Question

The lanthanides, once called the rare earth elements, are really only "medium rare." Using noble gas and spdf notations, depict reasonable electron configurations for the following elements. (a) Samarium, Sm. This lanthanide is used in magnetic materials. (b) Ytterbium, Yb. This element was named for the village of Ytterby in Sweden, where a mineral source of the element was found.

Short answer

(a) Sm: \([\text{Xe}]\ 6s^2\ 4f^6\). (b) Yb: \([\text{Xe}]\ 6s^2\ 4f^{14}\).

Step-by-step solution

Understanding Electron Configuration Notation

Electron configurations describe the distribution of electrons in the atomic orbitals of an atom. The noble gas configuration simplifies this by using the symbol of the previous noble gas to represent the core electrons, followed by the valence electrons depicted in spdf notation.

Identify the Noble Gas Core for Samarium (Sm)

Samarium has the atomic number 62. The noble gas preceding Sm in the periodic table is Xenon (Xe), which has an atomic number of 54. Thus, the noble gas core for Sm is: \[ \text{[Xe]} \]

Determine the Valence Electron Configuration for Samarium (Sm)

After Xenon, the electrons will fill the 6s, 4f, and 5d orbitals. Sm has 8 more electrons than Xe. The configuration for these electrons is: 6s² followed by 4f⁶. Thus, the electron configuration for Sm is: \[ \text{[Xe]}\ 6s^2\ 4f^6 \]

Identify the Noble Gas Core for Ytterbium (Yb)

Ytterbium has the atomic number 70. Like Sm, the noble gas preceding Yb is also Xenon (Xe) with 54 electrons. Thus, Yb's noble gas core is: \[ \text{[Xe]} \]

Determine the Valence Electron Configuration for Ytterbium (Yb)

After Xenon, Yb has 16 additional electrons to distribute among the 6s, 4f, and 5d orbitals. For Yb, these electrons fill as 6s² 4f¹⁴. Thus, Yb's complete electron configuration is: \[ \text{[Xe]}\ 6s^2\ 4f^{14} \]

Key concepts

Lanthanides

The lanthanides are a fascinating group of elements, often considered as "medium rare" rather than truly rare. These elements, including Samarium (Sm) and Ytterbium (Yb), are part of the f-block on the periodic table, which lies in the sixth period. They are characterized by their partially filled 4f orbitals. This unique electronic structure gives rise to many of their complex physical and chemical properties.

Lanthanides are typically known for their magnetic, catalytic, and optical properties. For example, Samarium is widely used in crafting powerful permanent magnets. Ytterbium, named after a Swedish village, plays an important role in various technological applications, including lasers and nuclear medicine. As the 4f orbital fills across the series, these elements exhibit characteristic oxidation states, often showing a +3 state.

• Lanthanides have atomic numbers ranging from 57 (Lanthanum) to 71 (Lutetium).
• The configuration of the 4f orbital highly influences their electronic and chemical behavior.
• Their oxides were once thought to be rare, giving them the name "rare earth elements."

Noble Gas Notation

The noble gas notation is a shorthand method of writing electron configurations that makes understanding and memorizing them easier. It utilizes the concept of core and valence electrons. Instead of writing out the full electron configuration, which can be lengthy, the noble gas that precedes the element of interest in the periodic table is used as a starting reference.

Noble gas notation simplifies electron configurations, focusing on valence electrons, which are primarily responsible for an element's chemical behavior. For elements like Samarium and Ytterbium, the nearest noble gas is Xenon (\(\text{[Xe]}\)), which accounts for the inner electron shells. This means the notation begins with [Xe], followed by the configuration of electrons beyond this core.

• "[Xe] 6s² 4f⁶" for Samarium symbolizes Xenon's complete configuration plus extra electrons.
• Noble gas notation reduces repetition by compactly representing core electrons, emphasizing outer shell electrons.
• This method helps highlight changes between similar elements, such as within the lanthanide series.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. They are crucial in determining how an element will react chemically. Because they are the ones that interact during chemical bonds, understanding their configuration can predict reactivity and bonding patterns.

In the case of the lanthanides like Samarium and Ytterbium, their valence electrons include those in the 6s and 4f subshells. In chemical reactions, these electrons can participate in bonding or be involved in changes in oxidation states.

• For Samarium: \(6s^2 4f^6\), the electrons beyond the Xenon core are considered valence electrons.
• For Ytterbium: \(6s^2 4f^{14}\) illustrates how filling a larger 4f shell impacts its atomic properties. Ytterbium's filled 4f orbital gives it unique stability.
• Valence electrons guide the formation of both ionic and covalent bonds, hence shaping the element's chemical identity.

These electrons, especially the f-block electrons, influence complex phenomena such as magnetism and fluorescence in lanthanides, making them essential in many advanced applications.