Question

In Mendeleev's periodic table gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later?

• A. Germanium
• B. Chlorine
• C. Oxygen
• D. Silicon

Answer 1

The correct option is A

Germanium

1. A Russian chemist Dimitri I Mendeleev stated in 1869 that “the physical and chemical properties of elements are the periodic functions of their atomic masses.”
2. Mendeleev then arranged all the elements known at that time in order of increasing atomic masses.
3. The arrangement was done in horizontal rows and vertical columns in such a way that the elements with similar properties belong to the same group.
4. There were many merits of the Mendeleev's periodic table,

• The periodic table which was initially limited to just 8 groups, was then generalized by Mendeleev.
• Gaps were left in the periodic table by Mendeleev for the subsequent inclusion of elements not known at the time based on the idea that these elements will be discovered later.
• He also predicted the properties of the elements based on the properties of elements lying beside the vacant slot.
• For example, Eka-aluminum which was placed one place below aluminum in the periodic table, its chemical properties and atomic mass, density, and valency were quite similar to those of the element Gallium (Ga) discovered later.

Property	Eka-aluminum	Gallium
At. mass	68	69.7
MP	5.9 g/cc	5.5 g/cc
Valency	3	3
Formula of Oxide	$M_2{O}_3$	$G{a}_2{O}_3$

Property	Eka-silicon	Germanium
At. mass	72	72.6
MP	5.5 g/cc	5.36 g/cc
Valency	4	4
Formula of Oxide	$M{O}_2$	$Ge{O}_2$

The correct option would be (A) Germanium and (B), (C) and (D) are incorrect.