Examine Figure 2.2, A portion of Mendeleev's periodic table. (a) Which characteristic was used to organize the elements in the table?

Key Concepts

Periodic Law

The Periodic Law states that the properties of elements are a periodic function of their atomic numbers. Mendeleev organized his periodic table based on this principle, arranging elements in order of increasing atomic mass while grouping them by similar chemical properties. This organization allowed for the prediction of undiscovered elements and their properties.

Atomic Mass

Atomic mass is the weighted average mass of an element's isotopes, measured in atomic mass units (amu). Mendeleev initially used atomic mass as the primary criterion for arranging elements in his periodic table. This approach highlighted the relationship between an element's mass and its chemical behavior, although modern periodic tables are organized by atomic number.

Group and Period

In the context of the periodic table, a group refers to a vertical column of elements that share similar chemical properties, while a period refers to a horizontal row. Mendeleev's table grouped elements with analogous characteristics, allowing for easier identification of trends and relationships among elements. This structural organization is fundamental to understanding the behavior of elements in chemical reactions.