The fourteen elements (atomic number 90-103) after actinium are called?

1. Analyze the question

The question asks for the specific name given to the series of 14 chemical elements that follow Actinium (atomic number 89) in the periodic table, specifically those with atomic numbers 90 through 103.

2. Explain the concept

In the periodic table, there are two rows of elements usually placed at the bottom to prevent the table from becoming too wide.

• The first row (atomic numbers 57–71) follows Lanthanum and is called the Lanthanoids (or Lanthanides).
• The second row (atomic numbers 89–103) follows Actinium. These elements are known as the Actinoids (or Actinides).

These elements are characterized by the filling of the 5f electron subshell. Because they all share similar chemical properties to Actinium, they are grouped together in this series.

3. Show the solution

• Step 1: Identify the position of Actinium in the periodic table. Actinium has an atomic number of 89.
• Step 2: Identify the elements that follow it. The elements from atomic number 90 (Thorium) to 103 (Lawrencium) are placed in the f-block of the periodic table.
• Step 3: Apply the nomenclature rule. Just as elements following Lanthanum are called Lanthanoids, elements following Actinium are named Actinoids.
• Step 4: Evaluate the options. • A. Actinoids: This matches the standard chemical nomenclature for this series. • B. Nucleotides: These are biological molecules (the building blocks of DNA/RNA), not chemical elements. • C. Pre-actinum elements: This is incorrect as these elements come after Actinium, not before. • D. Atomic elements: This is a generic term that applies to all elements, not a specific group name.

4. Identify the answer

The correct term for the series of elements from atomic number 90 to 103 is Actinoids.

5. Exam Tip

To remember this easily, think of the "f-block" elements as the "bottom-block" elements. Remember: Lanthanoids start with Lanthanum (Atomic number 57), and Actinoids start with Actinium (Atomic number 89).