Question

Identify two ions that have the following ground-state electron configurations: (a) \([\mathrm{Ar}]\), (b) \([\mathrm{Ar}] 3 d^{5}\), (c) \([\mathrm{Kr}] 5 s^{2} 4 d^{10}\).

Short answer

The ions with the given ground-state electron configurations are: (a) Ca\(^{2+}\) with configuration \([\mathrm{Ar}]\), (b) V\(^{2+}\) with configuration \([\mathrm{Ar}] 3 d^{5}\), and (c) Cd\(^{2+}\) with configuration \([\mathrm{Kr}] 5 s^{2} 4 d^{10}\).

Step-by-step solution

Identify the elements from the given configurations

In order to determine which ions have the ground-state electron configurations mentioned, let's first identify the corresponding elements. The abbreviations – Ar and Kr – in the given electron configurations refer to the noble gases Argon (Ar) and Krypton (Kr), respectively. Let's note the respective atomic numbers of these noble gases: Argon: \( Z = 18 \) (18 electrons) Krypton: \( Z = 36 \) (36 electrons) Now, starting from these noble gases, let's determine the elements associated with each configuration.

Determine the ions based on the given electron configurations

(a) \([\mathrm{Ar}]\): This configuration is the same as that of Argon, which has 18 electrons. The isoelectronic ion of Argon with the same configuration will have 18 electrons. An ion can have 18 electrons if it gains_3_ electrons (if it's a negative ion) or loses some electrons (if it's a positive ion). Let's determine an ion that can fit this description. Calcium (Ca) has an atomic number of \( Z = 20 \). When Ca loses 2 electrons, it forms the ion Ca\(^{2+}\), which has the same electron configuration as Argon: \( Ca^{2+}: [\mathrm{Ar}] \) (b) \([\mathrm{Ar}] 3 d^{5}\): This configuration has 5 more electrons than Argon which has 18 electrons. Therefore, it is associated with the element having 23 electrons. Vanadium (V) has an atomic number of \( Z = 23 \) (23 electrons). When V loses 2 electrons, it forms the ion V\(^{2+}\) with the following electron configuration: \( V^{2+}: [\mathrm{Ar}] 3d^5\) (c) \([\mathrm{Kr}] 5 s^{2} 4 d^{10}\): This configuration has 12 more electrons than Krypton, which has 36 electrons. Therefore, it is associated with the element having 48 electrons. Cadmium (Cd) has an atomic number of \( Z = 48 \) (48 electrons) and has the electron configuration of \( [\mathrm{Kr}] 5 s^{2} 4 d^{10}\). When Cd loses 2 electrons, it forms the ion Cd\(^{2+}\), which has the given electron configuration: \( Cd^{2+}: [\mathrm{Kr}] 5s^2 4d^10 \) Thus, the ions that have the given ground-state electron configurations are: (a) Ca\(^{2+}\) (b) V\(^{2+}\) (c) Cd\(^{2+}\)

Key concepts

Ions

Ions are atoms or molecules that have gained or lost one or more electrons, resulting in a net electric charge. This loss or gain of electrons gives the ion different properties compared to its neutral atom.
- **Cations:** These are positively charged ions, formed when an atom loses electrons. For example, a sodium atom becomes a sodium ion, Na⁺, by losing one electron.
- **Anions:** These are negatively charged ions, formed when an atom gains electrons. Chlorine atom gains an electron to become chloride ion, Cl⁻.

The formation of ions is crucial in many chemical reactions and is responsible for the conductivity of substances in molten or dissolved states. Understanding ions is essential for exploring the behavior of elements and their compounds in various chemical contexts.

Noble Gases

Noble gases are a group of elements found in Group 18 of the periodic table, including helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These gases are noted for their lack of reactivity under normal conditions.

• **Full Electron Shells:** Noble gases have complete valence electron shells, which make them very stable and non-reactive.
• **Inert Nature:** Their lack of chemical reactivity is due to the stability of their electron arrangements.
• **Applications:** Despite their inertness, noble gases have important applications, including lighting (neon lights) and cryogenics (liquid helium).

Their stable electron configurations serve as a model for understanding electron configuration in other elements, especially during the formation of ions aiming to achieve a noble gas configuration.

Isoelectronic

The term "isoelectronic" refers to different atoms, ions, or molecules that have the same number of electrons or the same electronic structure. This concept is especially useful when comparing ions and understanding their electron configurations.

• **Equal Electron Count:** Isoelectronic species must have the same number of electrons. For instance, N⁻³, O⁻², and F⁻ are isoelectronic with neon, all having 10 electrons.
• **Chemical and Physical Similarity:** Isoelectronic species often exhibit similar chemical and physical characteristics due to their similar electronic configurations.
• **Application:** Recognizing isoelectronic ions helps predict bonding and reactivity in various chemical processes.

Understanding isoelectronic relationships is essential in the study of chemical bonding and molecular geometry.

Atomic Number

The atomic number of an element, symbolized as Z, represents the number of protons in the nucleus of an atom. This number uniquely identifies a chemical element. It also determines the element's position in the periodic table and its chemical properties.
- **Defines Element Identity:** Each element has a unique atomic number and thus a unique identity.
- **Electron Count in Neutral Atoms:** In neutral atoms, the atomic number equals the total number of electrons, dictating the atom’s electron configuration.
- **Periodic Table Arrangement:** Elements are arranged in ascending order of atomic number in the periodic table. This arrangement underlies the periodic law, which states that the properties of elements are periodic functions of their atomic numbers.

Understanding atomic numbers is crucial for grasping concepts like electron configuration and predicting the chemical behavior of elements.