Question

Write the electron configurations for the following ions, and determine which have noble-gas configurations: (a) \(\mathrm{Co}^{2+}\), (b) \(\mathrm{Sn}^{2+}\), (c) \(\mathrm{Zr}^{4+}\), (d) \(\mathrm{Ag}^{+}\), (e) \(\mathrm{S}^{2-}\).

Short answer

The electron configurations for the given ions are: a) \(\mathrm{Co}^{2+}\): [Ar]3d⁷ b) \(\mathrm{Sn}^{2+}\): [Kr]4d¹0 c) \(\mathrm{Zr}^{4+}\): [Kr] d) \(\mathrm{Ag}^{+}\): [Kr]4d¹0 e) \(\mathrm{S}^{2-}\): [Ne]3s²3p⁶ = [Ar] The ions with noble-gas configurations are \(\mathrm{Zr}^{4+}\) and \(\mathrm{S}^{2-}\).

Step-by-step solution

Write down the ground-state electron configurations for each atom.

First, we need to know the electron configurations of the neutral atoms. The configuration can be found from the periodic table. a) Co (Cobalt, atomic number 27): [Ar]4s²3d⁷ b) Sn (Tin, atomic number 50): [Kr]5s²4d¹0 c) Zr (Zirconium, atomic number 40): [Kr]5s²4d² d) Ag (Silver, atomic number 47): [Kr]5s¹4d¹0 e) S (Sulfur, atomic number 16): [Ne]3s²3p⁴

Determine the electron configurations for the ions.

Now that we have the neutral atom configurations, we can remove or add electrons according to the ion charge. a) \(\mathrm{Co}^{2+}\): Remove 2 electrons, prioritize the 4s shell: [Ar]4s⁰3d⁷ = [Ar]3d⁷ b) \(\mathrm{Sn}^{2+}\): Remove 2 electrons, prioritize the 5s shell: [Kr]5s⁰4d¹0 = [Kr]4d¹0 c) \(\mathrm{Zr}^{4+}\): Remove 4 electrons, prioritize the 5s and 4d shells: [Kr]5s⁰4d⁰ = [Kr] d) \(\mathrm{Ag}^{+}\): Remove 1 electron, prioritize the 5s shell: [Kr]5s⁰4d¹0 = [Kr]4d¹0 e) \(\mathrm{S}^{2-}\): Add 2 electrons to the 3p shell: [Ne]3s²3p⁶

Identify ions with noble-gas configurations.

Now we can compare the ion configurations to the electron configuration of the nearest noble gases. a) \(\mathrm{Co}^{2+}\): [Ar]3d⁷ - not a noble gas configuration b) \(\mathrm{Sn}^{2+}\): [Kr]4d¹0 - not a noble gas configuration c) \(\mathrm{Zr}^{4+}\): [Kr] - noble gas configuration d) \(\mathrm{Ag}^{+}\): [Kr]4d¹0 - not a noble gas configuration e) \(\mathrm{S}^{2-}\): [Ne]3s²3p⁶ = [Ar] - noble gas configuration The ions with noble gas configurations are \(\mathrm{Zr}^{4+}\) and \(\mathrm{S}^{2-}\), as they have electron configurations similar to noble gases.

Key concepts

Noble Gas Configuration

The noble gas configuration is a way of writing the electron configuration of an element that highlights the similarity to the electron arrangement of a noble gas. Noble gases, such as helium (He), neon (Ne), and argon (Ar), are found in group 18 of the periodic table and are known for their full outer electron shells, making them highly stable.
Using the noble gas notation, electron configurations start by noting the noble gas that precedes the element on the periodic table in brackets. This concise form allows us to focus on the valence electrons, which play a significant role in chemical reactions.
For example, sulfur's electron configuration is [Ne]3s²3p⁴. When it gains two electrons to form ext{S}^{2-}, it has the same electronic configuration as argon, a noble gas, thus achieving a stable noble gas configuration. This stability is a common goal in chemical reactions and ion formation.

Ions

Ions are atoms or molecules that have gained or lost one or more electrons, giving them a net electrical charge. This process can result in either positive ions (cations) or negative ions (anions).
When an atom loses electrons and forms a cation, it has more protons than electrons, which results in a positive charge. Common examples include ext{Na}^{+} and ext{Ca}^{2+}.
Conversely, when an atom gains electrons and forms an anion, it gains a negative charge due to having more electrons than protons. Examples of anions include ext{Cl}^{-} and ext{O}^{2-}.
The formation of ions is a crucial concept in chemistry, as it explains the behavior of elements during chemical reactions. Ions are important in many natural processes and technological applications, such as the conduction of electricity in solutions and biological functions.

Electron Removal and Addition

Electron removal and addition are essential processes in forming ions. In electron removal, electrons are taken away from their shells, typically starting from the outermost shell, to form positively charged ions (cations).
For instance, when cobalt loses two electrons to form ext{Co}^{2+}, the electrons are removed mainly from the 4s shell, resulting in the electron configuration [Ar]3d⁷.
In contrast, electron addition involves adding electrons to an atom's outer shells, leading to negatively charged ions (anions).
Sulfur gaining two electrons to become ext{S}^{2-} is an example, and its electron configuration changes from [Ne]3s²3p⁴ to a stable noble gas configuration [Ne]3s²3p⁶.
These changes in electron configurations explain the stability achieved by elements when they reach configurations similar to noble gases, often the motivation behind ion formation.

Atomic Structure

Understanding atomic structure is fundamental to grasping the behavior of elements and their ions. Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in various shells or energy levels.
The number of protons defines the element and is always equal to the atomic number. Electrons are arranged in shells around the nucleus, following rules that dictate the maximum number of electrons each shell can hold.
Electrons fill lower energy (inner) shells first before occupying higher energy (outer) shells. The arrangement of electrons is depicted in the electron configuration, which influences how elements interact with each other.
In ion formation, electron configurations change but the nucleus remains unaffected, ensuring the identity of the element is retained. This behavior is crucial for understanding chemical reactions, bonding, and other properties of matter.