Which lanthanide has the maximum number of unpaired electrons in both its atom and its \(3+\) ion? Give the number of unpaired electrons in the atom and in the ion.

The lanthanide series is a group of elements in the periodic table with atomic numbers from 57 to 71. They are sometimes referred to as rare earth elements. Lanthanides are known for their unique properties such as high magnetic susceptibility and intricate electron configurations. These elements have their 4f orbitals progressively filled, which largely determines their chemical and physical behavior.
Lanthanides are usually shiny and silvery-white. They can tarnish when exposed to air. They are also known for their ability to produce bright colors in compounds, which makes them useful for things like screen displays and lighting.
These elements are also essential in many advanced technologies, including medical imaging, magnets, and lasers. Understanding the properties and electron configurations of lanthanides is critical for harnessing their full potential.

Electron configuration refers to the distribution of electrons among the various orbitals of an atom. For lanthanides, this involves filling the 4f, 5d, and 6s orbitals. For example, Cerium (Ce) has an electron configuration of \[ \text{[Xe]} 4f^1 5d^1 6s^2 \].
The configuration of electrons directly influences the chemical properties of an element. Lanthanides, in particular, have complex configurations because of the involvement of 4f orbitals. The number of electrons in these orbitals can influence the magnetic and optical properties of the elements.
Writing out the electron configuration for each lanthanide helps in identifying their chemical behavior. For example, Gadolinium (Gd) has the configuration \[ \text{[Xe]} 4f^7 5d^1 6s^2 \], indicating that it has seven unpaired 4f electrons.

Unpaired electrons are electrons that occupy an orbital alone rather than in a pair with another electron. The number of unpaired electrons in an atom or ion is crucial because it determines the magnetic properties of that species. Elements with more unpaired electrons generally exhibit stronger magnetic properties.
In the context of lanthanides, Gadolinium (Gd) stands out with the maximum number of unpaired electrons. In its ground state, Gadolinium has seven unpaired electrons located in the 4f orbitals. When it forms a \[ \text{Gd}^{3+} \] ion by losing three electrons, it still retains seven unpaired electrons in the 4f orbitals. This makes Gadolinium highly magnetic both in its atomic form and in its \[ \text{Gd}^{3+} \] ion form.
Knowing the number of unpaired electrons can help in various applications, such as developing better magnetic materials or more effective chemical reactions that depend on magnetic properties.