Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Scandium and germanium
Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the following elements :
$K,\, C,\, Al,\, Si,\, Ba$.
In the Modern Periodic Table, calcium (atomic number $20$) is surrounded by elements with atomic numbers $12$, $19$, $21$ and $38$. Which of these have physical and chemical properties resembling calcium?
Which element has
$(a)$ two shells, both of which are completely filled with electrons?
$(b)$ the electronic configuration $2,\,8,\,2 ?$
In the Modern Periodic Table, which are the metals among the first ten elements ?
What were the criteria used by Mendeléev in creating his Periodic Table ?
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