Problem 96 - Chemistry The Central Science In Si Units

Question

Identify a +2 cation that has the following ground state electron configurations: (a) \([\mathrm{Ne}]\) (b) \([\mathrm{Ar}] 3 d^{9}\) (c) \([\mathrm{Xe}] 4 \mathrm{f}^{14} 5 d^{10} 6 s^{2}\).

Step-by-Step Solution

Answer

(a) Mg^{2+}, (b) Cu^{2+}, (c) Pb^{2+}.

Step 1: Understanding the Electron Configuration

To identify the cation, we need to determine what element has the given electron configuration before losing two electrons to become a +2 cation. Electron configuration provides the arrangement of electrons in the atomic orbitals.

Step 2: Analyze Configuration (a)

The configuration \( [\mathrm{Ne}] \) represents the neon electron configuration, which is the configuration for 10 electrons. Since it is a +2 cation, we add 2 electrons to find the neutral atom, giving the configuration of magnesium (12 electrons), which is \[ 1s^2 2s^2 2p^6 3s^2 \]. So, the +2 cation is \( Mg^{2+} \).

Step 3: Analyze Configuration (b)

The configuration \( [\mathrm{Ar}] 3d^9 \) indicates a total of 27 electrons when neutral. Including the 2 electrons removed as it is a +2 cation, it originally had 29 electrons, which corresponds to copper in its neutral state with the configuration \[ [\mathrm{Ar}] 3d^{10} 4s^1 \]. Thus, the +2 cation is \( Cu^{2+} \).

Step 4: Analyze Configuration (c)

The configuration \( [\mathrm{Xe}] 4f^{14} 5d^{10} 6s^2 \) describes an ion with 80 electrons. Considering the +2 state, the neutral atom has 82 electrons. This corresponds to lead, which has the neutral configuration \[ [\mathrm{Xe}] 4f^{14} 5d^{10} 6s^2 6p^2 \]. Hence, the +2 cation is \( Pb^{2+} \).

Key Concepts

Cation Identification

Identifying cations involves understanding their electron configurations, which tell us how many electrons are in each energy level and orbital of an atom. A cation is a positively charged ion formed when an atom loses electrons. The positive charge corresponds to the number of electrons removed. For a +2 cation, two electrons are removed from the neutral atom's total electron count.

• Start by adding the charge number (e.g., +2) to the electron count of the cation's configuration to deduce the original number of electrons in the neutral atom.
• With this electron count, find an element in the periodic table with that configuration.
• This approach allows you to identify the unknown cation based on the electron configuration provided.

The key lies in reversing the electron removal to figure out the element the cation comes from.

Ground State Electron Configuration

The ground state electron configuration is the most stable arrangement of electrons for a given element. It follows the "Aufbau Principle," where electrons fill lower energy orbitals first before moving to higher ones. Each element has a unique ground state configuration that can be represented symbolically.

• Configurations are built starting from the lowest energy orbitals: read as you would a book, left to right, top to bottom in the periodic table.
• Noble gas notation: an efficient shorthand using a noble gas to simplify the notation. For example, \( [\mathrm{Ne}] \) represents the configuration of 10 electrons from neon, allowing you to focus on higher orbitals for heavier elements.
• Each orbital can hold a specific number of electrons: s (2), p (6), d (10), f (14), and this helps in understanding how electrons are distributed in an atom.

Knowing the ground state configuration aids significantly in predicting an element's chemical behavior and its tendency to form certain ions.

Electron Removal Process

The electron removal process explains how atoms transform into cations by losing electrons. When removing electrons, they're taken from the outermost energy levels, often known as valence shells, first. This process directly affects an element’s electron configuration and its stability.

• The removal sequence often follows the opposite order of filling. Generally, electrons from the highest energy orbitals, specifically those in the outermost shells, are removed first.
• In transition metals, electrons in \( s \) orbitals may be removed before those in \( d \) orbitals even though \( d \) orbitals are filled first, due to energy considerations.
• For a +2 cation, two electrons are typically removed, which can change the chemical properties and reactivity of the ion.

The understanding of electron removal and the effect it has on electronic configuration is essential for accurately predicting the formation of cations and their resulting properties.