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(II) 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; the formulas are PrCl₃ and Pr(NO₃)₂.

Step 1: Understanding the Electron Configuration

Praseodymium has an electron configuration of \([ ext{Xe}] 4f^3 6s^2\). This means in its neutral state, praseodymium has 5 electrons beyond the noble gas xenon configuration. These electrons are: 3 electrons in the 4f orbital and 2 electrons in the 6s orbital.

Step 2: Identifying Electron Removal for 3+ Ion

To form a \(3+\) ion, praseodymium loses three electrons. Typically, the electrons are removed from the outermost shells first. Therefore, praseodymium will lose two electrons from the 6s orbital and one electron from the 4f orbital, leaving the configuration \([ ext{Xe}] 4f^2\).

Step 3: Writing the Formula for Praseodymium(III) Chloride

Praseodymium(III) chloride is formed when praseodymium reacts with hydrochloric acid. Since praseodymium forms a \(3+\) ion and chloride is \(1-\), the formula is \(\text{PrCl}_3\). The balancing of charges ensures the compound is neutral.

Step 4: Writing the Formula for Praseodymium(II) Nitrate

Praseodymium(II) nitrate is formed with a \(2+\) oxidation state, which is indicated in this case, although Pr(II) states are less common. Nitrate is \(1-\), so for a \(2+\) praseodymium ion, the formula is \(\text{Pr(NO}_3)_2\). Charges are balanced with two nitrate ions.

Key Concepts

Lanthanide Series

The lanthanide series consists of 15 metallic elements ranging from Lanthanum \((La)\) to Lutetium \((Lu)\). These elements are found in the f-block of the periodic table. They are known for their unique electronic configurations which involve the filling of 4f orbitals. The lanthanides are also called rare earth elements because they commonly occur together in nature and are difficult to separate due to their similar chemical properties and ionic sizes.

• Lanthanides are typically shiny and silvery-white metals.
• They have high melting and boiling points.
• Most of them are paramagnetic due to unpaired electrons in f-orbitals.

Praseodymium, being part of this series, has special properties linked to its 4f orbitals and electron configuration. This configuration influences its typical chemical behavior, particularly its ability to form various compounds through specific oxidation states.

Oxidation States

Oxidation states refer to the effective charge of an element in a compound and depict its ability to accept, donate, or share electrons. For elements in the lanthanide series, the oxidation state primarily affects how they form compounds.

• Most lanthanides, including praseodymium, often exhibit a +3 oxidation state as it is the most stable.
• However, unlike many other lanthanides, praseodymium can also show a +2 oxidation state.

The electron removal process during oxidation involves removing electrons from the outermost shells. For example, Praseodymium \((\text{Pr})\) forming a 3+ ion requires the removal of electrons from its 6s and 4f orbitals, which rearranges the electron configuration to stabilize the ion.
Understanding oxidation states helps predict reaction outcomes and compound stability, aiding in the formulation of chemical reactions.

Chemical Reactions

Chemical reactions involve the rearrangement of atoms to form new substances. For praseodymium, when reacting with acids like hydrochloric acid (HCl) or nitric acid (HNO₃), the key is to understand how these reactions proceed to form new compounds.
Praseodymium reacts with

• Hydrochloric acid (HCl), losing electrons to form praseodymium(III) chloride \((\text{PrCl}_3)\).
• Nitric acid (HNO₃), potentially losing different numbers of electrons to form praseodymium(II) nitrate \((\text{Pr(NO}_3)_2)\).

These reactions exemplify the metal's ability to change oxidation states. They involve electron transfer, leading to the creation of ionic bonds that stabilize the resulting compounds.

Coordination Compounds

Coordination compounds are complex structures formed by a central metal atom bonded to surrounding molecules or ions, known as ligands. The study of these compounds is essential in understanding advanced chemical interactions beyond simple ionic or covalent bonding.

• Coordination number refers to the number of ligands attached to the metal center.
• Lanthanides can form coordination complexes with a variety of ligands, leveraging their metallic and ionic properties.

Praseodymium, like other lanthanides, can participate in forming such coordination compounds. Its ability to accommodate diverse ligands is due to the availability of vacant orbitals, allowing flexibility in bonding.
Coordination chemistry is crucial in many fields, including catalysis, biochemistry, and material science, allowing for the design of complex materials with specific properties.