Which of the following species are isoelectronic with each other? \(\mathrm{C}, \mathrm{Cl}^{-}, \mathrm{Mn}^{2+}, \mathrm{B}^{-}, \mathrm{Ar}, \mathrm{Zn}, \mathrm{Fe}^{3+}, \mathrm{Ge}^{2+}\)

Understanding the atomic number of an element is fundamental to the study of chemistry. The atomic number, often depicted on the periodic table, is the number that defines each element. In essence, it represents the number of protons found in the nucleus of an atom.

For instance, carbon (C) has an atomic number of 6, meaning every carbon atom has 6 protons. This also means that a neutral carbon atom would have 6 electrons to balance its electric charge.

In a neutral atom, the atomic number is also equal to the number of electrons, which are the primary players in chemical reactions and bonding. Hence, the atomic number not only tells us about the identity of the element but also provides insight into its chemical behavior.

Ions are atoms that have gained or lost electrons, resulting in a net electric charge. Loss of electrons produces a positively charged ion (cation), while gaining electrons results in a negatively charged ion (anion).

Charge and Electron Count

The charge on an ion directly impacts the number of electrons present. For example, if a chlorine atom (with an atomic number of 17) gains an electron, it becomes a chloride ion (Cl-) with 18 electrons. This extra electron gives it a -1 charge.

Similarly, when a manganese atom (Mn) loses two electrons, it forms a Mn²⁺ cation with 23 electrons — two less than the neutral atom, aligning with its +2 charge. Understanding how to calculate the change in electron count due to ionization is critical when comparing the properties of elements and their ions.

The electron configuration of an atom describes the distribution of electrons among the orbitals of an atom. While the atomic number tells us the total number of electrons in a neutral atom, the electron configuration illustrates how these electrons are arranged.

For atoms or ions that have the same number of electrons, we say they are isoelectronic. Despite different numbers of protons (atomic numbers), isoelectronic species have the same electron configurations and similar chemical properties.

Determining Isoelectronic Species

To determine if two species are isoelectronic, we examine their electron configurations or simply compare their total electron count after considering any charges. For instance, zinc (Zn) with 30 electrons in a neutral state shares the same number of electrons with germanium ion (Ge²⁺), which starts with 32 electrons but loses two due to its +2 charge, making them isoelectronic.