Question

all Acheivements of modern periodic table

Answer 1

a) Achievements of Modem periodic table are:
(i) Prediction of properties of elements could be made with more precision since elements were arranged on the basis of increasing atomic number.
(ii) Metals are separated from non-metals by a zig-zag line. On this zig-zag line borderline elements-like Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Polonium which are also known as metalloids are present.

Answer 2

1.Isotopes of the same elements had different atomic masses but same atomic number hence the occupy the same place in the modern periodic table.
2. when elements are arranged according to their atomic number various animal is regarding the pairs of certain elements in Mendeleev periodic table disappears for example the atomic no. of Cobalt and Nickel is 27 and 28 resp. hence Cobalt will come first due to it's atomic no. although it's atomic mass is greater.
3.Elements are classified into different blocks according to their electronic configuration.