Problem 2 - Chemistry and Chemical Reactivity

Question

Identify, based on the position in the periodic table, the actinide elements among those in the following list: Ta, Tc, Ti, Th, Tm.

Step-by-Step Solution

Answer

The actinide element in the list is Thorium (Th).

Step 1: Understand Actinide Elements

The actinide series consists of 15 elements from actinium (Ac) to lawrencium (Lr) in the periodic table, with atomic numbers 89 to 103. These elements are present in the f-block of the periodic table.

Step 2: Locate Each Element in the Periodic Table

- **Ta (Tantalum)**: Atomic number 73, located in the d-block, not an actinide. - **Tc (Technetium)**: Atomic number 43, located in the d-block, not an actinide. - **Ti (Titanium)**: Atomic number 22, located in the d-block, not an actinide. - **Th (Thorium)**: Atomic number 90, located in the f-block, is an actinide. - **Tm (Thulium)**: Atomic number 69, located in the f-block, but it is not an actinide (it is a lanthanide).

Step 3: Identify the Actinide Element

The only element from the given list that is part of the actinide series is Thorium (Th), with atomic number 90.

Key Concepts

Periodic Table

The Periodic Table is a structured arrangement of all known chemical elements in order based on their atomic number, electron configuration, and recurring chemical properties. It serves as a fundamental tool in chemistry for understanding properties and relationships among elements.

• Each element on the table is assigned a unique position determined by its atomic number, which is the number of protons in the nucleus of an atom.
• The table is organized in rows called periods and columns known as groups.

Elements in the same group often share similar chemical behaviors. The f-block elements, which include the lanthanides and actinides, are positioned at the bottom of the table to maintain its grid-like organization.

f-block Elements

The f-block elements, also known as inner transition metals, are found in the two rows beneath the main body of the periodic table. They are typically divided into two series: lanthanides and actinides.

• Lanthanides range from lanthanum (La) to lutetium (Lu) and are located in the 4f sublevel.
• Actinides stretch from actinium (Ac) to lawrencium (Lr), occupying the 5f sublevel.

These elements are typically characterized by their ability to exhibit multiple oxidation states, which is largely due to their f-electrons. Often, they are associated with complex chemistry and high atomic weights. Actinides are particularly notable for their radioactivity, with many having no stable isotopes.

Atomic Numbers

The atomic number is a fundamental characteristic of an element, reflecting the total number of protons present in its atomic nucleus. This number is unique for each element and determines its position on the periodic table.

• The atomic number not only identifies the element but also provides insight into its electron distribution, which influences the element's chemical properties and behavior.
• For example, thorium (Th), with an atomic number of 90, is an actinide. The high atomic numbers in this series lead to large, complex nuclei that contribute to the unique radioactive properties of actinides.

Understanding atomic numbers is crucial for comprehending how elements are grouped in the periodic table and why certain elements behave similarly or differently compared to others.