Consider the lattice energies of the following Group 2A compounds: BeH2, 3205 kJ/mol; MgH2, 2791 kJ/mol; CaH2, 2410 kJ/mol; SrH2, 2250 kJ/mol; BaH2, 2121 kJ/mol. (a) What is the oxidation number of H in these compounds?

Key Concepts

Oxidation Number

The oxidation number, or oxidation state, is a theoretical charge assigned to an atom in a compound based on the assumption that electrons are completely transferred. In compounds, hydrogen typically has an oxidation number of +1 when bonded to nonmetals and -1 when bonded to metals. Understanding this concept is crucial for determining the oxidation states of elements in various compounds.

Group 2A Elements

Group 2A elements, also known as alkaline earth metals, include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). These elements typically have an oxidation state of +2 in their compounds due to the loss of their two outermost electrons. Recognizing the behavior of these metals helps in predicting the oxidation states of hydrogen in their hydrides.

Hydrides

Hydrides are compounds formed between hydrogen and other elements, where hydrogen can exhibit different oxidation states. In the case of alkaline earth metal hydrides, hydrogen is usually in the -1 oxidation state when bonded to metals. This understanding is essential for analyzing the oxidation states in the given Group 2A hydrides.