Question

Which noble gas has the same electron configuration as each of the ions in the following compounds? a. calcium bromide, \(\mathrm{CaBr}_{2}\) b. aluminum selenide, \(\mathrm{Al}_{2} \mathrm{Se}_{3}\) c. strontium oxide, SrO d. potassium sulfide, \(\mathrm{K}_{2} \mathrm{S}\)

Short answer

a. calcium bromide, CaBr₂: Argon b. aluminum selenide, Al₂Se₃: Aluminum ion - Neon, Selenium ion - Krypton c. strontium oxide, SrO: Strontium ion - Krypton, Oxygen ion - Neon d. potassium sulfide, K₂S: Argon

Step-by-step solution

Identify the ion charges and electron configurations in the compounds.

First, we need to find the charges of the ions in each compound: a. Calcium has a charge of +2 and bromine has a charge of -1. The electron configurations are: \[\mathrm{[Ca^{2+}] = [Ar]} \quad \mathrm{and} \quad \mathrm{[Br^-] = [Ar]}\] b. Aluminum has a charge of +3 while selenium has a charge of -2. The electron configurations are: \[\mathrm{[Al^{3+}] = [Ne]} \quad \mathrm{and} \quad \mathrm{[Se^{2-}] = [Kr]}\] c. Strontium has a charge of +2, and oxygen has a charge of -2. The electron configurations are: \[\mathrm{[Sr^{2+}] = [Kr]} \quad \mathrm{and} \quad \mathrm{[O^{2-}] = [Ne]}\] d. Potassium has a charge of +1, and sulfur has a charge of -2. The electron configurations are: \[\mathrm{[K^{+}] = [Ar]} \quad \mathrm{and} \quad \mathrm{[S^{2-}] = [Ar]}\]

Match the electron configurations to the noble gases.

Now we can match the electron configurations of the ions to the corresponding noble gases: a. Both calcium and bromine ions have the same electron configuration as Argon. b. The aluminum ion has the same electron configuration as Neon, while the selenium ion matches with Krypton. c. The strontium ion has the same electron configuration as Krypton, and the oxygen ion matches with Neon. d. Both potassium and sulfur ions have the same electron configuration as Argon. Based on these comparisons, the noble gases with the same electron configurations as the ions in the compounds are: a. calcium bromide, CaBr₂: Argon b. aluminum selenide, Al₂Se₃: Aluminum ion - Neon, Selenium ion - Krypton c. strontium oxide, SrO: Strontium ion - Krypton, Oxygen ion - Neon d. potassium sulfide, K₂S: Argon

Key concepts

Noble Gases

Noble gases are unique elements located in Group 18 of the periodic table. They are known for their stability due to having full valence electron shells. This complete outer shell renders them chemically inert, meaning they typically do not form bonds with other elements.
Noble gases include helium, neon, argon, krypton, xenon, and radon. Each of these gases has a specific electron configuration that contributes to its unique properties.

• Helium: \([He] = 1s^2\)
• Neon: \([Ne] = 1s^2 2s^2 2p^6\)
• Argon: \([Ar] = 1s^2 2s^2 2p^6 3s^2 3p^6\)
• Krypton: \([Kr] = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\)
• Xenon: \([Xe] = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\)

Understanding the electron configurations of noble gases is crucial for comparing them to ions formed by other elements.

Ions

An ion is an atom or molecule that has lost or gained one or more electrons, giving it a positive or negative charge. When an atom loses electrons, it becomes a positively charged ion, or cation. Conversely, when it gains electrons, it becomes a negatively charged ion, or anion.
The charge of an ion is determined based on the number of electrons lost or gained and is essential in predicting the behavior of the ion in chemical reactions. Here are a few examples:

• Calcium ion \([Ca^{2+}]\) loses two electrons, resulting in the same electron configuration as argon.
• Bromine ion \([Br^-]\) gains one electron, achieving the argon electron configuration.
• Aluminum ion \([Al^{3+}]\) loses three electrons, equaling the neon configuration.

Knowing how to calculate ion charges helps us understand their electron configurations and compare them to the stable noble gases.

Chemical Compounds

Chemical compounds form when two or more elements chemically bond together. These compounds are characterized by a specific ratio and structure, where the elements involved share or transfer electrons to attain stability.
In the case of ionic compounds, metals usually lose electrons to form positive ions, while non-metals gain these electrons to form negative ions. This electron transfer leads to the formation of electrostatic attractions that hold the compound together. Examples of ionic compounds are calcium bromide and potassium sulfide.
Understanding the formation of these compounds can help us identify electron configurations that mimic noble gases.

Calcium Bromide

Calcium bromide \((CaBr_2)\) is an ionic compound composed of calcium and bromine ions. Calcium, a metal from Group 2, loses two electrons to form a \([Ca^{2+}]\) ion with a configuration like argon.
Bromine, a non-metal, gains one electron per atom to become \([Br^-]\) with a configuration also resembling argon.
In \((CaBr_2)\), one calcium ion pairs with two bromide ions. Upon losing or gaining electrons, the ions achieve full outer shells matching noble gas configurations, Argon in this case, leading to stability in the compound.

Aluminum Selenide

Aluminum selenide \((Al_2Se_3)\) is composed of aluminum and selenium ions. Aluminum, from Group 13, loses three electrons to become \([Al^{3+}]\), adopting a neon-like electron arrangement.
Selenium, across the periodic table in Group 16, gains two electrons to become \([Se^{2-}]\), replicating the electron configuration of krypton.
In \((Al_2Se_3)\), two aluminum ions combine with three selenide ions. This exchange of electrons allows the elements to achieve electron configurations that are similar to stable noble gases, thereby forming a stable compound.

Strontium Oxide

Strontium oxide \((SrO)\) is an ionic compound composed of strontium and oxygen ions. Strontium is a Group 2 metal that loses two electrons to form a \([Sr^{2+}]\) ion, achieving an electron configuration like krypton.
Oxygen, a non-metal from Group 16, gains two electrons to become \([O^{2-}]\), matching the neon configuration.
In \((SrO)\), each strontium ion is paired with an oxide ion to form a stable structure. The electron exchange results in both ions mimicking the configurations of noble gases, which provides stability to the compound.

Potassium Sulfide

Potassium sulfide \((K_2S)\) consists of potassium and sulfur ions. Potassium, from Group 1, loses one electron to become a \([K^+]\) ion with the electron configuration of argon.
Sulfur, a Group 16 element, gains two electrons to form \([S^{2-}]\), also mirroring the argon configuration.

• Each \(K^+\) ion pairs with half of the electron gain of \(S^{2-}\), explaining the \((K_2S)\) stoichiometry.

Both ions aim for a noble gas-like stability, allowing potassium sulfide to stabilize due to its mimetic electron configurations.