Question

Write the electron configurations for the following ions, and determine which have noble-gas configurations: (a) \(\mathrm{Ti}^{2+},(\mathbf{b})\) (d) \(\mathrm{PO}^{2-}\), (f) \(\mathrm{V}^{3+}\) \(\mathrm{Br}^{-}\) (c) \(\mathrm{Mg}^{2+}\) (e) \(\mathrm{Pt}^{2+}\)

Short answer

The electron configurations for the given ions are: - \(\mathrm{Ti}^{2+}\): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² (no noble-gas configuration) - \(\mathrm{Br}^{-}\): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ (noble-gas configuration) - \(\mathrm{Mg}^{2+}\): 1s² 2s² 2p⁶ (noble-gas configuration) - \(\mathrm{PO}^{2-}\): 1s² 2s² 2p⁶ 3s² 3p⁵ (no noble-gas configuration) - \(\mathrm{Pt}^{2+}\): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁹ (no noble-gas configuration) - \(\mathrm{V}^{3+}\): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² (no noble-gas configuration)

Step-by-step solution

(a) Ti²⁺

The titanium ion has an atomic number of 22, but due to the charge (+2), it loses two electrons. Therefore, Ti²⁺ has 20 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². This matches the electron configuration of calcium (Ca, atomic number 20) and is not a noble-gas configuration, as it is different from the nearest noble gas, Argon (Ar, atomic number 18).

(b) Br⁻

The bromine ion has an atomic number of 35 and gains one electron due to its negative charge. Therefore, Br⁻ has 36 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶. This matches the electron configuration of the noble gas Krypton (Kr, atomic number 36); thus, Br⁻ has a noble-gas configuration.

(c) Mg²⁺

The magnesium ion has an atomic number of 12 and loses two electrons due to the charge (+2). Mg²⁺ has 10 electrons. Its electron configuration is 1s² 2s² 2p⁶. This matches the electron configuration of the noble gas Neon (Ne, atomic number 10); thus, Mg²⁺ has a noble-gas configuration.

(d) PO₂⁻

Phosphorous (P) has an atomic number of 15. However, due to the charge (-2), it gains two electrons. Thus, PO₂⁻ has 17 electrons. The electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁵. This does not match the electron configuration of the nearest noble gas, Argon (Ar, atomic number 18); hence, PO₂⁻ does not have a noble-gas configuration.

(e) Pt²⁺

Platinum (Pt) has an atomic number of 78. Due to its charge (+2), it loses two electrons. Thus, Pt²⁺ has 76 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁹. This does not match the electron configuration of the nearest noble gas, Xenon (Xe, atomic number 54); hence, Pt²⁺ does not have a noble-gas configuration.

(f) V³⁺

Vanadium (V) has an atomic number of 23. Due to its charge(+3), it loses three electrons. Thus, V³⁺ has 20 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². This matches the electron configuration of calcium (Ca, atomic number 20) and is not a noble-gas configuration, as it is different from the nearest noble gas, Argon (Ar, atomic number 18). To summarize: - \(\mathrm{Ti}^{2+}\) does not have a noble-gas configuration - \(\mathrm{Br}^{-}\) has a noble-gas configuration - \(\mathrm{Mg}^{2+}\) has a noble-gas configuration - \(\mathrm{PO}^{2-}\) does not have a noble-gas configuration - \(\mathrm{Pt}^{2+}\) does not have a noble-gas configuration - \(\mathrm{V}^{3+}\) does not have a noble-gas configuration

Key concepts

Noble Gas Configuration

In the world of chemistry, noble gas configuration is a term used to describe the electron arrangement found in the noble gases like helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These elements have the most stable electron configurations, characterized by fully filled outer electron shells.
When ions attain an electron configuration identical to that of a noble gas, they are considered to possess a noble gas configuration. This means the electrons in the ion arrange themselves into completely filled shells, leading to increased stability.
If we consider bromide ion (Br⁻) as an example, it achieves a noble gas configuration by gaining one electron. This additional electron gives it the electronic arrangement of krypton, a noble gas. Similarly, magnesium ion (Mg²⁺) loses two electrons to match the electron distribution of neon, another noble gas.
These ions with noble gas configurations are particularly stable due to their energy-efficient electron arrangements. This stability is why many elements strive to lose or gain electrons to mimic the structure of noble gases.

Ions

An ion is an atom or molecule that has gained or lost one or more electrons, resulting in a net electric charge. This process can yield positive ions called cations, which lose electrons, or negative ions called anions, which gain electrons.
Understanding how ions form helps to predict their behavior in chemical reactions. The number of electrons lost or gained depends on the element and its need to achieve a more stable electron configuration.
For example, titanium (Ti) typically forms the cation Ti²⁺ by losing two electrons. In this state, it has a total of 20 electrons. On the other hand, phosphorous forms the anion PO²⁻ by gaining two electrons, going from 15 to 17 electrons in total.
Whether they are gaining or losing electrons, the overall goal for ions is to reach a stable state. This often seen in their tendency to match the electron configurations of the noble gases, which are known for their chemical inertness and associated stability.

Electron Loss and Gain

The process of electron loss and gain is fundamental to the formation of ions in chemistry. An atom achieves or loses electrons to stabilize its electron shell configurations.
During electron loss, atoms shed electrons, often from their outer shell, becoming cations. This occurs when metals like magnesium (Mg) and vanadium (V) form cations such as Mg²⁺ and V³⁺, respectively. These ions lose electrons to downgrade into a more stable state, preferably reaching an electron configuration like a noble gas.
Conversely, electron gain is seen when atoms accept additional electrons, resulting in anions. A non-metal like bromine (Br) will gain an electron to become Br⁻. This addition shifts its electron count to mimic the adeptly full configuration of the nearest noble gas.
In essence, the drive to achieve more stable configurations, often akin to noble gases, motivates atoms to undergo electron loss or gain. This movement enhances chemical stability, guiding the reactivity and interactions of different elements.