Question

Give the formula and name for each ionic compound formed between the two listed ions. a) \(\mathrm{Mg}^{2+}\) and \(\mathrm{Cl}^{-}\) b) \(\mathrm{Fe}^{2+}\) and \(\mathrm{O}^{2-}\) c) \(\mathrm{Fe}^{3+}\) and \(\mathrm{O}^{2-}\)

Short answer

\( \mathrm{MgCl_2} \), magnesium chloride; \( \mathrm{FeO} \), iron(II) oxide; \( \mathrm{Fe_2O_3} \), iron(III) oxide.

Step-by-step solution

Identifying Ion Charges

First, identify the charges of the given ions. For part (a), we have \( \mathrm{Mg}^{2+} \) (magnesium ion) and \( \mathrm{Cl}^{-} \) (chloride ion). For part (b), the ions are \( \mathrm{Fe}^{2+} \) (iron(II) ion) and \( \mathrm{O}^{2-} \) (oxide ion). Lastly, part (c) involves \( \mathrm{Fe}^{3+} \) (iron(III) ion) and \( \mathrm{O}^{2-} \) (oxide ion).

Determining the Formula for \( \mathrm{Mg}^{2+} \) and \( \mathrm{Cl}^{-} \)

To make a neutral compound, combine \( \mathrm{Mg}^{2+} \) and \( \mathrm{Cl}^{-} \) ions such that the charges balance. Two chloride ions are needed to balance one magnesium ion, forming the compound \( \mathrm{MgCl_2} \). The name of the compound is magnesium chloride.

Determining the Formula for \( \mathrm{Fe}^{2+} \) and \( \mathrm{O}^{2-} \)

To form a neutral compound, one \( \mathrm{Fe}^{2+} \) ion combines with one \( \mathrm{O}^{2-} \) ion. Thus, the formula is \( \mathrm{FeO} \), and the compound is named iron(II) oxide.

Determining the Formula for \( \mathrm{Fe}^{3+} \) and \( \mathrm{O}^{2-} \)

Balance the charges by matching two \( \mathrm{Fe}^{3+} \) ions with three \( \mathrm{O}^{2-} \) ions to achieve neutrality. The resulting formula is \( \mathrm{Fe_2O_3} \), with the compound being named iron(III) oxide.

Key concepts

Chemical Formulas

When dealing with ionic compounds, the chemical formula tells us how many of each ion are in the compound. This is crucial for representing the balance between positive and negative charges, which ensures the compound is neutral. To write the chemical formula correctly:

• Identify the ions and their respective charges. For instance, in the example, magnesium ion has a charge of \(\mathrm{Mg}^{2+}\).
• Balance the charges using the simplest ratio of ions so that the total charge in the compound equals zero. For example, \(\mathrm{Mg}^{2+}\) and \(\mathrm{Cl}^{-}\) combine to form \(\mathrm{MgCl_2}\) because two chloride ions are needed to balance one magnesium ion.

Remember, the numbers in the chemical formula after each element, like "2" in \(\mathrm{MgCl_2}\), indicate how many of each ion are necessary. This process ensures that the resulting compound is electrically neutral.

Ion Charges

Ion charges are fundamental in forming ionic compounds. An ion is an atom or molecule that has gained or lost one or more electrons, giving it a positive or negative charge. Recognizing these charges will help you determine how to balance the ions:

• Cations are positively charged ions. For example, \(\mathrm{Mg}^{2+}\) and \(\mathrm{Fe}^{3+}\) are cations, having lost electrons.
• Anions are negatively charged ions. \(\mathrm{Cl}^{-}\) and \(\mathrm{O}^{2-}\) are anions, which have gained electrons.

To form a stable ionic compound, the charges must balance. This means the total positive charge should equal the total negative charge. For example, if you have one \(\mathrm{Fe}^{2+}\) ion and one \(\mathrm{O}^{2-}\) ion, their charges already balance, forming \(\mathrm{FeO}\). Balancing charges is essential for creating the correct ionic formula.

Compound Nomenclature

Compound nomenclature is the system used to name compounds systematically and consistently. For ionic compounds, specifically:

• Name the cation first, followed by the anion. If the cation is a metal that can form more than one type of positive ion (like iron), indicate its charge with Roman numerals in parentheses. For instance, \(\mathrm{FeO}\) is named iron(II) oxide because iron has a +2 charge, while \(\mathrm{Fe_2O_3}\) is iron(III) oxide as iron carries a +3 charge in this case.
• For the anion part, simply use its elemental name with an "-ide" ending. Thus, \(\mathrm{Cl}^{-}\) becomes "chloride," and \(\mathrm{O}^{2-}\) becomes "oxide."

This straightforward naming system helps in identifying the components and understanding the compound's structure. For instance, \(\mathrm{MgCl_2}\) is named magnesium chloride, comprising magnesium and chloride ions. Understanding compound nomenclature enables clear communication within the scientific community.