Question

Predict the chemical formula for each of the following ternary ionic compounds given the formula of scandium nitrate, \(\mathrm{Sc}\left(\mathrm{NO}_{3}\right)_{3}\) : (a) lanthanum nitrate (b) scandium nitrite

Short answer

(a) \(\mathrm{La}\left(\mathrm{NO}_{3}\right)_{3}\); (b) \(\mathrm{Sc}\left(\mathrm{NO}_{2}\right)_{3}\)."

Step-by-step solution

Understand the Composition of Scandium Nitrate

Scandium nitrate, given by the formula \(\mathrm{Sc}\left(\mathrm{NO}_{3}\right)_{3}\), is a ternary ionic compound. It consists of one scandium ion \(\mathrm{Sc}^{3+}\) and three nitrate ions \(\mathrm{NO}_{3}^{-}\). This balances the charge to make the compound neutral.

Write the Formula for Lanthanum Nitrate

Lanthanum ion is \(\mathrm{La}^{3+}\). Since nitrate is \(\mathrm{NO}_{3}^{-}\), and the charge on lanthanum must be balanced by the same number of nitrates as scandium, lanthanum nitrate has the formula \(\mathrm{La}\left(\mathrm{NO}_{3}\right)_{3}\) to maintain neutrality.

Determine the Formula for Scandium Nitrite

For scandium nitrite, replace the nitrate ion \(\mathrm{NO}_{3}^{-}\) with the nitrite ion \(\mathrm{NO}_{2}^{-}\). Scandium \(\mathrm{Sc}^{3+}\) will need three nitrite ions to balance the charge, so the formula is \(\mathrm{Sc}\left(\mathrm{NO}_{2}\right)_{3}\).

Key concepts

Understanding Chemical Formulas

A chemical formula is a concise way of expressing the composition of a chemical compound. It provides essential information about the elements present and their relative amounts. In a formula, subscripts are used to show the number of atoms of each element in the compound.
For example, in the chemical formula of water, \( \mathrm{H_2O} \), the subscript '2' indicates there are two hydrogen atoms for every one oxygen atom. Chemical formulas are crucial for understanding how different substances interact, as they reveal the types of atoms involved and how they connect.

• The chemical formula shows the ratio of atoms.
• It provides the identities of the atoms in a compound.
• Subscripts denote the number of each type of atom.

In the context of scandium nitrate, the formula is \( \mathrm{Sc(NO_3)_3} \). This represents one scandium ion combined with three nitrate ions. The subscripts help balance the charges between positively and negatively charged ions, demonstrating the structure and stability of the compound.

The Composition of Scandium Nitrate

Scandium nitrate is a specific type of ternary ionic compound, meaning it consists of three different elements. In this case, scandium nitrate is composed of scandium (Sc), nitrogen (N), and oxygen (O). The formula \( \mathrm{Sc(NO_3)_3} \) indicates that each scandium ion \( \mathrm{Sc^{3+}} \) is paired with three nitrate ions \( \mathrm{NO_3^-} \).
This composition is essential because it ensures charge balance, making the compound electrically neutral. Scandium, with a 3+ charge, requires three 1- charged nitrate ions to balance out its charge.

• Scandium ion: \( \mathrm{Sc^{3+}} \)
• Nitrate ion: \( \mathrm{NO_3^-} \)

These ions combine in a way that neutralizes the compound, which is necessary for forming a stable ionic solid. By understanding the composition of scandium nitrate, students can predict the formula of similar compounds with different ions, as seen with lanthanum nitrate and scandium nitrite.

Principle of Charge Balance in Ionic Compounds

Charge balance is a pivotal concept in chemistry, especially when predicting the formulas of ionic compounds. In ionic compounds, the total positive charge must balance the total negative charge to achieve a neutral compound. This balance ensures that the substance remains stable and bound together.
For example, in scandium nitrate \( \mathrm{Sc(NO_3)_3} \), the scandium ion has a charge of \( +3 \), and each nitrate ion has a charge of \( -1 \). The presence of three nitrate ions balances out the positive charge from scandium, leading to an overall charge of zero. Such balance is intrinsic to all ionic compounds and guides how we write their chemical formulas.

• Total positive charges must equal total negative charges.
• Ionic compounds are electrically neutral.
• Charge balance helps predict the correct formula.

By grasping this concept, students can deduce the chemical formula for other ternary compounds by ensuring that the positive and negative charges are equal, as shown with lanthanum nitrate and scandium nitrite.