Question

Which neutral atom is isoelectronic with each of the following ions? \(\mathrm{H}^{-}, \mathrm{Ca}^{2+}, \mathrm{In}^{3+}, \mathrm{Ge}^{2+}\)

Short answer

The neutral atoms isoelectronic with the given ions are: \(\mathrm{He}\) for \(\mathrm{H}^{-}\), \(\mathrm{Ar}\) for \(\mathrm{Ca}^{2+}\), \(\mathrm{Pd}\) for \(\mathrm{In}^{3+}\), and \(\mathrm{Zn}\) for \(\mathrm{Ge}^{2+}\).

Step-by-step solution

Find the number of electrons for each ion

To determine which neutral atom is isoelectronic with each ion, we must first find the number of electrons for the given ions. To do this, we need the atomic number (number of protons) of each element and the ion's charge. An ion's atomic number minus its charge gives the number of electrons. From the periodic table, we have the atomic numbers for H (Hydrogen)=1, Ca (Calcium)=20, In (Indium)=49, and Ge (Germanium)=32.

Determine the neutral atom isoelectronic to \(\mathrm{H}^{-}\)

For \(\mathrm{H}^{-}\), the charge is -1. Therefore, the number of electrons is 1 (atomic number) - (-1) = 2. A neutral atom with 2 electrons is Helium (He). Therefore, \(\mathrm{He}\) is isoelectronic with \(\mathrm{H}^{-}\).

Determine the neutral atom isoelectronic to \(\mathrm{Ca}^{2+}\)

For \(\mathrm{Ca}^{2+}\), the charge is +2. Therefore, the number of electrons is 20 (atomic number) - 2 = 18. A neutral atom with 18 electrons is Argon (Ar). Therefore, \(\mathrm{Ar}\) is isoelectronic with \(\mathrm{Ca}^{2+}\).

Determine the neutral atom isoelectronic to \(\mathrm{In}^{3+}\)

For \(\mathrm{In}^{3+}\), the charge is +3. Therefore, the number of electrons is 49 (atomic number) - 3 = 46. A neutral atom with 46 electrons is Palladium (Pd). Therefore, \(\mathrm{Pd}\) is isoelectronic with \(\mathrm{In}^{3+}\).

Determine the neutral atom isoelectronic to \(\mathrm{Ge}^{2+}\)

For \(\mathrm{Ge}^{2+}\), the charge is +2. Therefore, the number of electrons is 32 (atomic number) - 2 = 30. A neutral atom with 30 electrons is Zinc (Zn). Therefore, \(\mathrm{Zn}\) is isoelectronic with \(\mathrm{Ge}^{2+}\). From this analysis, we found that: 1. \(\mathrm{He}\) is isoelectronic with \(\mathrm{H}^{-}\) 2. \(\mathrm{Ar}\) is isoelectronic with \(\mathrm{Ca}^{2+}\) 3. \(\mathrm{Pd}\) is isoelectronic with \(\mathrm{In}^{3+}\) 4. \(\mathrm{Zn}\) is isoelectronic with \(\mathrm{Ge}^{2+}\)

Key concepts

Electron Configuration

Electron configuration refers to the arrangement of electrons in an atom's orbitals. Electrons are distributed among various energy levels and sublevels, following a specific order that follows the Pauli Exclusion Principle, Hund's Rule, and the Aufbau Principle. This configuration determines the chemical behavior and characteristics of the element.
Each element's electron configuration can be determined by its position on the periodic table. For instance:

• Hydrogen ( \(\mathrm{H}\)) normally has the configuration \(1s^{1}\).
• For helium ( \(\mathrm{He}\)), it is \(1s^{2}\) as helium has two electrons.

To find isoelectronic species, we compare such electron configurations to see if different species (atoms or ions) have the same number of electrons in the same configuration.

Periodic Table

The periodic table is an arrangement of elements in order of increasing atomic number, which corresponds to the number of protons in an element's nucleus. It organizes elements into rows called periods and columns called groups that reflect recurring chemical properties.
Key concepts:

• Elements in the same group often have similar chemical properties.
• The location of an element on the table helps predict its electron configuration.
• Noble gases, like Argon ( \(\mathrm{Ar}\)), are located in the far-right column and are known for having full valence shells, making them stable and often isoelectronic with certain ions.

Atomic Number

The atomic number of an element tells you the number of protons found in its nucleus. This number is crucial because it defines the identity of the element. For a neutral atom, the atomic number also represents the number of electrons.

• For instance, hydrogen ( \(\mathrm{H}\)) has an atomic number of 1, meaning it has one proton and, in its neutral state, one electron.
• Similarly, calcium ( \(\mathrm{Ca}\)) has an atomic number of 20, meaning 20 protons and 20 electrons in a neutral state.

This concept helps us determine the number of electrons in ions by adjusting for the charge.

Ions

Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge. If an atom loses electrons, it becomes positively charged (cation), and if it gains electrons, it forms a negatively charged ion (anion).
The charge of an ion indicates how many electrons have been lost or gained:

• For \(\mathrm{H}^{-}\), a hydrogen ion gains one electron, resulting in two electrons total - making it isoelectronic with helium.
• \(\mathrm{Ca}^{2+}\) has lost two electrons, thus having 18 electrons, matching the electron count of argon.

Understanding ions is essential for identifying isoelectronic species, as the number of electrons determines the electron configuration, influencing chemical properties and behavior.