Question

$$ \begin{aligned} &\text { Arrange the following species in isoelectronic pairs: }\\\ &\mathrm{O}^{+}, \mathrm{Ar}, \mathrm{S}^{2-}, \mathrm{Ne}, \mathrm{Zn}, \mathrm{Cs}^{+}, \mathrm{N}^{3-}, \mathrm{As}^{3+}, \mathrm{N}, \mathrm{Xe} \end{aligned} $$

Short answer

Isoelectronic pairs are: \( \mathrm{Ar} \) & \( \mathrm{S}^{2-} \), \( \mathrm{Ne} \) & \( \mathrm{N}^{3-} \), \( \mathrm{Zn} \) & \( \mathrm{As}^{3+} \), \( \mathrm{Cs}^{+} \) & \( \mathrm{Xe} \).

Step-by-step solution

Understanding Isoelectronic Pairs

Isoelectronic species are atoms, molecules, or ions that have the same number of electrons. To find isoelectronic pairs from a list of species, you need to count the number of electrons in each species. The species with the same number of total electrons are isoelectronic.

Determine Number of Electrons

Calculate the number of electrons for each species provided. - Oxygen (\( \mathrm{O}^{+} \)): Protons = 8, Electrons = 7- Argon (\( \mathrm{Ar} \)): Protons = 18, Electrons = 18- Sulfide ion (\( \mathrm{S}^{2-} \)): Protons = 16, Electrons = 18- Neon (\( \mathrm{Ne} \)): Protons = 10, Electrons = 10- Zinc (\( \mathrm{Zn} \)): Protons = 30, Electrons = 30- Cesium ion (\( \mathrm{Cs}^{+} \)): Protons = 55, Electrons = 54- Nitride ion (\( \mathrm{N}^{3-} \)): Protons = 7, Electrons = 10- Arsenic ion (\( \mathrm{As}^{3+} \)): Protons = 33, Electrons = 30- Nitrogen (\( \mathrm{N} \)): Protons = 7, Electrons = 7- Xenon (\( \mathrm{Xe} \)): Protons = 54, Electrons = 54.

Grouping Isoelectronic Species

Now, arrange the species into pairs or groups that have the same number of electrons. Based on number of electrons calculated previously:- \( \mathrm{Ar} \) and \( \mathrm{S}^{2-} \): Both have 18 electrons.- \( \mathrm{Ne} \) and \( \mathrm{N}^{3-} \): Both have 10 electrons.- \( \mathrm{Zn} \) and \( \mathrm{As}^{3+} \): Both have 30 electrons.- \( \mathrm{Cs}^{+} \) and \( \mathrm{Xe} \): Both have 54 electrons.

Key concepts

Electrons in Ions

Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge. When an atom loses electrons, it becomes positively charged, known as a cation, such as \(\mathrm{O}^{+}\) or \(\mathrm{Cs}^{+}\). If an atom gains electrons, it becomes negatively charged, resulting in an anion, like \(\mathrm{S}^{2-}\) or \(\mathrm{N}^{3-}\).

The number of electrons differs from the number of protons when atoms become ions. This is key in finding isoelectronic pairs because the charge of an ion directly alters its electron count.

• Positively charged ions (cations) have fewer electrons than the neutral atom.
• Negatively charged ions (anions) have more electrons than the neutral atom.

For example, a neutral \(\mathrm{Ne}\) atom has 10 electrons. When \(\mathrm{N}\) becomes a nitride ion \(\mathrm{N}^{3-}\), it gains three extra electrons, also totaling 10, making it isoelectronic with \(\mathrm{Ne}\).
Understanding how to determine the number of electrons in ions is fundamental for identifying isoelectronic species.

Isoelectronic Pairs

Isoelectronic pairs refer to species, which can be atoms, ions, or molecules, that possess the same number of electrons. Identifying these pairs involves counting the electrons in each species to find matches.

The electron configuration might be identical, but their properties can differ significantly due to their atomic structure and nuclear charge. For instance, although \(\mathrm{Ar}\) and \(\mathrm{S}^{2-}\) each have 18 electrons, they have different chemical and physical properties.

• Important in chemistry for understanding reactivity and bonding.
• Used in predicting the behavior of elements and ions in various conditions.

To find isoelectronic pairs, count the electrons:

• Neon \(\mathrm{Ne}\) and Nitride Ion \(\mathrm{N}^{3-}\): Both have 10 electrons.
• Argon \(\mathrm{Ar}\) and Sulfide Ion \(\mathrm{S}^{2-}\): Both have 18 electrons.
• Zinc \(\mathrm{Zn}\) and Arsenic Ion \(\mathrm{As}^{3+}\): Both have 30 electrons.
• Cesium Ion \(\mathrm{Cs}^{+}\) and Xenon \(\mathrm{Xe}\): Both have 54 electrons.

Atomic Structure

The atomic structure is the framework that describes an atom. It consists of a nucleus made up of protons and neutrons and is surrounded by electrons. Electrons occupy "shells" or energy levels around the nucleus.

The number of protons (atomic number) defines the type of element and remains constant in ions, but electron count can change. For example:

• An Oxygen atom \(\mathrm{O}\) has 8 protons and normally 8 electrons. As \(\mathrm{O}^{+}\), it has 7 electrons.
• Xenon \(\mathrm{Xe}\), a noble gas, naturally has a full outer electron shell with 54 electrons. This same number occurs in the \(\mathrm{Cs}^{+}\) ion when cesium loses one electron.

Electrons play a crucial role in chemical reactions and bonding, while the number of electrons relative to protons affects the charge and behavior of ions.
Understanding the atomic structure helps in identifying how ions form and how they can become isoelectronic with each other.

Ions and Electrons

The relationship between ions and electrons is fundamental for understanding chemistry and atomic interactions. Electrons are vital in forming ions, as the loss or gain of them changes the neutral atom into an ion.

Ions form when atoms seek to achieve a stable electron configuration, typically similar to the nearest noble gas. This might mean gaining electrons to fill an outer shell or losing electrons to empty it.

• Positively charged ions (cations) form by losing electrons.
• Negatively charged ions (anions) form by gaining electrons.

Determining the number of electrons in ions is key in understanding ion behavior and finding isoelectronic pairs. For instance:

• In the exercise, determining the \(\mathrm{Cs}^{+}\) and \(\mathrm{Xe}\) as isoelectronic requires knowing how \(\mathrm{Cs}^{+}\) loses an electron to match the electron count of stable xenon.
• The nature and number of electrons in ions affect the atom's chemical properties and reactions.

By mastering these interactions, students will achieve a deeper comprehension of elemental behavior and ion characteristics.