because they didn't react because they have stable valence shells
Mendeleev predicted that properties of elements are periodic function of atomic mass. He demonstrated it by creating a table.
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Mendeleev's periodic table arranged elements by increasing atomic mass and grouped elements with similar properties together. Today's periodic table is similar, but it is arranged by increasing atomic number, which reflects the number of protons in an atom's nucleus. Both tables also show periodic trends in properties as you move across and down the table.
The bottom section of the periodic table is for the lanthanides and actinides, which are also known as the inner transition metals. These elements are placed below the main body of the periodic table to keep it compact, as they would otherwise disrupt the table's organization.
A reasonable value for the atomic mass of the missing element can be estimated by finding the average atomic mass of the elements on either side of the missing element in the periodic table. This estimation assumes a gradual increase in atomic mass across the periods in the table.
To understand the concept of Periodic Table
In Mendeleev's periodic table, the elements were arranged in the increasing order of their atomic masses and repeating periodic properties.
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Mendeleev predicted that properties of elements are periodic function of atomic mass. He demonstrated it by creating a table.
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Actually, Dmitri Mendeleev formulated the periodic law and published his periodic table of elements in 1869. This table arranged elements by increasing atomic mass and grouped them based on similar properties, predicting the properties of missing elements. It was a significant contribution to the field of chemistry.
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Dmitri Mendeleev was a Russian chemist; he proposed the modern Periodic Table of elements in 1869.
Mendeleev's periodic table arranged elements by increasing atomic mass and grouped elements with similar properties together. Today's periodic table is similar, but it is arranged by increasing atomic number, which reflects the number of protons in an atom's nucleus. Both tables also show periodic trends in properties as you move across and down the table.
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The noble gases group is missing from John Newlands' periodic table. The noble gases were not discovered until after Newlands proposed his periodic table in 1864.