Question

Refer to the periodic table and write the predicted electron configuration for each of the following positive ions using core notation: (a) \(\mathrm{Mg}^{2+}\) (b) \(K^{+}\) (c) \(\mathrm{Fe}^{2+}\) (d) \(Z r^{2+}\)

Short answer

Mg²⁺: [Ne], K⁺: [Ar], Fe²⁺: [Ar] 3d⁶, Zr²⁺: [Kr] 4d².

Step-by-step solution

Understand the Concept of Electron Configuration

Electron configuration refers to the distribution of electrons in an atom's orbitals. For ions, electrons are added (for negative ions) or removed (for positive ions) based on their charge. When writing electron configurations for positive ions, we remove electrons from the neutral atom's configuration.

Identify Neutral Atom Electron Configurations

Locate each element on the periodic table to determine the electron configuration for the neutral atom: - Mg: Atomic number 12, configuration: [Ne] 3s² - K: Atomic number 19, configuration: [Ar] 4s¹ - Fe: Atomic number 26, configuration: [Ar] 3d⁶ 4s² - Zr: Atomic number 40, configuration: [Kr] 4d² 5s²

Remove Electrons for Ion Charge

For each ion, remove the appropriate number of electrons from the neutral atom:- \(\text{Mg}^{2+}:\) Remove 2 electrons from [Ne] 3s², resulting in [Ne].- \(\text{K}^{+}:\) Remove 1 electron from [Ar] 4s¹, resulting in [Ar].- \(\text{Fe}^{2+}:\) Remove 2 electrons; typically from the 4s and then the 3d, resulting in [Ar] 3d⁶.- \(\text{Zr}^{2+}:\) Remove 2 electrons from 5s², resulting in [Kr] 4d².

Write the Electron Configurations for Each Ion

Combine the findings from step 3 to express the electron configurations of the ions:- \(\text{Mg}^{2+}: [\text{Ne}]\)- \(\text{K}^{+}: [\text{Ar}]\)- \(\text{Fe}^{2+}: [\text{Ar}] 3d^6\)- \(\text{Zr}^{2+}: [\text{Kr}] 4d^2\)

Key concepts

Periodic Table

The periodic table is a fundamental tool in chemistry that organizes all known elements in a structured format. Each element is placed in the table according to its atomic number, which is the number of protons in its nucleus.
This arrangement helps us predict the properties and behaviors of the elements, including how they will bond with other elements to form compounds.
The periodic table is divided into several blocks based on the electron configuration of the elements, including the s, p, d, and f blocks. This determines the element's position in the periodic table and helps us understand its chemical reactivity.

• The s-block includes the first two groups, featuring elements with outer electrons in s orbitals.
• The p-block contains groups 13-18, with outer electrons in p orbitals.
• The d-block, also known as the transition metals, includes elements with outer electrons in d orbitals.

By understanding the structure of the periodic table, we can easily determine the electron configurations of neutral atoms and their ions.

Positive Ions

Positive ions, or cations, are atoms that have lost electrons, resulting in a net positive charge. The formation of positive ions usually occurs when metals lose electrons to achieve a more stable electron arrangement. This process is driven by the element's desire to achieve a full outer shell, similar to that of noble gases.
When writing electron configurations for positive ions, electrons are typically removed from the highest energy level or outermost shell.
Key points to remember include:

• Electrons are removed starting from the highest energy orbital, which is often the outermost shell.
• The number of electrons lost corresponds to the charge of the ion. For example, Mg losing two electrons forms \( \text{Mg}^{2+} \).
• Transition metals may lose electrons from s and d orbitals, affecting their oxidation states and reactivity.

Understanding positive ions is crucial in predicting how elements will interact in chemical reactions.

Core Notation

Core notation is a shorthand form of electron configuration that simplifies the representation of the inner shell electrons. Instead of writing out every single electron configuration, core notation allows us to focus on the valence electrons, which are responsible for an element's chemical properties.
This notation uses a noble gas symbol in brackets to represent the inner shell, or "core" electrons that are not involved in bonding. For example, the electron configuration of magnesium (Mg) can be expressed as \( [\text{Ne}] \, 3s^2 \), indicating that its inner electrons match those of neon.
This method is widely used because:

• It simplifies the process of writing electron configurations.
• Emphasizes the valence electrons, which participate in bonding and reactions.
• Reduces errors by focusing on the most important electrons for chemistry related studies.

Core notation is especially helpful when dealing with elements that have a large number of inner electrons, making the electron configuration manageable and understandable.

Atomic Number

The atomic number of an element is a fundamental property that defines the chemical identity of that element. It represents the number of protons found in the nucleus of an atom, which in turn equals the number of electrons in a neutral atom.
The atomic number determines an element's position on the periodic table and provides important information about its electron configuration. For example, magnesium has an atomic number of 12, which means it has 12 protons and, in its neutral state, 12 electrons as well.
Understanding atomic numbers is essential for:

• Identifying elements and predicting their chemical behaviors.
• Determining the electron configuration for both neutral atoms and their ions.
• Calculating the number of electrons needed to form positive or negative ions.

With the atomic number, we can unlock many of the secrets to understanding each element's unique properties and reactions.