Question

There are two elements in the transition-metal series Sc through Zn that have four unpaired electrons in their \(2+\) ions. Identify them.

Short answer

Chromium (Cr²⁺) and Iron (Fe²⁺) have four unpaired electrons.

Step-by-step solution

Review the Transition Metal Series

The transition metal series from Scandium (Sc) to Zinc (Zn) includes the elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. These elements have partially filled d subshells both as atoms and as ions, which contribute to their unique properties.

Understand Unpaired Electron Configuration

Unpaired electrons are those that do not share an electron in their specific orbital. Transition metals typically have partially filled d orbitals and may lose electrons from their s orbital first when forming cations.

Consider the Electron Configuration of Ions

For each element, upon losing two electrons to form a 2+ ion, it is important to consider where these electrons are coming from (typically from the s orbital) and what's left in the d orbitals. We are looking for ions with exactly four unpaired electrons in their d orbitals.

Calculate Electronic Configuration for Each 2+ Ion

Determine the electronic configurations for the 2+ ions of each element in the series. You will subtract electrons first from the 4s orbital, followed by the 3d, then check the resulting configuration for unpaired electrons.

Identify Ions with Four Unpaired Electrons

Calculate or look through the configurations to determine which ions have four unpaired electrons: - Chromium (Cr): [Ar] 3d⁴ - Iron (Fe): [Ar] 3d⁶ Both Cr²⁺ and Fe²⁺ have configurations with exactly four unpaired electrons.

Key concepts

Unpaired Electrons

Unpaired electrons are quite interesting in the world of chemistry, especially when it comes to transition metals. In simple terms, unpaired electrons are those that do not have a matching counterpart in the same orbital.
This makes them crucial in determining the magnetic properties of an element. When discussing unpaired electrons within transition metals, one should know that these elements use their d orbitals. Here, the distribution of these electrons, whether paired or unpaired, affects the metal's behavior and properties. For example:

• If all electrons are paired, the substance tends to be diamagnetic, which means it's not attracted to a magnetic field.
• If there are unpaired electrons, the substance is paramagnetic and will be attracted to a magnetic field.

In the case of this exercise, Chromium (Cr) and Iron (Fe) have 2+ ions that specifically possess four unpaired electrons in their d orbitals, affecting their magnetic behavior.

Electronic Configuration

Electronic configurations provide a map of how electrons are distributed in an atom's orbitals. Transition metals have unique configurations because of their partially filled d orbitals. This can be complex, as these elements have electrons that can fill the 4s orbital before starting with the 3d. The general approach for electronic configurations is to follow the Aufbau principle, which tells us to fill from lower to higher energy levels:

• First, fill the 1s orbital, then 2s, 2p, 3s, and so on until reaching the 4s orbital.
• After 4s is filled, electrons enter the 3d orbitals, giving transition metals their characteristic properties.

This electron distribution helps us understand how elements form ions, particularly how electrons get removed when they become cations. Take care to subtract electrons correctly for cations like Cr²⁺ and Fe²⁺, focusing on the resulting d orbitals for unpaired electrons.

Transition Metals

Transition metals are found in the central block of the periodic table, specifically from Scandium (Sc) to Zinc (Zn). These metals are known for their ability to form various oxidation states and colorful compounds due to their d orbital electrons. What makes transition metals special?

• They can form stable ions with different charges, often losing s and then d orbital electrons.
• They have partially filled d orbitals, which can lead to interesting chemical and physical properties.
• They're often used as catalysts due to their ability to lend and take back electrons during reactions.

In our specific task, transition metals' ability to form cations with specific numbers of unpaired electrons is of high importance, focusing on Cr and Fe.

Cations

Cations are positively charged ions, which occur when an atom loses one or more electrons. This process is essential for transition metals as it often involves the loss of electrons from the outermost s orbital first, and then from the d orbitals. Key points about cations:

• Transition metals can form multiple cations with different charges, such as 2+, 3+, etc.
• The 2+ charge often results from the loss of two electrons from the s orbital.
• This loss affects the electronic configuration and can influence the number of unpaired electrons.

In this exercise, both Chromium (Cr) and Iron (Fe) form 2+ cations with noteworthy unpaired electrons in their electronic configuration. This property is crucial in understanding their chemical and physical properties, such as magnetism.