Question

Complete the table by filling in the formula for the ionic compound formed by each pair of cations and anions, as shown for the first pair. $$\begin{array}{|lcccc|}\hline \text{ Ion }& {\mathrm{Na}}^{+}& {\mathrm{Ca}}^{2+}& {\mathrm{Fe}}^{2+}& {\mathrm{Al}}^{3+}\\ {\mathrm{O}}^{2-}& {\mathrm{Na}}_2\mathrm{O}& & & \\ {\mathrm{NO}}_3^{-}& & & & \\ {\mathrm{SO}}_4{}^{2-}& & & & \\ {\mathrm{AsO}}_4{}^{3-}& & & & \\ \hline\end{array}$$

Short answer

The completed table of ionic compounds is as follows: $$\begin{array}{|lcccc|}\hline \text{ Ion }& {\mathrm{Na}}^{+}& {\mathrm{Ca}}^{2+}& {\mathrm{Fe}}^{2+}& {\mathrm{Al}}^{3+}\\ {\mathrm{O}}^{2-}& {\mathrm{Na}}_2\mathrm{O}& \mathrm{CaO}& \mathrm{FeO}& {\mathrm{Al}}_2{\mathrm{O}}_3\\ {\mathrm{NO}}_3^{-}& {\mathrm{NaNO}}_3& {\mathrm{Ca}(\mathrm{NO}}_3{)}_2& {\mathrm{Fe}(\mathrm{NO}}_3{)}_2& {\mathrm{Al}(\mathrm{NO}}_3{)}_3\\ {\mathrm{SO}}_4{}^{2-}& {\mathrm{Na}}_2{\mathrm{SO}}_4& {\mathrm{CaSO}}_4& {\mathrm{FeSO}}_4& {\mathrm{Al}}_2{(\mathrm{SO}}_4{)}_3\\ {\mathrm{AsO}}_4{}^{3-}& {\mathrm{Na}}_3{\mathrm{AsO}}_4& {\mathrm{Ca}}_3{(\mathrm{AsO}}_4{)}_2& {\mathrm{Fe}}_3{(\mathrm{AsO}}_4{)}_2& {\mathrm{AlAsO}}_4\\ \hline\end{array}$$

Step-by-step solution

Understanding Ionic Compound Formation

Ionic compounds form when a metal (cation) transfers one or more electrons to a non-metal (anion), resulting in a neutral compound. The charges between cations and anions must balance each other, meaning the overall charge of the ionic compound must be zero. With this in mind, we can complete the given table by finding the appropriate ratio of ions to achieve a neutral compound and writing its chemical formula.

Complete the table for Calcium (Ca^2+)

1. Pair Ca^2+ with O^2-: They both have a charge of 2, but with opposite signs, so they will combine in a 1:1 ratio to form CaO. 2. Pair Ca^2+ with NO_3^-: Ca has a +2 charge, while NO_3^- has a -1 charge. The compound needs two NO_3^- ions to balance the +2 charge of Ca. The formula is Ca(NO_3)_2. 3. Pair Ca^2+ with SO_4^2-: They both have a charge of 2, but with opposite signs, so they will combine in a 1:1 ratio to form CaSO_4. 4. Pair Ca^2+ with AsO_4^3-: Ca has a +2 charge, while AsO_4 has a -3 charge. The ion charges can be balanced by combining three Ca^2+ ions with two AsO_4^3- ions, resulting in a formula of Ca_3(AsO_4)_2.

Complete the table for Iron (Fe^2+)

1. Pair Fe^2+ with O^2-: They both have a charge of 2, but with opposite signs, so they will combine in a 1:1 ratio to form FeO. 2. Pair Fe^2+ with NO_3^-: Fe has a +2 charge, while NO_3^- has a -1 charge. The compound needs two NO_3^- ions to balance the +2 charge of Fe. The formula is Fe(NO_3)_2. 3. Pair Fe^2+ with SO_4^2-: They both have a charge of 2, but with opposite signs, so they will combine in a 1:1 ratio to form FeSO_4. 4. Pair Fe^2+ with AsO_4^3-: Fe has a +2 charge, while AsO_4 has a -3 charge. The ion charges can be balanced by combining three Fe^2+ ions with two AsO_4^3- ions, resulting in a formula of Fe_3(AsO_4)_2.

