Examine Figure 2.2, A portion of Mendeleev's periodic table. How was Mendeleev able to predict with a high level of accuracy the properties of the undiscovered elements beneath Al and Si in the periodic table?

Verified step by step guidance

1. Identify the pattern in the properties of elements: Mendeleev observed that elements when arranged in order of increasing atomic mass showed a periodic pattern in their properties. This pattern repeated itself, which helped him predict the properties of unknown elements.
2. Use the properties of neighboring elements: Mendeleev looked at the properties of elements surrounding the gaps in his periodic table. By analyzing the trends in these properties (like atomic mass, density, melting point, etc.), he could infer the properties of the undiscovered elements.
3. Interpolate the properties: Mendeleev used interpolation, a method of estimating unknown values by using the known values on either side of the gap. This allowed him to estimate the atomic mass and other properties of the missing elements.
4. Position in the periodic table: The position of an element in Mendeleev's table (which was organized by both atomic mass and chemical properties) was crucial. Elements in the same group (vertical columns) typically have similar chemical properties, which helped in predicting the properties of new elements.
5. Refine predictions with chemical behavior: Mendeleev also considered how elements reacted chemically with other elements. By understanding the chemical behavior of known elements in the same group or period, he could predict how the undiscovered elements would react.

Key Concepts

Periodic Law

Mendeleev's periodic law states that the properties of elements are a periodic function of their atomic weights. This means that when elements are arranged in order of increasing atomic weight, elements with similar properties appear at regular intervals. This foundational principle allowed Mendeleev to organize the periodic table and predict the properties of undiscovered elements based on their position.

Element Properties and Trends

Elements in the periodic table exhibit trends in properties such as electronegativity, atomic radius, and ionization energy. Mendeleev recognized these trends and used them to infer the characteristics of elements that had not yet been discovered. For example, he could predict that elements below aluminum (Al) and silicon (Si) would share similar chemical behaviors due to their placement in the same group.

Gaps in the Periodic Table

Mendeleev intentionally left gaps in his periodic table for elements that had not yet been discovered, believing that these elements would eventually be found. He predicted their existence and properties based on the patterns he observed in the table. This foresight demonstrated his understanding of the periodic nature of elements and the relationships between them, which later proved to be accurate with the discovery of new elements.