Question

Identify the element whose ions have the following electron configurations: (a) a \(2+\) ion with \([\operatorname{Ar}] 3 d^{9}\), (b) a \(1+\) ion with \([\mathrm{Xe}] 4 f^{14} 5 d^{10} 6 \mathrm{~s}^{2}\). How many unpaired electrons does each ion contain?

Short answer

The elements are (a) Copper (Cu) with 1 unpaired electron in the 2+ ion, and (b) Thallium (Tl) with no unpaired electrons in the 1+ ion.

Step-by-step solution

(a) Identify the neutral atom's electron configuration and element for the 2+ ion)

To identify the element whose 2+ ion has the electron configuration [Ar]3d^9, we first need to figure out the electron configuration of the neutral atom. Since the ion has lost 2 electrons, the neutral atom will have 2 more electrons than the ion. The electron configuration of the 2+ ion is [Ar]3d^9, which means it has 18 (from the Argon core) + 9 (from the 3d orbitals) = 27 electrons. Therefore, the neutral atom has 27 + 2 = 29 electrons. Using the periodic table, we can determine that the element with 29 electrons is Copper (Cu), so the electron configuration for the neutral atom is [Ar]3d^10 4s^1.

(a) Calculate the number of unpaired electrons for the 2+ ion)

To find the number of unpaired electrons in the 2+ ion, we need to fill the electron orbitals according to the Aufbau principle and Hund's rule. For [Ar]3d^9 configuration, all 5 d orbitals will have 1 electron each, and 4 of the d orbitals will have an additional electron, which leads to 1 unpaired electron.

(b) Identify the neutral atom's electron configuration and element for the 1+ ion)

To identify the element whose 1+ ion has the electron configuration [Xe]4f^14 5d^10 6s^2, we first need to figure out the electron configuration of the neutral atom. Since the ion has lost 1 electron, the neutral atom will have 1 more electron than the ion. The electron configuration of the 1+ ion is [Xe]4f^14 5d^10 6s^2, which means it has 54 (from the Xenon core) + 14 (from the 4f orbitals) + 10 (from the 5d orbitals) + 2 (from the 6s orbitals) = 80 electrons. Therefore, the neutral atom has 80 + 1 = 81 electrons. Using the periodic table, we can determine that the element with 81 electrons is Thallium (Tl), so the electron configuration for the neutral atom is [Xe]4f^14 5d^10 6s^2 6p^1.

(b) Calculate the number of unpaired electrons for the 1+ ion)

In the 1+ ion with the electron configuration of [Xe]4f^14 5d^10 6s^2, all the orbitals are fully occupied, so there are no unpaired electrons. In conclusion, the elements are Copper (Cu) for (a) and Thallium (Tl) for (b), and the number of unpaired electrons in the ions are 1 and 0, respectively.

Key concepts

Unpaired Electrons

Unpaired electrons are electrons that occupy an orbital alone rather than in pairs. They play a significant role in the magnetic properties of an atom or ion. In electron configurations, unpaired electrons are usually found in partially filled orbitals.

Unpaired electrons can be identified using Hund’s Rule, which states that electrons will fill each orbital in a subshell singly before any orbital gets a second electron. This means unpaired electrons are always the last to be added in a partially filled shell.

• For the configuration [Ar]3d⁹, four d orbitals are fully paired, and one is unpaired.
• For [Xe]4f¹⁴5d¹⁰6s², there are no unpaired electrons as all orbitals are fully filled.

Copper

Copper is an essential transition metal with atomic number 29. It is well known for its unique electron configuration, which can be surprising due to electron-electron interactions.

• The unusual configuration [Ar]3d¹⁰4s¹ arises because what's energetically favorable differs from what the Aufbau principle might predict.
• Copper commonly forms a 2+ ion, moving to [Ar]3d⁹ and resulting in one unpaired electron.

Copper's electron distribution is particularly important in electrical conductivity and its unique chemical properties.

Thallium

Thallium is another interesting element with atomic number 81. It belongs to the post-transition metals in the periodic table and behaves somewhat differently than transition metals like copper.

• The neutral atom configuration is [Xe]4f¹⁴5d¹⁰6s²6p¹, mimicking the hesitation before filling the p orbital.
• Thallium tends to form a 1+ ion, resulting in [Xe]4f¹⁴5d¹⁰6s², with fully filled orbitals and no unpaired electrons.

Thallium's chemical behavior, specifically the choice between a 1+ and 3+ state, is influenced by the stability of these configurations.

Electron Orbitals

Electron orbitals are regions around the nucleus where electrons are likely found. They are vital in defining an element’s chemical properties and interactions.

• Orbitals come in different shapes and designs: s, p, d, and f, each with specific numbers and configurations.
• The s orbitals hold a maximum of 2 electrons, p hold 6, d hold 10, and f hold 14.

Understanding electron orbitals helps us determine the electronic structure and stability of ions and atoms like copper and thallium. Skills in reading and interpreting these configurations are crucial for mastering chemistry concepts.