Question

Describe the contributions made by the following scientists to the development of the periodic table: a. Stanislao Cannizzaro b. Dmitri Mendeleev c. Henry Moseley

Short answer

Cannizzaro refined atomic weights, Mendeleev organized elements by weight and predicted new ones, and Moseley reordered elements by atomic number.

Step-by-step solution

Introduction to the Contributions

To understand the development of the periodic table, it's essential to know the contributions made by key scientists: Stanislao Cannizzaro, Dmitri Mendeleev, and Henry Moseley.

- Stanislao Cannizzaro

Stanislao Cannizzaro made significant contributions by establishing more accurate atomic weights through his interpretation of Avogadro's hypothesis. He clarified the distinction between atoms and molecules and brought consistency to atomic weight assignments.

- Dmitri Mendeleev

Dmitri Mendeleev is often credited with creating the first widely recognized periodic table. He organized elements by increasing atomic weight and identified periodic trends. He also predicted the existence and properties of elements that had not yet been discovered, which were later confirmed.

- Henry Moseley

Henry Moseley refined the periodic table by arranging elements according to their atomic number rather than atomic weight. Moseley's work established the modern definition of atomic number and resolved discrepancies in Mendeleev's arrangement.

Key concepts

Stanislao Cannizzaro contributions

Stanislao Cannizzaro played a crucial role in the development of the periodic table through his work on atomic weights. Before Cannizzaro, there was a lot of confusion about the correct atomic weights of elements.
Cannizzaro utilized Avogadro's hypothesis, which states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. This allowed him to distinguish between atoms and molecules more accurately.
His efforts resulted in more consistent and accurate atomic weight assignments. By doing so, Cannizzaro laid a solid foundation for the later arrangement of the periodic table.
His work also made it easier to recognize relationships between different elements.
Thanks to Cannizzaro, scientists could start classifying elements based on more accurate data.

Dmitri Mendeleev periodic table

Dmitri Mendeleev is often hailed as the father of the periodic table. Mendeleev's periodic table was groundbreaking because he organized elements by increasing atomic weight and discovered periodic trends.
He noticed that elements with similar properties appeared at regular intervals, or periods.
One of the most impressive aspects of Mendeleev's work was his ability to predict the existence and properties of elements that had not yet been discovered.
This showed that his periodic table was not only a way to classify elements but also a tool for scientific discovery.
For instance, he left gaps in his table where he predicted new elements would fit. These elements were later discovered and found to match his predictions quite well, confirming the validity of his arrangement.

Henry Moseley atomic number

Henry Moseley's contributions were vital to the modern understanding of the periodic table. Moseley discovered that the properties of elements are better correlated with their atomic number, not atomic weight.
He used X-ray spectroscopy to study the elements and found a systematic relationship between X-ray frequencies and atomic number, which is the number of protons in the nucleus of an atom.
This discovery led him to rearrange the periodic table according to atomic number instead of atomic weight.
This resolved inconsistencies in Mendeleev's arrangement and established the modern definition of the atomic number.
Thanks to Moseley, we now understand that the atomic number determines an element's properties and its place in the periodic table. His work also paved the way for the discovery of new elements by predicting their atomic numbers.