Question

Among the following ions, several pairs are isoelectronic. Identify these pairs. \(\mathrm{Fe}^{2+}, \mathrm{Sc}^{3+}, \mathrm{Ca}^{2+}, \mathrm{F}^{-}\) \(\mathrm{Co}^{2+}, \mathrm{Co}^{3+}, \mathrm{Sr}^{2+}, \mathrm{Cu}^{+}, \mathrm{Zn}^{2+}, \mathrm{Al}^{3+}.\)

Short answer

The isoelectronic pairs are (\(\mathrm{Fe}^{2+}\), \(\mathrm{Co}^{3+}\)), (\(\mathrm{Sc}^{3+}\), \(\mathrm{Ca}^{2+}\)), (\(\mathrm{F}^{-}\), \(\mathrm{Al}^{3+}\)) and (\(\mathrm{Cu}^{+}\), \(\mathrm{Zn}^{2+}\)).

Step-by-step solution

Determine the Number of Electrons in Each Ion

By summing the atomic number and the charge of the ions, the total number of electrons in each ion can be determined. Use the periodic table to find the atomic number of each element. For example, the atomic number of Fe is 26. Since the ion is \(\mathrm{Fe}^{2+}\), it has lost 2 electrons, so it has 24 electrons in total.

Repeat for All Ions

Apply the same process to all of the ions: \(\mathrm{Sc}^{3+}\) has 18 electrons, \(\mathrm{Ca}^{2+}\) has 18 electrons, \(\mathrm{F}^{-}\) has 10 electrons, \(\mathrm{Co}^{2+}\) has 25 electrons, \(\mathrm{Co}^{3+}\) has 24 electrons, \(\mathrm{Sr}^{2+}\) has 36 electrons, \(\mathrm{Cu}^{+}\) has 28 electrons, \(\mathrm{Zn}^{2+}\) has 28 electrons and \(\mathrm{Al}^{3+}\) has 10 electrons.

Identify Isoelectronic Pairs

Two ions are isoelectronic if they have the same number of electrons. From the calculations carried out, the isoelectronic pairs can therefore be identified as (\(\mathrm{Fe}^{2+}\), \(\mathrm{Co}^{3+}\)), (\(\mathrm{Sc}^{3+}\), \(\mathrm{Ca}^{2+}\)), (\(\mathrm{F}^{-}\), \(\mathrm{Al}^{3+}\)) and (\(\mathrm{Cu}^{+}\), \(\mathrm{Zn}^{2+}\)).

Key concepts

Electron Configuration

Electron configuration refers to the arrangement of electrons in the orbital structure of an atom. Electrons are arranged based on increasing energy levels in a pattern dictated by subshells and orbitals. Understanding electron configurations allows us to predict the chemical and physical properties of an element.
For instance, the electron configuration of an atom like iron (Fe) with 26 electrons in its neutral state would be written as: - 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶. When ions are formed, electrons are typically lost or gained from the outermost energy levels, which affects their configuration. As iron becomes \(\text{Fe}^{2+}\), it loses 2 electrons from the 4s and 3d levels, resulting in 24 electrons. This highlights how electron configurations change based on ionic states, which is crucial for identifying isoelectronic ions.

Periodic Table

The periodic table is a visual representation grouping the elements based on their atomic number, electron configurations, and recurring chemical properties. Positioned in rows and columns, it serves as an invaluable tool for predicting element behavior and interactions.
Each element's position on the table dictates its number of electrons, and thus its starting point for electron configuration. For example:- The atomic number of Calcium (Ca) is 20, providing its baseline of 20 electrons when neutral.- Its position in Group 2 indicates it forms a \(\text{Ca}^{2+}\) ion, losing 2 electrons to result in 18 electrons. Utilizing the periodic table allows students to quickly identify atomic numbers, unravel electron configurations and, essentially, spot potential isoelectronic scenarios across different ions.

Ionic Charge

Ionic charge is determined by the loss or gain of electrons by an atom, leading to cations (positively charged) or anions (negatively charged). Understanding the charge helps us to deduce electron configurations when identifying the total electrons present.
Metals, such as iron (Fe), lose electrons easily to form positive ions. In the case of \(\text{Fe}^{2+}\), the charge is +2 as it has lost two electrons compared to its neutral state. Nonmetals, like fluorine (F), gain electrons resulting in negative ions. For \(\text{F}^{-}\), gaining one electron gives a charge of -1 from its neutral atom state.
Recognizing ionic charges is key when exploring isoelectronic pairs where different ions share the same electron count. This understanding bridges electron configuration knowledge and periodic table placement for a comprehensive grasp of element behavior in ionic form.