Question

Provide the formula for each of the following binary ionic compounds: (a) copper(I) oxide (b) iron(III) nitride (c) mercury(II) chloride (d) lead(IV) sulfide

Short answer

(a) Cu₂O, (b) FeN, (c) HgCl₂, (d) PbS₂.

Step-by-step solution

Identify the Cation and Anion

For each compound, we need to determine the cation (positive ion) and the anion (negative ion) from the chemical name. In binary ionic compounds, the cation is usually a metal or a positive ion, while the anion is a non-metal or a negative ion: (a) Copper(I) oxide contains Cu⁺ (copper ion with a +1 charge) as the cation and O²⁻ (oxide ion) as the anion. (b) Iron(III) nitride contains Fe³⁺ (iron ion with a +3 charge) as the cation and N³⁻ (nitride ion) as the anion. (c) Mercury(II) chloride contains Hg²⁺ (mercury ion with a +2 charge) as the cation and Cl⁻ (chloride ion) as the anion. (d) Lead(IV) sulfide contains Pb⁴⁺ (lead ion with a +4 charge) as the cation and S²⁻ (sulfide ion) as the anion.

Balance Charges for Compound Formation

To form a neutral binary ionic compound, the total positive charge must equal the total negative charge.(a) For copper(I) oxide, Cu⁺ and O²⁻ will combine as two Cu⁺ ions for each O²⁻ to balance the charges: - \[ \text{Cu}_2\text{O} \](b) For iron(III) nitride, the charges of Fe³⁺ and N³⁻ balance in a 1:1 ratio: - \[ \text{FeN} \](c) For mercury(II) chloride, one Hg²⁺ balances with two Cl⁻ ions: - \[ \text{HgCl}_2 \](d) For lead(IV) sulfide, one Pb⁴⁺ balances with two S²⁻ ions: - \[ \text{PbS}_2 \]

Write the Formula

Using the balanced formulas from Step 2, write the correct chemical formula for each ionic compound.(a) Copper(I) oxide: - \[ \text{Cu}_2\text{O} \](b) Iron(III) nitride: - \[ \text{FeN} \](c) Mercury(II) chloride: - \[ \text{HgCl}_2 \](d) Lead(IV) sulfide: - \[ \text{PbS}_2 \]

Key concepts

Ionic Compound Formulas

When writing formulas for binary ionic compounds, it's vital to understand that these compounds are made up of two different elements: a metal and a non-metal. The metal, or cation, is usually listed first and is positively charged, while the non-metal, or anion, is negatively charged. This order is due to the nature of ionic bonds, which are said to be formed from an attraction between oppositely charged ions.

In a binary ionic formula, the charges of the ions must balance, resulting in a neutral compound. The subscript numbers in the chemical formula represent the smallest ratio of cations to anions required to balance these charges.

For example, in copper(I) oxide, the formula is written as \( \text{Cu}_2\text{O} \). This indicates that there are two copper ions for each oxide ion. Understanding the process of balancing these charges is essential for correctly writing the formulas of ionic compounds.

Cation and Anion Identification

Identifying cations and anions in ionic compounds is crucial because it determines how you'll balance the charges later. Cations are often metals that lose electrons, giving them a positive charge. Conversely, anions are non-metals that gain electrons, so they have a negative charge.

To identify these ions from a compound's name:

• Cations are generally named first and often involve metals. For instance, in iron(III) nitride, 'iron(III)' suggests the cation is iron with a +3 charge (Fe³⁺).
• Anions typically follow and are often designated by either the name of the non-metal ending in '-ide,' such as 'nitride,' which is N³⁻ in iron(III) nitride.

Correctly identifying these ions sets the stage for accurately balancing charges and writing formulas. This understanding will also aid in predicting how different elements combine to form a variety of compounds.

Balancing Charges

Balancing charges is the step that ensures your ionic compound is neutral overall, which is how compounds naturally occur. The total charge from the cations must equal the total charge from the anions. This balance is achieved by adjusting the subscripts in the formula.

Consider mercury(II) chloride: mercury(II) means Hg²⁺. Chloride is Cl⁻. Since two chloride ions each contribute a -1 charge (-2 in total), they balance the +2 charge from one mercury ion.

The resulting balanced formula is \( \text{HgCl}_2 \). This method of charge balancing ensures that each compound you write down adheres to the basic rule of neutrality found in nature. It's like solving a simple math equation where the positive and negative parts must cancel each other out.