Question

The uranyl cation has the formula \(\mathrm{UO}_{2}^{2+}\). Propose formulas and names for the ionic compounds between the uranyl cation and \(\mathrm{F}^{-}, \mathrm{SO}_{4}^{2-}\), and \(\mathrm{PO}_{4}{ }^{3-}\).

Short answer

Uranyl compounds: \( \mathrm{UO}_2\mathrm{F}_2 \), \( \mathrm{UO}_2\mathrm{SO}_4 \), \( \left(\mathrm{UO}_2\right)_3\left(\mathrm{PO}_4\right)_2 \).

Step-by-step solution

Understanding Ionic Compound Formation

Ionic compounds are formed when cations and anions combine to neutralize their charges. In this exercise, we need to combine the uranyl cation \( \mathrm{UO}_2^{2+} \) with three different anions: \( \mathrm{F}^- \), \( \mathrm{SO}_{4}^{2-} \), and \( \mathrm{PO}_{4}^{3-} \). Each compound formed must be electrically neutral.

Combining with Fluoride

The fluoride ion \( \mathrm{F}^- \) has a single negative charge. To pair with the \( \mathrm{UO}_2^{2+} \) ion, which has a positive charge of 2, we need two fluoride ions to balance the charges. Therefore, the chemical formula for the compound is \( \mathrm{UO}_2\mathrm{F}_2 \), called uranyl fluoride.

Combining with Sulfate

The sulfate ion \( \mathrm{SO}_4^{2-} \) has the same charge magnitude as the uranyl cation \( \mathrm{UO}_2^{2+} \), which is 2. Thus, one uranyl ion pairs with one sulfate ion to balance the charges. The resulting compound is \( \mathrm{UO}_2\mathrm{SO}_4 \), named uranyl sulfate.

Combining with Phosphate

The phosphate ion \( \mathrm{PO}_{4}^{3-} \) carries a 3- charge. To combine with \( \mathrm{UO}_2^{2+} \), we need two uranyl ions to balance with three phosphate ions, making both charges combine to zero (total 6+ balanced with total 6-). The formula becomes \( \left(\mathrm{UO}_2\right)_3\left(\mathrm{PO}_4\right)_2 \), known as uranyl phosphate.

Key concepts

Uranyl Cation

The uranyl cation is a fascinating component of chemistry, primarily found in uranium compounds. Its formula is \( \mathrm{UO}_2^{2+} \), signifying that it has a positive charge of 2+. This charge comes from the uranium atom, which is part of the broader actinide series on the periodic table that possess the ability to form different oxidation states. In the uranyl cation, uranium is surrounded by two oxygen atoms in a linear arrangement, which gives it unique chemical properties.

Uranyl cations are commonly found in uranium's most stable form, making them crucial in various applications, including nuclear energy production and in some environmental studies. Since it carries this double positive charge, it readily combines with anions to form ionic compounds, bringing us to our next topic.

Chemical Formulas

Chemical formulas are a shorthand representation of the elements within a compound and their respective quantities. When constructing formulas for ionic compounds, we strive for charge neutrality, which means the total positive charges must equal the total negative charges.

In the case of the uranyl cation \( \mathrm{UO}_2^{2+} \), forming compounds with different anions involves balancing both their charges:

• With fluoride \( \mathrm{F}^- \) having a single negative charge, two fluoride ions are needed to match the 2+ charge of the uranyl ion, yielding \( \mathrm{UO}_2\mathrm{F}_2 \) (uranyl fluoride).
• Sulfate \( \mathrm{SO}_4^{2-} \) matches perfectly with one uranyl cation as both have equal and opposite charges, forming \( \mathrm{UO}_2\mathrm{SO}_4 \) (uranyl sulfate).
• Phosphate \( \mathrm{PO}_{4}^{3-} \) is a bit more complex, requiring two uranyl cations and three phosphate ions, resulting in the formula \( \left(\mathrm{UO}_2\right)_3\left(\mathrm{PO}_4\right)_2 \) (uranyl phosphate).

Mastering how to form and understand chemical formulas is essential for grasping the nature of ionic compounds.

Charge Neutralization

Charge neutralization is pivotal when forming ionic compounds, ensuring that the compound as a whole is electrically neutral. This is achieved when the total positive charge of the cations equals the total negative charge of the anions within the compound.

In the specific context of uranyl cation reactions:

• Uranyl \( \mathrm{UO}_2^{2+} \) carries a 2+ charge, demanding an equal negative charge from a combination of anions to form a balanced compound.
• For fluoride (\( \mathrm{F}^- \)), two negative charges from two fluoride ions are needed to neutralize the uranyl's positive charge.
• Sulfate \( \mathrm{SO}_4^{2-} \) perfectly balances with one uranyl ion for full neutrality because both bear a 2-charge.
• With phosphate \( \mathrm{PO}_{4}^{3-} \), achieving neutrality involves more complex balancing, as two 3- charges from phosphates require three uranyl ions, ultimately resulting in a zero net charge for chemical stability.

This understanding of charge neutralization not only forms the basis of chemical formula writing but also ensures the stability of the resultant ionic compounds.