In the Modern Periodic Table, which are the metals among the first ten elements ?
Among the first ten elements, lithium $(Li)$ and beryllium $(Be)$ are metals.
Nitrogen (atomic number $7$) and phosphorus (atomic number $15$) belong to group $15$ of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Compare and contrast the arrangement of elements in Mendeléev’s Periodic Table and the Modern Periodic Table.
What were the criteria used by Mendeléev in creating his Periodic Table ?
Why do you think the noble gases are placed in a separate group ?
Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
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