Question

In which period and group does an electron first appear in an \(f\) orbital?

Short answer

An electron first appears in an f orbital in period 6, but the f-block elements are not assigned to a traditional group.

Step-by-step solution

Identifying the Period for the First Appearance of an Electron in an f Orbital

The first time an electron appears in an f orbital is for the element cerium (Ce), which has the atomic number 58. This takes place in the lanthanide series, starting with the element lanthanum (La), atomic number 57. The lanthanide series is a part of period 6 of the periodic table.

Determining the Group for the f Orbital Appearance

The lanthanides, where f orbitals start to fill, are not assigned to a specific group. They are placed below the main body of the periodic table in a separate block, often referred to as the f-block. Hence, they do not belong to any of the traditional groups (1-18).

Key concepts

Electron Configuration

Understanding electron configuration is crucial in the world of chemistry and quantum mechanics. It details how electrons are distributed in orbitals, subshells, and shells around an atom's nucleus. Electrons are arranged in energy levels or shells, each with subshells labeled as s, p, d, and f. The f subshell, which is our focus, has seven orbitals, each capable of holding two electrons, for a total of up to 14 electrons.

When addressing electron configurations, it is important, to begin with the lowest energy level, filling each subshell according to the Aufbau principle. Hund's rule and the Pauli exclusion principle also play a role in determining how electrons fill these orbitals. Understanding this fundamental concept allows students to predict an element's chemical properties and place it correctly within the framework of the periodic table.

Lanthanide Series

The lanthanide series contains a set of 15 metallic elements, from lanthanum (La) to lutetium (Lu), occupying atomic numbers 57 through 71. These elements, often called lanthanoids or rare earth elements, are noteworthy for their similar properties, including their reactivity and the way they exhibit 'lanthanide contraction'.

This series marks the introduction of f orbitals in the electron configurations of elements. They have significant importance in various industries, ranging from electronics to energy solutions. A common characteristic of the lanthanide series is that the 4f orbitals are being populated with electrons as we progress through the series.

Periodic Table Periods

The periodic table is organized into rows known as periods that run from left to right. These periods are crucial in understanding the organization of the elements and their properties. For instance, all elements in a given period have the same number of atomic orbitals. In relation to the exercise, we focus on period 6, which is the first period where f orbitals start to get filled, specifically starting with the element cerium (Ce).

This period includes a mix of very diverse elements, ranging from transition metals to the inner transition metals of the lanthanide series. Periods in the periodic table help categorize elements into groups with similar chemical behavior due to their shared electron configurations.

Atomic Number

The atomic number of an element is a fundamental property that represents the number of protons found in the nucleus of an atom. It is denoted with the symbol Z and uniquely identifies each element. The atomic number determines the position of an element in the periodic table since the elements are ordered by increasing atomic number.

In the context of our exercise, the atomic number is pivotal when we look at the f orbitals first beginning to occupy electrons. With cerium, the atomic number is 58, and it signals the onset of electron occupation in f orbitals within the lanthanide series. Understanding atomic numbers allows students to navigate the periodic table and comprehend the patterns in electron configuration among elements.