Question

Provide the formula for each of the following binary ionic compounds: (a) cuprous sulfide (b) ferrous phosphide (c) mercuric iodide (d) plumbic oxide

Short answer

Cu₂S, Fe₃P₂, HgI₂, PbO₂.

Step-by-step solution

Identify Ion Charges

Understanding the charges of the ions is critical for forming the compounds. Cuprous ion is copper(I) with a charge of +1, ferrous ion is iron(II) with a charge of +2, mercuric ion is mercury(II) with a charge of +2, and plumbic ion is lead(IV) with a charge of +4.

Identify Anion Charges

The sulfide ion, phosphide ion, iodide ion, and oxide ion come from sulfur, phosphorus, iodine, and oxygen, respectively. These ions have the charges of -2, -3, -1, and -2.

Write the Formula for Cuprous Sulfide

To balance the charges for cuprous sulfide, we combine two copper ions (each +1) with one sulfide ion (-2) to get the neutral compound Cu₂S.

Write the Formula for Ferrous Phosphide

For ferrous phosphide, we need three ferrous ions (+2 each) to balance with two phosphide ions (-3 each), resulting in the compound Fe₃P₂.

Write the Formula for Mercuric Iodide

Mercuric iodide combines one mercury ion (+2) with two iodide ions (-1 each), forming the compound HgI₂.

Write the Formula for Plumbic Oxide

For plumbic oxide, combine one plumbic ion (+4) with two oxide ions (-2 each) to obtain the neutral compound PbO₂.

Key concepts

Binary Ionic Compounds

Binary ionic compounds are made from two different elements. These components include a metal and a nonmetal, which chemically combine through ionic bonds. These compounds form when atoms transfer electrons, allowing the metal to lose electrons and become a positively charged ion. Meanwhile, the nonmetal gains those electrons, becoming a negatively charged ion. For example, in the case of cuprous sulfide (Cu₂S), copper, a metal, lends electrons to sulfur, a nonmetal. Together they form a stable ionic compound. Understanding binary ionic compounds is crucial because they represent many naturally occurring and industrially significant substances. To write the formulas for these compounds, one must first understand the charges associated with each time, which plays a pivotal role in ensuring that the overall compound remains electrically neutral.

Ion Charges

Ion charges are crucial for forming binary ionic compounds. In essence, ions are atoms or molecules that bear an electric charge due to the loss or gain of electrons. Metals typically become cations, meaning they lose electrons and take on a positive charge. Conversely, nonmetals generally become anions, gaining electrons and acquiring a negative charge. For instance, copper in its cuprous state (Cu⁺) is a cation with a +1 charge, while sulfide (S²⁻) is an anion with a -2 charge. This means two copper ions are needed to balance each sulfide ion in cuprous sulfide (Cu₂S). It's a symbiotic relationship where charges must complement each other perfectly, ensuring the resulting compound is neutrally charged. Understanding ion charges allows one to predict how substances will interact chemically, making it a fundamental concept in chemistry.

Balancing Charges

A critical step in writing chemical formulas for binary ionic compounds is balancing charges. This means ensuring the total positive charge from the cations equals the total negative charge from the anions in a compound.

1. First, identify the charge on the metal cation and the nonmetal anion. For example, in ferrous phosphide (Fe₃P₂), iron has a +2 charge, and phosphide has a -3 charge.
2. Then, determine the smallest ratio of ions that will balance the overall charge. In Fe₃P₂, three iron ions (+6 total from three +2 ions) pair with two phosphide ions (-6 total from two -3 ions).

This technique of balancing charges ensures a correct and neutrally charged compound, which is key for correctly formulating chemical equations. Balancing charges strengthens our ability to predict the composition of unfamiliar compounds, enhancing our understanding of chemistry.