Question

Which noble gas is isoelectronic with each of the following metal ions? (a) \(\mathrm{Li}^{+}\) (b) \(\mathrm{Al}^{3+}\) (c) \(\mathrm{Ca}^{2+}\) (d) \(\mathrm{Mg}^{2+}\)

Short answer

(a) He, (b) Ne, (c) Ar, (d) Ne

Step-by-step solution

- Understanding Isoelectronic Species

Isoelectronic species are atoms, molecules, or ions that have the same number of electrons. To find the noble gas isoelectronic with a given ion, we need to determine the electron count of the ion and match it with a noble gas.

- Identify Electrons in Neutral Atoms

Start by determining the number of electrons in each neutral atom of the given elements before they form ions. Neutral lithium (Li) has 3 electrons, neutral aluminum (Al) has 13 electrons, neutral calcium (Ca) has 20 electrons, and neutral magnesium (Mg) has 12 electrons.

- Determine Electron Count for Each Ion

Calculate the number of electrons for each ion:(a) \( ext{Li}^+\): One electron is lost from Li, so \(3 - 1 = 2\) electrons.(b) \( ext{Al}^{3+}\): Three electrons are lost from Al, so \(13 - 3 = 10\) electrons.(c) \( ext{Ca}^{2+}\): Two electrons are lost from Ca, so \(20 - 2 = 18\) electrons.(d) \( ext{Mg}^{2+}\): Two electrons are lost from Mg, so \(12 - 2 = 10\) electrons.

- Match Electron Count with Noble Gases

Each ion's electron count is matched to the electron configuration of a noble gas:(a) \( ext{Li}^+\) with 2 electrons matches Helium (He).(b) \( ext{Al}^{3+}\) with 10 electrons matches Neon (Ne).(c) \( ext{Ca}^{2+}\) with 18 electrons matches Argon (Ar).(d) \( ext{Mg}^{2+}\) with 10 electrons matches Neon (Ne).

Key concepts

Noble Gases

Noble gases are a group of elements located in the last column of the periodic table. These elements are known for their complete outer electron shells, which make them highly stable and unreactive in nature. This stability results from having a full set of electrons in their outer shell. Because of this, noble gases rarely form chemical compounds with other elements.In the context of isoelectronic species, noble gases serve as a reference point. Specifically, when a metal ion loses electrons and becomes positively charged, it might end up with the same number of electrons as a noble gas. This creates an isoelectronic relationship. For instance, upon losing an electron, a lithium ion (\(\mathrm{Li}^+\)) will have two electrons, matching the electron count of helium (\(\mathrm{He}\)), the first noble gas. Understanding these properties helps in predicting how ions behave and interact in chemical reactions.

Electron Configuration

Electron configuration refers to the distribution of electrons in the atomic orbitals of an atom. It's crucial because it dictates the chemical properties and reactivity of elements. Electrons fill orbitals beginning with the lowest energy levels, following a specific order known as the Aufbau principle. For instance, the electron configuration of a neutral lithium atom (\(\mathrm{Li}\)) is 1s² 2s¹, with 3 electrons in total.When atoms form ions, they gain or lose electrons, altering their electron configuration. As a result, ions may become isoelectronic with noble gases. For example, a lithium ion (\(\mathrm{Li}^+\)) loses one electron, resulting in a configuration of 1s², the same as helium. Recognizing these changes allows us to predict the behavior of ions in various chemical contexts. This understanding is key in determining how ions will bond and the stability of those new structures.

Metal Ions

Metal ions are atoms of metallic elements that have lost one or more electrons, resulting in positively charged species. Metals tend to lose electrons to achieve a stable electron configuration, often resembling that of noble gases. This electron loss usually leads to a more stable state as it completes an outer electron shell.Consider aluminum (\(\mathrm{Al}\)), which usually loses three electrons to form \(\mathrm{Al}^{3+}\). After losing these electrons, its electron configuration matches that of neon, a noble gas. This tendency to form ions is a characteristic trait of metals, enabling them to participate in various chemical reactions, such as forming ionic compounds with nonmetals.Understanding metal ions and their electron configurations helps explain why metals conduct electricity, their role in catalysis, and their widespread use in various industrial applications. It's a fundamental part of chemistry that reveals how elements achieve chemical stability.