The missing elements in the Periodic Table?

[FantasyQueen]

How did Dimitri Mendeleev know that some of the elements were missing/not discovered? How did he know that the missing elements existed? Did he find some sort of pattern when he created the Periodic Table?

 

[Borek]

Pattern - yes. Google for ekaboron.

 

[Ygggdrasil]

Here's an interesting anecdote about an argument between Mendeleev and the Paul Emile François Lecoq de Boisbaudran, the person who discovered Gallium (one of the missing elements whose existence Mendeleev predicted):

Mendeleev picked apart Lecoq de Boisbaudran's data on the new element (soon named gallium). Mendeleev claimed, largely without evidence, that the accomplished Lecoq de Boisbaudran must have made mistakes when measuring gallium's weight and density, since they differed from Mendeleev's predictions.

The chutzpah here is incredible, but Mendeleev tended to trust his own instincts and formulas over mere evidence. Crackpots often do. The difference between Mendeleev and most crackpots is that Mendeleev was right: Lecoq de Boisbaudran soon had to publish an embarrassing retraction about gallium's weight and density, changing them to values that vindicated Mendeleev. According to science philosopher and historian Eric Scerri, "The scientific world was astounded to note that Mendeleev, the theorist, had seen the properties of a new element more clearly than the chemist who had discovered it."

http://www.slate.com/id/2258112/entry/2257317/

 

[Dr Lots-o'watts]

How did Dimitri Mendeleev know that some of the elements were missing/not discovered? How did he know that the missing elements existed? Did he find some sort of pattern when he created the Periodic Table?

Doesn't the word "Periodic" imply a pattern? I'm not familiar with the exact history, but I would assume that once periodicity is noted, you just have to fill in the blanks to "discover" new elements. Given a table at this stage:

http://www.click4chill.com/wp-content/uploads/2010/07/periodic_table.gif

It seems to me that it isn't rocket science to predict the existence of element 113.

Perhaps Medvedev's most astounding feat was to note a periodicity in the properties of the then-discovered elements.

 

[LudusRex]

I can provide some insights into the missing elements in the Periodic Table and how Dimitri Mendeleev knew about them.

Firstly, it is important to understand that the Periodic Table is a systematic arrangement of all the known chemical elements according to their atomic structure and properties. When Mendeleev first created the Periodic Table in 1869, there were only 63 known elements. However, he noticed that there were several gaps or missing elements in his arrangement.

Mendeleev was able to predict the existence of these missing elements based on his understanding of the periodicity of the elements. He observed that there were certain patterns in the properties of the known elements, such as atomic mass and chemical reactivity, which repeated at regular intervals. This led him to believe that there were still undiscovered elements that would fit into these patterns.

Mendeleev also used the concept of periodicity to predict the properties of the missing elements. For example, he predicted the existence of an element with an atomic mass of 72, which he called eka-aluminum. This element was later discovered and named gallium, and its properties matched Mendeleev's predictions.

So, how did Mendeleev know that the missing elements existed? He used a combination of empirical evidence, intuition, and mathematical reasoning to make these predictions. He also collaborated with other scientists and regularly updated his Periodic Table as new elements were discovered.

In conclusion, Mendeleev's understanding of the periodicity of elements and his ability to predict the properties of the missing elements were crucial in his creation of the Periodic Table. His work laid the foundation for further discoveries and advancements in the field of chemistry.