Problem 20 - General Chemistry: Principles and Modern Applications

Question

Is it possible for two different atoms to be isoelectronic? two different cations? two different anions? a cation and an anion? Explain.

Step-by-Step Solution

Answer

Yes, it is possible for two different atoms, cations, anions, and a cation and an anion to be isoelectronic. All these species can achieve the same electronic configuration and, thus, are considered isoelectronic.

Step 1: Understanding Isoelectronic Species

Isoelectronic species are those which have the same number of electrons or the same electronic configuration. It does not depend on the type of atom or ion, be it an atom, cation, or anion.

Step 2: Comparing Two Different Atoms

As different atoms can share the same electronic configuration when they gain or lose electrons to achieve stable configuration, they can indeed be isoelectronic. For example, neon (a neutral atom) and fluoride ion (F-) are isoelectronic as they both have 10 electrons and share the same electronic configuration.

Step 3: Comparing Two Different Cations

Similarly, two different cations can also be isoelectronic. Sodium ion (Na+) and magnesium ion (Mg2+) being examples, as they both have 10 electrons after losing electrons.

Step 4: Comparing Two Different Anions

Two different anions can also be isoelectronic. For instance, sulfide ion (S2-) and chloride ion (Cl-) both have 18 electrons after gaining electrons to obtain stable configuration.

Step 5: Comparing a Cation and an Anion

A cation and an anion can also be isoelectronic. An example is that of potassium ion (K+) and chloride ion (Cl-), both of which have 18 electrons.

Key Concepts

Electronic Configuration

The term "electronic configuration" refers to the arrangement of electrons in the orbitals of an atom or ion. It provides insight into the chemical behavior of elements. Electrons fill energy levels based on specific rules, such as the Aufbau principle and Hund's rule, which dictate the order of filling. This configuration impacts how atoms interact with others.

• Electrons occupy available orbitals in increasing order of energy.
• Stable electronic configurations often resemble the noble gases, which have full outer electron shells.
• Atoms or ions with the same electronic configuration are called isoelectronic species.

Understanding electronic configuration helps explain why isoelectronic species behave similarly in chemical reactions. They possess the same arrangement of electrons and therefore have comparable chemical properties.

Cations and Anions

Cations and anions are types of ions that are formed when atoms either lose or gain electrons, respectively. A cation is a positively charged ion, while an anion is negatively charged. The formation of these ions leads to the creation of isoelectronic species.

• Cations: These are formed when an atom loses one or more electrons. As a result, the cation has more protons than electrons, giving it a positive charge.
• Anions: These occur when an atom gains electrons, resulting in more electrons than protons, thus a negative charge.

Examples of isoelectronic species include sodium ion (\( \text{Na}^+ \) ) and magnesium ion (\( \text{Mg}^{2+} \) ), which both have 10 electrons, just like the neon atom. Similarly, the chloride ion (\( \text{Cl}^- \) ) and sulfide ion (\( \text{S}^{2-} \) ) share 18 electrons, akin to the argon atom.

Electron Gain and Loss

Atoms strive for stability, often achieved by having a full outer shell of electrons. This pursuit leads to gaining or losing electrons.

• When atoms gain electrons, they become anions with a negative charge.
• When atoms lose electrons, they become cations with a positive charge.

Electron gain and loss result in atoms achieving a stable electronic configuration, often similar to the nearest noble gas. For example, a chlorine atom gains one electron to become \( \text{Cl}^- \) , achieving an electron count identical to argon. Conversely, a sodium atom loses one electron, forming \( \text{Na}^+ \) , and mirrors the electron configuration of neon.

This sharing of the same number of electrons between different species underscores the concept of isoelectronic species. Such species, whether they are atoms, cations, or anions, illustrate how electron gain and loss impact chemical stability and reactivity.