Question

Write the electron configuration for each of the following ions, and determine which ones possess noble-gas configurations: (a) \(\mathrm{Sr}^{2+},(\mathbf{b}) \mathrm{Ti}^{2+},(\mathbf{c}) \mathrm{Se}^{2-},(\mathbf{d}) \mathrm{Ni}^{2+},(\mathbf{e}) \mathrm{Br}^{-}\) \((\mathbf{f}) \mathrm{Mn}^{3+}\)

Short answer

The electron configurations for the given ions are: (a) Sr²⁺: [Kr] (b) Ti²⁺: [Ar] 3d² (c) Se²⁻: [Ar] 4s²3d¹⁰4p⁶ (d) Ni²⁺: [Ar] 3d⁶ (e) Br⁻: [Ar] 4s²3d¹⁰4p⁶ (f) Mn³⁺: [Ar] 3d⁴ The ions Sr²⁺, Se²⁻, and Br⁻ possess noble-gas configurations (Kr).

Step-by-step solution

Identify electron configurations for given ions

To find the electron configuration for a given ion, we need to first have its neutral atom's electron configuration. We can easily do this by looking at the atomic number on the periodic table. Then, we'll add or remove the corresponding number of electrons according to the ion's charge. Here are the electron configurations for the given ions: (a) Sr²⁺: The neutral Sr atom's electron configuration is [Kr] 5s². Since Sr²⁺ has lost two electrons, its electron configuration is [Kr]. (b) Ti²⁺: The neutral Ti atom's electron configuration is [Ar] 4s²3d². If Ti²⁺ has lost two electrons, its electron configuration is [Ar] 3d². (c) Se²⁻: The neutral Se atom's electron configuration is [Ar] 4s²3d¹⁰4p⁴. Since Se²⁻ has gained two electrons, its electron configuration is [Ar] 4s²3d¹⁰4p⁶. (d) Ni²⁺: The neutral Ni atom's electron configuration is [Ar] 4s²3d⁸. If Ni²⁺ has lost two electrons, its electron configuration is [Ar] 3d⁶. (e) Br⁻: The neutral Br atom's electron configuration is [Ar] 4s²3d¹⁰4p⁵. Since Br⁻ has gained one electron, its electron configuration is [Ar] 4s²3d¹⁰4p⁶. (f) Mn³⁺: The neutral Mn atom's electron configuration is [Ar] 4s²3d⁵. If Mn³⁺ has lost three electrons, its electron configuration is [Ar] 3d⁴.

Determine which ions possess noble-gas configurations

Now, to identify which ones have the noble-gas configurations, we need to recall those configurations: He: 1s² Ne: [He] 2s²2p⁶ Ar: [Ne] 3s²3p⁶ Kr: [Ar] 4s²3d¹⁰4p⁶ Xe: [Kr] 5s²4d¹⁰5p⁶ Rn: [Xe] 6s²4f¹⁴5d¹⁰6p⁶ Now, we'll compare our ions' electron configurations to the noble gasses': (a) Sr²⁺: [Kr] => noble-gas configuration (Kr) (c) Se²⁻: [Ar] 4s²3d¹⁰4p⁶ => noble-gas configuration (Kr) (e) Br⁻: [Ar] 4s²3d¹⁰4p⁶ => noble-gas configuration (Kr) The ions Sr²⁺, Se²⁻ and Br⁻ possess noble-gas configurations. The other ions do not have noble-gas configurations.

Key concepts

Noble Gas Configuration

The noble gas configuration is a shorthand way to write an element's electron configuration by utilizing the electron configuration of the nearest noble gas. Noble gases have completely filled outer electron shells, which makes them extremely stable. This stability is what many atoms strive to achieve through gaining or losing electrons.
Noble gas configurations are helpful because they provide a clear, clean, and efficient way to convey the electron structure of an element. By referencing the noble gas that has the same number of core electrons as the element, we primarily focus on the valence electrons that determine chemical reactivity.

• Common noble gases include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).
• An example of noble gas configuration is for the ion Strontium (Sr²⁺), which is simply written as [Kr]. Here, Krypton serves as the noble gas reference point as Sr²⁺ indicates a removal of two electrons to attain the same electron structure as Kr.

When ions form a noble gas configuration, they do so by having a full outer electron shell, thereby reaching a mirroring level of inertness similar to noble gases. This occurs through the loss or gain of electrons, as discussed in the original solutions. Sr²⁺, Se²⁻, and Br⁻ showcase noble gas configurations in the exercise.

Ions

Ions are atoms or groups of atoms that have gained or lost one or more electrons, resulting in a net electric charge. This process of losing or gaining electrons is driven by the atom's desire to achieve a more stable electron configuration.
There are two main types of ions:

• Cations, which are positively charged as they lose electrons.
• Anions, which are negatively charged as they gain electrons.

In chemistry, examining the formation of ions is crucial, as it helps us understand reactions and bonding.
In the given exercise:

• For Sr²⁺, the neutral strontium atom loses two electrons, forming a cation with a noble gas configuration of [Kr].
• For Ti²⁺, titanium loses two electrons, resulting in the electron configuration [Ar] 3d², which is not a complete noble gas configuration.

When analyzing ions, it's important to consider how many electrons are exchanged and their effect on achieving desired stable configurations.

Periodic Table

The periodic table is an essential tool in understanding elements and their properties. Arranged by increasing atomic number, this table showcases periodic trends and provides key insights into electron configuration.
Each element in the table is placed based on its atomic structure and characteristics. The layout helps predict an element’s electron configuration and its ability to form ions.

• The table is divided into groups (columns) that share similar properties and periods (rows) indicating the number of electron shells.
• Elements in the same group typically have similar valence electron configurations, which result in comparable chemical behaviors.

For example, looking at Se²⁻ and Br⁻, located in the same period, one can easily predict their electron gain thanks to their small difference from the noble gas krypton (Kr). Through the periodic table, one can derive electron configurations and thus their stability with ease. It serves as the backdrop for understanding chemistry and mastering tasks like the original exercise.