike? (b) Write balanced equations for the reaction of fluorine with calcium and for the reaction of hydrogen with calcium. What are the similarities among the products of these reactions?

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Key Concepts

Electron Transfer in Redox Reactions

In these reactions, the metal(s) undergo oxidation by donating electrons, while the nonmetals (whether hydrogen or halogens) undergo reduction by accepting electrons. This electron transfer is the core of a redox reaction and is necessary for the formation of ionic compounds. The metals form cations, and the hydrogen (as hydride, H–) and halogens (as halide ions, X–) form anions.

Ionic Bonding and Compound Formation

The products of these reactions are ionic compounds formed by the electrostatic attraction between positively charged metal cations and negatively charged nonmetal anions. Whether hydrogen or a halogen is involved, the resulting compound exhibits a lattice structure typical of ionic materials, with similar overall stoichiometry and bonding characteristics.

Role of Nonmetals as Electron Acceptors

Both hydrogen (in the form of a hydride ion) and halogens (in the form of halide ions) play the analogous role of electron acceptors in these reactions. Even though their atomic compositions differ, in the context of these reactions they each gain an electron to assume a negative charge, leading to the formation of anions that pair with metal cations to produce ionic substances.

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