Question

Why did Mendeleev not include krypton in his periodic table of \(1871 ?\)

Short answer

Mendeleev didn't include krypton because it wasn't discovered until 1898, after his 1871 table.

Step-by-step solution

Understanding the Historical Context

Mendeleev published his periodic table in 1869, and he was working to organize elements known at that time based on atomic masses and chemical properties. His table allowed for the prediction of undiscovered elements.

Identifying Known Elements at the Time

In 1871, krypton had not yet been discovered. The only elements Mendeleev could include in his periodic table were those known to scientists at the time.

Discovery of Krypton

Krypton was discovered in 1898 by Sir William Ramsay and Morris Travers, well after Mendeleev's periodic table of 1871. Ramsay and Travers isolated krypton while studying residue from evaporated air.

Mendeleev's Recognition of Gaps

Mendeleev's table was notable for its ability to predict elements that fit into gaps he left, based on the periodicity and trends of known elements. However, without knowledge of krypton, he couldn't account for noble gases.

Key concepts

discovery of krypton

The discovery of krypton is a fascinating story in the history of chemistry. Krypton was discovered in 1898 by two notable scientists: Sir William Ramsay and Morris Travers. Their work was groundbreaking because they isolated krypton while studying the residue from evaporated air. This discovery was an essential milestone as it added to the group of elements known as the noble gases.

Ramsay and Travers were not initially looking for krypton specifically. They were investigating the components of liquefied air and stumbled upon krypton as a byproduct during their experiments. This element was characterized by a unique bright-line spectrum, which helped in identifying it.

• Ramsay's earlier work on gases, including the discovery of argon, set the stage for uncovering krypton.
• Krypton's discovery contributed to the broader understanding of atmospheric gases and their applications.

Today, krypton is used in various applications, including lighting and lasers, due to its unique properties.

noble gases

Noble gases are a group of elements that are known for their lack of reactivity and are unique in the periodic table because they are practically inert. This group consists of helium, neon, argon, krypton, xenon, and radon. Mendeleev did not include these elements in his original periodic table because most were not discovered at the time.

The noble gases are located in Group 18 of the periodic table. They are characterized by their full valence electron shells, which account for their minimal chemical reactivity. This property makes them highly stable compared to other elements.

• Their lack of reactivity means they rarely form compounds with other elements.
• Noble gases have various applications, including in lighting, welding, and as coolants in nuclear reactors.

Understanding these gases was pivotal in broadening our comprehension of elemental properties and chemistry's complex nature.

history of chemistry

The history of chemistry is rich with discoveries and advancements that have shaped our modern understanding of elements and compounds. Chemistry evolved significantly during the 19th century, with many scientists making groundbreaking discoveries.

One of the central advancements was the development of the periodic table by Dmitri Mendeleev in 1869. Mendeleev's periodic table was revolutionary because it organized known elements by atomic mass and chemical properties, allowing for the prediction of new elements. This approach highlighted the periodic law and served as a robust framework for future discoveries.

• Mendeleev's periodic table addressed the systemic organization of elements, predicting elements like gallium and germanium, which were discovered later.
• Each discovery in chemistry built upon prior knowledge, leading to a cumulative enhancement of the field.

Mendeleev's work exemplifies how chemistry has progressed from the study of alchemical elements to a precise scientific discipline, allowing us to explore the complexities of the natural world.