Dmitri Mendeleev, a pioneering Russian chemist, developed one of the earliest successful versions of the periodic table. His arrangement was a significant step in organizing the known chemical elements.

Mendeleev's Arrangement Strategy

Mendeleev's primary method for arranging the elements was based on two key principles:

• Increasing Atomic Mass: He initially arranged the elements in order of increasing atomic mass.
• Grouping Similar Properties: Crucially, he prioritized grouping elements with similar chemical and physical properties together. When the order of atomic mass would separate elements with similar properties, he adjusted the sequence.

Grouping Elements with Similar Properties

To group elements with similar properties, Mendeleev arranged them in vertical columns, which are known today as groups. Elements within the same vertical column share similar characteristics and exhibit similar chemical behaviors. For example, the alkali metals (like Lithium, Sodium, Potassium) are all found in the same group because they share properties such as high reactivity and forming positive ions with a +1 charge.

Analyzing the Options

Let's look at why the other options are less accurate descriptions of Mendeleev's method for grouping similar properties:

• Horizontal row: Horizontal rows are known as periods. While elements are placed in order of increasing atomic mass across a period, elements in the same row do not necessarily share the same properties.
• Atomic series: This term is not standard terminology for describing the arrangement of elements in Mendeleev's periodic table.
• Block: In the modern periodic table, elements are categorized into blocks (s, p, d, f) based on the orbital their valence electrons occupy. This classification wasn't a primary organizing principle for Mendeleev.

Therefore, Mendeleev arranged elements with similar properties in vertical columns (groups) of his periodic table.