Question

Write the chemical formula for the following binary compounds given their constituent ions: (a) lithium chloride, \(\mathrm{Li}^{+}\) and \(\mathrm{Cl}^{-}\) (b) silver oxide, \(\mathrm{Ag}^{+}\) and \(\mathrm{O}^{2-}\) (c) chromium(III) iodide, \(\mathrm{Cr}^{3+}\) and \(\mathrm{I}^{-}\) (d) tin(II) nitride, \(\mathrm{Sn}^{2+}\) and \(\mathrm{N}^{3-}\)

Short answer

(a) \( \mathrm{LiCl} \); (b) \( \mathrm{Ag}_2\mathrm{O} \); (c) \( \mathrm{CrI}_3 \); (d) \( \mathrm{Sn}_3\mathrm{N}_2 \).

Step-by-step solution

Write the Formula for Lithium Chloride

Lithium chloride is composed of lithium ions, \( \mathrm{Li}^+ \), and chloride ions, \( \mathrm{Cl}^- \). To write the chemical formula, balance the charges of the ions. Since both ions have a charge of \( +1 \) and \( -1 \) respectively, they combine in a 1:1 ratio to form \( \mathrm{LiCl} \).

Write the Formula for Silver Oxide

For silver oxide, the ions are silver \( \mathrm{Ag}^+ \) and oxide \( \mathrm{O}^{2-} \). To balance the charges, two silver ions will balance with one oxide ion. Therefore, the formula is \( \mathrm{Ag}_2\mathrm{O} \).

Write the Formula for Chromium(III) Iodide

Chromium(III) iodide is composed of chromium ions, \( \mathrm{Cr}^{3+} \), and iodide ions, \( \mathrm{I}^- \). To balance the charges, three iodide ions are needed to balance one chromium ion. Thus, the formula is \( \mathrm{CrI}_3 \).

Write the Formula for Tin(II) Nitride

For tin(II) nitride, the ions are \( \mathrm{Sn}^{2+} \) and \( \mathrm{N}^{3-} \). To balance the charges, two tin ions are needed for every three nitride ions, leading to the formula \( \mathrm{Sn}_3\mathrm{N}_2 \).

Key concepts

Ionic Compounds

Ionic compounds are formed through the transfer of electrons from one atom to another. This transfer usually happens between a metal and a non-metal. Metals, found on the left side of the periodic table, tend to lose electrons and form positive ions or cations. Non-metals, usually located on the right side, typically gain electrons to form negative ions called anions. The strong electrostatic forces between oppositely charged ions hold these compounds together, creating a stable ionic structure.

Some key properties of ionic compounds include:

• High melting and boiling points due to strong ionic bonds
• Conductivity in molten or dissolved states (when ions are free to move)
• Formation of crystalline solid structures

The formation of ionic compounds like the ones in the exercise involves the precise pairing of ions to ensure electrical neutrality.

Charge Balancing

Charge balancing is an essential concept in chemistry, particularly when dealing with ionic compounds. An ionic compound is electrically neutral, meaning the total positive charge of the cations must equal the total negative charge of the anions. When writing chemical formulas, the goal is to balance these charges to achieve neutrality.

To balance charges, consider the following steps:

• Identify the charges of the cation and anion involved.
• Determine the smallest ratio between ions that will result in a neutral compound.
• Use subscripts in the chemical formula to indicate the number of each ion necessary to balance the charge.

For example, in silver oxide, to neutralize two positive charges from two silver ions ( \(2 \times +1 = +2\) ), a single oxide ion with a negative charge of \(-2\) is required. This results in the formula \(\mathrm{Ag}_2\mathrm{O}\) .

Binary Compounds

Binary compounds consist of only two different elements. These compounds are named with the cation (positive ion) first followed by the anion (negative ion). They cover both ionic and covalent substances, but in the context of this exercise, we're focusing on ionic binary compounds.

Let's break down the naming process for binary ionic compounds:

• The name of the metal cation comes first and uses the element's name.
• The name of the non-metal anion comes second and is modified to end in '-ide'.

In the given exercise, examples include lithium chloride ( \(\mathrm{LiCl}\) ) where lithium is the metal cation and chlorine becomes chloride as the anion.

For chromium(III) iodide ( \(\mathrm{CrI}_3\) ), the Roman numeral indicates the charge of the chromium ion, helping balance with three iodide ions.