Problem 117 - Chemistry Matter and Change

Question

Apply Praseodymium is a lanthanide element that reacts with hydrochloric acid, forming praseodymium(III) chloride. It also reacts with nitric acid, forming praseodymium(III) nitrate. Praseodymium has the electron configuration \([\mathrm{Xe}] 4 \mathrm{f}^{3} 6 \mathrm{s}^{2}\) a. Examine the electron configuration, and explain how praseodymium forms a \(3+\) ion. b. Write the correct formulas for both compounds formed by praseodymium.

Step-by-Step Solution

Answer

Praseodymium forms a 3+ ion by losing 3 electrons from the 4f and 6s orbitals to achieve a stable electron configuration like Xenon. The compounds formed by praseodymium with hydrochloric and nitric acids are Praseodymium(III) chloride, \(PrCl_3\), and Praseodymium(III) nitrate, \(Pr(NO_3)_3\), respectively.

Step 1: Examine the electron configuration and explain how praseodymium forms a 3+ ion

Praseodymium has the electron configuration \([\mathrm{Xe}] 4 \mathrm{f}^{3} 6 \mathrm{s}^{2}\). To achieve a stable electron configuration, this element will lose 3 electrons from the 4f and 6s orbitals. In this process, it will form a 3+ ion with the electron configuration \([\mathrm{Xe}]\), achieving the same electron configuration as the noble gas Xenon, which is considered a stable electron configuration.

Step 2: Write the formula for the compound formed by praseodymium with hydrochloric acid

Praseodymium reacts with hydrochloric acid, which has the formula HCl. The praseodymium ion formed is \(Pr^{3+}\) and the chloride ion from hydrochloric acid is \(Cl^-\). To create a neutral compound, three chloride ions are needed to balance the charge of the praseodymium ion. Therefore, the correct formula for the compound formed by praseodymium with hydrochloric acid is \(PrCl_3\), called Praseodymium(III) chloride.

Step 3: Write the formula for the compound formed by praseodymium with nitric acid

Praseodymium reacts with nitric acid, which has the formula HNO_3. The praseodymium ion formed is \(Pr^{3+}\) and the nitrate ion from nitric acid is \(NO_3^-\). To create a neutral compound, three nitrate ions are needed to balance the charge from the praseodymium ion. Therefore, the correct formula for the compound formed by praseodymium with nitric acid is \(Pr(NO_3)_3\), called Praseodymium(III) nitrate.

Key Concepts

Lanthanide Elements

Praseodymium belongs to a unique group of elements known as the lanthanides. These elements are located in the f-block of the periodic table and are often referred to as rare earth elements.
While they are not as rare as the name suggests, they are essential for various technological applications.
Lanthanides share several common properties:

• They are typically shiny and silvery-white.
• Most have high melting and boiling points.
• They are known for their ability to produce magnetic properties.

Praseodymium, like other lanthanides, shows a +3 oxidation state, which is common among these elements, making them relatively stable when forming compounds.

Electron Configuration

The electron configuration of praseodymium is given by \([\mathrm{Xe}] 4 \mathrm{f}^{3} 6 \mathrm{s}^{2}\)\. This notation tells us the arrangement of electrons in the atom's orbitals.
Understanding electron configuration is crucial because it determines how an element will interact with other substances. Praseodymium has:

• Three electrons in the 4f subshell.
• Two electrons in the 6s subshell.

When praseodymium forms a 3+ ion, it loses three electrons. The loss includes the two 6s electrons and one from the 4f electrons.
By doing so, praseodymium achieves the electron configuration of xenon, which is chemically stable because of filled energy levels.

Chemical Reactions with Acids

When praseodymium reacts with acids like hydrochloric acid (HCl) and nitric acid (HNO₃), it forms ionic compounds.
These reactions are typical for metals, where the metal gives up electrons to form a positive ion. For hydrochloric acid:

• Praseodymium forms Praseodymium(III) chloride, \(PrCl_3\)\.
• This compound results from praseodymium losing three electrons to form a 3+ ion and combining with three chloride ions.

For nitric acid:

• Praseodymium reacts to form Praseodymium(III) nitrate, \(Pr(NO_3)_3\)\.
• Here, three nitrate ions combine with one Pr³⁺ ion to create a neutral compound.

Ionic Compounds

Ionic compounds are made from positive and negative ions that attract each other due to their opposite charges.
This electrostatic attraction is what keeps the compound together. Using praseodymium's reaction with acids as an example:

• Pr³⁺ is the positive ion from praseodymium.
• Cl⁻ and NO₃⁻ are negative ions from hydrochloric and nitric acids respectively.

In these reactions, each praseodymium ion associates with three negative ions. This ensures the overall charge of the compound is zero, making it stable.
Such ionic compounds are often solid and have high melting points. They can conduct electricity when dissolved in water due to the movement of ions.