Question

Refer to the periodic table and predict which of the following ions are isoelectronic with the noble gas argon: (a) \(\mathrm{Al}^{3+}\) (b) \(\mathrm{Ca}^{2+}\) (c) \(S^{2-}\) (d) \(\mathrm{N}^{3-}\)

Short answer

Isoelectronic ions with argon are \(\mathrm{Ca}^{2+}\) and \(S^{2-}\).

Step-by-step solution

Determine the Electron Configuration of Argon

Argon is a noble gas with an atomic number of 18, meaning it has 18 electrons. The electron configuration of argon is \([1s^2 2s^2 2p^6 3s^2 3p^6]\), which totals 18 electrons.

Calculate the Electron Count for Each Ion

To determine if an ion is isoelectronic with argon, calculate the number of electrons in each ion:- \(\mathrm{Al}^{3+} \) has lost 3 electrons from the neutral aluminum atom (13 - 3 = 10 electrons).- \(\mathrm{Ca}^{2+} \) loses 2 electrons from the neutral calcium atom (20 - 2 = 18 electrons).- \(S^{2-}\) gains 2 electrons to the neutral sulfur atom (16 + 2 = 18 electrons).- \(\mathrm{N}^{3-}\) gains 3 electrons to the neutral nitrogen atom (7 + 3 = 10 electrons).

Identify Isoelectronic Ions

Compare the electron counts of each ion to argon:- \(\mathrm{Al}^{3+} \) has 10 electrons, not 18, so it is not isoelectronic with argon.- \(\mathrm{Ca}^{2+}\) has 18 electrons, matching argon.- \(S^{2-}\) has 18 electrons, matching argon.- \(\mathrm{N}^{3-}\) has 10 electrons, not 18, so it is not isoelectronic with argon.

Conclusion

The ions that are isoelectronic with argon and have the same number of electrons (18) are \(\mathrm{Ca}^{2+}\) and \(S^{2-}\).

Key concepts

Electron Configuration

Electron configuration refers to the arrangement of electrons in the orbitals of an atom. Electrons are distributed among different energy levels or shells, and within those shells, they are further arranged in subshells. These arrangements are dictated by the principles of quantum mechanics. The configuration is often written in a notation that illustrates these arrangements, showing how electrons are positioned in order from lower to higher energy orbitals. For example, the electron configuration of the noble gas argon is written as \[1s^2 2s^2 2p^6 3s^2 3p^6\] which indicates two electrons in the 1s orbital, two in the 2s, six in the 2p, two in the 3s, and finally, six in the 3p orbitals, totaling 18 electrons overall.

Noble Gases

Noble gases are a group of chemical elements that are typically unreactive and stable. They are found in Group 18 of the Periodic Table and include elements like helium, neon, argon, krypton, xenon, and radon. What makes noble gases unique is their full valence shell of electrons. This means that they have a complete complement of electrons in their outermost energy level, which makes them chemically inert under most conditions. Argon, for example, has a full valence shell configuration of \[3s^2 3p^6\]This stable configuration gives noble gases their characteristic lack of reactivity, as they have no tendency to gain or lose electrons.

Periodic Table

The Periodic Table is an organized chart of elements arranged by increasing atomic number. It is structured so that elements with similar properties fall into the same columns, known as groups. These similarities in behavior arise because elements in the same group have the same number of electrons in their outermost shell, known as valence electrons. The table helps predict properties of elements and how they interact with each other.

• Group 18: Contains noble gases, known for full valence shells.
• Group 1: Alkali metals, highly reactive due to one valence electron.
• Group 17: Halogens, reactive nonmetals, eager to gain an electron.

The location of an element in the Periodic Table can give insights into its chemical behavior and potential for forming isoelectronic ions.

Electron Count

Electron count in ions is crucial for determining their electronic configuration and chemical properties. When atoms form ions, they either lose or gain electrons to attain a more stable electronic state, often acquiring a configuration similar to the nearest noble gas.

• Positively charged ions (cations) occur when atoms lose electrons. For example, \(\text{Al}^{3+}\) is formed when aluminum loses three electrons.
• Negatively charged ions (anions) form when atoms gain electrons. \(\text{S}^{2-}\) is created when sulfur gains two additional electrons.

To determine if an ion is isoelectronic with a noble gas like argon, calculate the total number of electrons after electron gain or loss and compare it to the noble gas, which has a specific electron count. Isoelectronic ions share the same number of electrons, leading to similar electron configurations.