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?

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insert step 1: Understand that the oxidation number is a concept used to keep track of electrons in chemical reactions, particularly redox reactions.

insert step 2: Recognize that hydrogen typically has an oxidation number of +1 when bonded to nonmetals and -1 when bonded to metals.

insert step 3: Identify that in Group 2A metal hydrides (e.g., BeH2, MgH2), hydrogen is bonded to metals.

insert step 4: Conclude that since hydrogen is bonded to metals in these compounds, it will have an oxidation number of -1.

insert step 5: Verify that the sum of oxidation numbers in a neutral compound is zero, which supports hydrogen having an oxidation number of -1 in these metal hydrides.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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.

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?