Question

Hund's rule, a component of the Aufbauprinzip (construction principle), states that as one moves across the periodic table, with increasing atomic number, the available subshells are filled successively with one electron in each orbital, their spins all parallel; only when all orbitals in a subshell contain one electron are second electrons, with spins opposite to the first, placed in the orbitals. Explain why the ground-state electron configurations of successive elements should follow this pattern.

Short answer

Question: Explain how the ground-state electron configurations of successive elements follow the pattern described by Hund's rule. Answer: The ground-state electron configurations of successive elements follow Hund's rule by first filling each orbital within a subshell with one electron of the same spin before pairing up with electrons of opposite spins. This configuration ensures that the atom has the lowest possible energy, which is the most stable state. As we move across the periodic table, electrons are added to orbitals following the Pauli Exclusion Principle, Aufbau Principle, and Hund's rule, with a focus on maximizing electron spins and minimizing electron repulsion.

Step-by-step solution

Understand Hund's rule

Hund's rule is a principle used to determine the electronic configuration of atoms in their ground state, as they fill up with electrons in the periodic table. According to this rule, electrons are added to the orbitals in a way that maximizes the total spin of the electrons in a given subshell, before they start pairing up with opposite spins. This ensures that the atom has the lowest possible energy (which is the most stable state).

Explain how orbitals are filled with electrons

As we move across the periodic table and fill electrons into the orbitals, we follow three main rules – the Pauli Exclusion Principle, the Aufbau Principle, and Hund's rule. From the Aufbau Principle, we know that lower energy orbitals are filled before higher energy ones. The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of quantum numbers, meaning each orbital can hold a maximum of two electrons with opposite spins.

Explain the role of electron spins

Hund's rule takes into account the electron spins. When filling electrons into degenerate orbitals (orbitals having the same energy level) within a subshell, one electron is added to each orbital before they start pairing up with opposite spins. Electrons with parallel spins are more stable due to minimized repulsion between them. As a result, an atom reaches its ground-state electron configuration when it has the lowest possible energy, conforming to Hund's rule.

Apply Hund's rule to successive elements

To illustrate the pattern described by Hund's rule, let's consider adding electrons to the p subshell (which has three orbitals). As we move from element to element across the periodic table (with increasing atomic numbers), electrons will be added following Hund's rule, as mentioned: Element 1: 1 electron in the first orbital (spin up) Element 2: 1 electron in the first orbital (spin up) and 1 electron in the second orbital (spin up) Element 3: 1 electron in the first orbital (spin up), 1 electron in the second orbital (spin up), and 1 electron in the third orbital (spin up) Element 4: 1 electron in the first orbital (spin up), 1 electron in the second orbital (spin up), 1 electron in the third orbital (spin up), and the second electron in the first orbital (spin down) Element 5: Similar process is followed for the fifth element adding a second electron in the second orbital (spin down) and so on. This example thus demonstrates how the ground-state electron configurations of successive elements follow the pattern described by Hund's rule.