Select one of the alkaline earth metals and write a balanced chemical equation for its reaction with oxygen. Is the reaction likely to be exothermic or endothermic? Is the product ionic or molecular?

Interpretation: To write a balanced chemical equation of an alkaline earth metal with oxygen.

Concept introduction: Alkaline earth metals belongs to group 2A of the periodic table. It consists of elements beryllium, magnesium, calcium, strontium, barium, and radium. All of them have two electrons in their outermost shell. They are all metals and tend to lose their valence electrons. Thus, they have +2 oxidation number.

Alkaline earth metals are very reactive and form compounds with chlorides, oxides and water. Alkaline earth metals combine with non-metals and there is a transfer of electrons from metals to non-metals and thus ions are formed where metals have a positive charge and non-metals are negatively charged. Thus, alkaline earth metals generally form ionic compounds and react vigorously to produce compounds with non-metals.

The reaction of alkaline earth metals with non-metals produces energy which is released in the form of heat or light. Such reactions, in which energy is released in the form of heat and light are referred to as exothermic reactions. The reaction in which energy is absorbed from the surroundings are known as endothermic reactions.

In general, combination reaction are always exothermic in nature. Thus, exothermic reaction gives off energy and endothermic reactions absorb energy.

In order to have a balanced chemical equation, the atoms on both the product and reactant side of a combination reaction should be same. Thus, the stoichiometric coefficients are multiplied with the compounds in the chemical equation to have an equal number of atoms on both sides of the equation.

The alkaline earth metal selected is Calcium.

The electronic configuration of calcium is [Ar]4s2. It has two valence electron in its outermost shell. It loses this electron to form monoatomic ion Ca2+ which has noble gas configuration.

The electronic configuration of oxygen is [He]2s22p4. It has six valence electron in its outermost shell. Oxygen gains two electrons to form monoatomic ion O2− which has noble gas configuration.

Thus, the oxidation number of calcium ion is +2 and oxygen ion is −2. Hence, the compound formed on combination of calcium with oxygen is CaO