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Mendeleev grouped the elements in series according to their properties and atomic weight. His rule of thumb of giving priority to chemical properties, among other effects, left him with spots where he couldn't insert any of the elements known in his time -- germanium ang gallium come to mind. In group IIIa between aluminum and indium, and in group IVa between silicon and tin, there should have been two other elements, with properties intermediary between those of Al and In, respectively Si and Sn. Given that no such elements were known at the time, he left the spots empty, predicting that they will be discovered in the future, and called the two missing elements eka-aluminium ("similar to aluminum") and eka-silicium ("similar to silicon"). As it happens, he was right!
Those empty spots are where the question marks go. Of course, using a question mark is not mandatory -- anything that can be understood as "something is missing here" will do.
As a side note, these two were by far not the only "missing" elements when Mendeleev initially published his Periodic Table. Many of the places of transitional elements, discovered later, would have been "question marks", including all transuranic and transplutonic ones (which are artificial, synthesized only in the 20th century), as well as most the heavier radioactive elements in the main groups (francium, radium, polonium, astatine, radon etc.).
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What was Dmitri Mendeleev first periodic table called?
Dmitri Mendeleev first periodic table is called Mendeleev's periodic table. Elements are arranged according to atomic mass.
Who is considered to be the father of the periodic table?
Dmitri Mendeleev is considered the father of the periodic table. He created the first widely accepted version of the periodic table in 1869, arranging elements based on their properties and atomic weights. Mendeleev's table laid the groundwork for the modern periodic table.
What was the first periodic table?
Hydrogen is the first chemical element in the Periodic Table of Mendeleev.
Which scientist did periodic table of elements?
Dmitri Mendeleev is credited with developing the periodic table of elements in 1869. He arranged the elements by increasing atomic mass, grouping together elements with similar properties. Mendeleev's table formed the basis for the modern periodic table.
In what century was the periodic table set up?
The periodic table was set up in the 19th century, specifically in 1869 by Dmitri Mendeleev. Mendeleev organized the elements based on their properties and atomic weights, creating the foundation for the modern periodic table.
What year did mendeleev publish periodic table?
Mendeleev's published the periodic table in 1869.
What did the Russian scientist Mendeleev create the periodic table?
Dmitri Mendeleev created the periodic table to organize and classify the known elements based on their properties and atomic weights. He left gaps for undiscovered elements and successfully predicted the properties of some of these missing elements.
What year did Mendeleev's publish the periodic table?
Mendeleev's published the periodic table in 1869.
What is the first element of the Mendeleev's periodic table?
The first element of the Mendeleev's periodic table is hydrogen (H).
What year did Dmitri mendeleev pubish the periodic table?
In the yer 1869, Mendeleev published the periodic table.
What was Dmitri Mendeleev first periodic table called?
Dmitri Mendeleev first periodic table is called Mendeleev's periodic table. Elements are arranged according to atomic mass.
What did mendeleev did?
the Periodic Table.
What did Mendeleev develop?
Mendeleev was a Russian chemist who organized the periodic table.
Who is considered to be the father of the periodic table?
Dmitri Mendeleev is considered the father of the periodic table. He created the first widely accepted version of the periodic table in 1869, arranging elements based on their properties and atomic weights. Mendeleev's table laid the groundwork for the modern periodic table.
Why did Mendeleev's periodic table not contain the noble gases?
Because noble gases were not discovered when Mendeleev formulated his periodic table
In What century did mendeleev organize the periodic table?
In 19th century , Mendeleev organised periodic table. He organised it in year 1869.
Was helium included in Mendeleev's original periodic table?
No, he did not know about it. Helium was discovered in spectrographs of the Sun in 1868 and isolated in 1895. Mendeleev's original table skipped from hydrogen (1) to lithium (3).