Complete the table for Aluminum (Al^3+)

1. Pair Al^3+ with O^2-: Al has a +3 charge, while O has a -2 charge. The ion charges can be balanced by combining two Al^3+ ions with three O^2- ions, resulting in a formula of Al_2O_3. 2. Pair Al^3+ with NO_3^-: Al has a +3 charge, while NO_3^- has a -1 charge. The compound needs three NO_3^- ions to balance the +3 charge of Al. The formula is Al(NO_3)_3. 3. Pair Al^3+ with SO_4^2-: Al has a +3 charge, while SO_4^2- has a -2 charge. The ion charges can be balanced by combining two Al^3+ ions with three SO_4^2- ions, resulting in a formula of Al_2(SO_4)_3. 4. Pair Al^3+ with AsO_4^3-: They both have a charge of 3, but with opposite signs, so they will combine in a 1:1 ratio to form AlAsO_4. Now the table is complete: $$\begin{array}{|lcccc|}\hline \text{ Ion }& {\mathrm{Na}}^{+}& {\mathrm{Ca}}^{2+}& {\mathrm{Fe}}^{2+}& {\mathrm{Al}}^{3+}\\ {\mathrm{O}}^{2-}& {\mathrm{Na}}_2\mathrm{O}& \mathrm{CaO}& \mathrm{FeO}& {\mathrm{Al}}_2{\mathrm{O}}_3\\ {\mathrm{NO}}_3^{-}& {\mathrm{NaNO}}_3& {\mathrm{Ca}(\mathrm{NO}}_3{)}_2& {\mathrm{Fe}(\mathrm{NO}}_3{)}_2& {\mathrm{Al}(\mathrm{NO}}_3{)}_3\\ {\mathrm{SO}}_4{}^{2-}& {\mathrm{Na}}_2{\mathrm{SO}}_4& {\mathrm{CaSO}}_4& {\mathrm{FeSO}}_4& {\mathrm{Al}}_2{(\mathrm{SO}}_4{)}_3\\ {\mathrm{AsO}}_4{}^{3-}& {\mathrm{Na}}_3{\mathrm{AsO}}_4& {\mathrm{Ca}}_3{(\mathrm{AsO}}_4{)}_2& {\mathrm{Fe}}_3{(\mathrm{AsO}}_4{)}_2& {\mathrm{AlAsO}}_4\\ \hline\end{array}$$

Key concepts

Cation-Anion Pairing

Pairing cations and anions to form ionic compounds is like finding the perfect combination to ensure charges are balanced. Cations are positively charged ions, usually metals, while anions are negatively charged ions, typically non-metals or polyatomic ions. When forming an ionic compound, each cation pairs with one or more anions in a way that the positive and negative charges cancel each other out.

For example, calcium (Ca) with a charge of +2 will pair with nitrate (NO₃), which has a -1 charge. To balance the charges, two nitrate ions are needed for every calcium ion, leading to the compound Ca(NO₃)₂.

• Ca⁺² pairs with O⁻² to form CaO
• Ca⁺² pairs with NO₃⁻ to form Ca(NO₃)₂
• Ca⁺² pairs with SO₄⁻² to form CaSO₄

The goal is always to have the total positive and negative charges in the compound equal to ensure neutrality.

Charge Balance

Charge balance is crucial in writing the correct formula for an ionic compound. The total positive charge from cations and the total negative charge from anions must be equal. This principle ensures the compound is electrically neutral.

For instance, aluminum (Al) has a +3 charge, and oxygen (O) has a -2 charge. To balance this, two aluminum ions must pair with three oxygen ions, resulting in Al₂O₃. Here are some methods to achieve charge balance:

• Determine the charge of each ion. For example, Fe⁺² and SO₄⁻².
• Calculate the lowest common multiple of the charges to determine the ratio.
• Use subscripts to represent the correct ratio of ions in the compound.

Balanced ionic formulas ensure compounds are stable and neutral.

Chemical Formula Writing

Writing chemical formulas for ionic compounds involves combining the ratios of cations and anions determined from charge balancing. Once the charges are balanced, the compound's formula can be written using subscripts to show how many of each ion are present.

Start with the cation and place the number of bonded anions as a subscript if needed. For example, for sodium oxide, you have Na⁺ and O⁻². Sodium has a +1 charge, so two sodium ions are needed to balance one oxygen ion, resulting in Na₂O.

• Sodium nitrate: NaNO₃; simple 1:1 ratio.
• Iron sulfate: FeSO₄; already balanced automatically.
• Iron arsenate: Fe₃(AsO₄)₂; ratio derived from electrical neutrality.

These rules ensure clarity in chemical formulas, making it easy to understand the compound's composition.