Question

Write an equation representing each of the following: (a) the change of a magnesium atom to a magnesium ion (b) the change of a bromine atom to a bromide ion

Short answer

Equation (a) Mg → Mg²⁺ + 2e⁻, Equation (b) Br + e⁻ → Br⁻.

Step-by-step solution

Writing an Equation for the Change of a Magnesium Atom to a Magnesium Ion

Magnesium (Mg) loses two electrons to form a magnesium ion (Mg²⁺). The equation representing this change is Mg → Mg²⁺ + 2e⁻. This shows that a neutral magnesium atom becomes a positively charged magnesium ion by losing two electrons.

Writing an Equation for the Change of a Bromine Atom to a Bromide Ion

A bromine (Br) atom gains one electron to become a bromide ion (Br⁻). The equation representing this change is Br + e⁻ → Br⁻. This indicates that a neutral bromine atom becomes a negatively charged bromide ion by gaining one electron.

Key concepts

Chemical Equations

Chemical equations are the symbolic representation of chemical reactions, showing both the reactants and products with their specific quantities. In teaching students about chemical equations, it's essential to emphasize the Law of Conservation of Mass. This law states that in a chemical reaction, matter is neither created nor destroyed; hence, the number of atoms for each element remains the same before and after the reaction.

For example, when writing the ionization equation for magnesium, as shown in the exercise, \( Mg \rightarrow Mg^{2+} + 2e^- \), it's necessary to show the one magnesium atom on the reactant side and then account for the loss of two electrons to form one \( Mg^{2+} \) ion. This equation demonstrates the conversion of a magnesium atom to a positively charged ion by the emission of electrons and adheres to the conservation of mass. To aid student comprehension, encourage the practice of balancing chemical equations and looking closely at how atoms transition between different ionic and elemental states.

Oxidation States

Oxidation states are a way of keeping track of electrons in chemical reactions, particularly redox reactions where oxidation and reduction occur. The oxidation state is a hypothetical charge that an atom would have if all bonds to atoms of different elements were completely ionic. Grasping this concept is crucial as it determines which atom is oxidized and which is reduced during a reaction.

In the provided exercise, magnesium starts with an oxidation state of 0 (as it is an element) and ends with an oxidation state of +2 in the magnesium ion \(Mg^{2+}\). On the other hand, a bromine atom, which also begins with an oxidation state of 0, ends with an oxidation state of -1 when it becomes the bromide ion \(Br^-\). In a classroom setting, visual aids, such as oxidation state tables and examples with common elements, can significantly improve students' understanding of how atoms either lose or gain electrons to change their oxidation states.

Electron Transfer Reactions

Electron transfer reactions, commonly known as redox reactions, are chemical processes involving the movement of electrons between two species. These reactions can further be broken down into two half-reactions: oxidation, where an atom loses electrons, and reduction, where an atom gains electrons. Oxidation numbers change as a result of electron transfers, serving as an indicator of whether a species is being oxidized or reduced.

For instance, in the electron transfer that forms a magnesium ion, \( Mg \rightarrow Mg^{2+} + 2e^- \), magnesium undergoes oxidation by losing two electrons. Conversely, bromine undergoes reduction when it gains an electron, \( Br + e^- \rightarrow Br^- \). Teaching students to identify what is being oxidized and what is being reduced in an electron transfer reaction can reinforce their overall understanding of redox processes. Interactive activities such as predicting outcomes of simple redox reactions and correlating them with their everyday applications can engage students and make the concept more relatable.