Question

Initially, it was believed that the atomic mass of beryllium was 13. But Mendeleev suggested that its atomic mass should be 9.
A.Was Mendeleev suggestion correct
B.How had he reached this conclusion

Answer 1

To answer this question, you should recall the formation of the periodic table. Mendleev’s periodic table was based on the properties that chemical properties of an element are dependent on their atomic mass. Thus, elements with similar properties were assigned atomic mass numbers and placed together in the periodic table.

Complete step by step answer:
-Yes, the suggestion of Mendeleev was correct. The reason for this was initially hydrogen was considered as the standard to find the masses of different elements but this consideration was unable to provide the correct value of masses of different elements.
-After hydrogen, oxygen was considered as the standard to find the masses of different elements but in this consideration, the same problem arose. Finally, the isotope of carbon with atomic mass 12 was considered as the standard to find the masses of different elements. Through this method, the correct values of masses of different elements were obtained.
-Most of Mendeleev's suggestion was based on assumption. There was no experimental proof for his suggestions. He changed the atomic mass of Be to 9 and placed it above Mg in his table which was later found to be correct. He had made this change because the physical and chemical properties of Be and Mg were the same. Later these elements were named as alkaline earth metal.
So Mendeleev’s suggestion was correct.

Note:
There are 4 blocks in the periodic table: s-block, p-block, d-block and f-block. All of the s-block elements are metals. Usually, they are shiny, silvery, good conductors of heat and electricity, and lose their valence electrons easily. The p-block due to its ability to accommodate a large number of electrons. It has the biggest variety of elements and is the only block that contains three types of elements: metals, nonmetals and metalloids. d-block elements have properties that are between s-block elements and p-block elements properties. It consists of transition metals. The f-block elements are mostly radioactive. The block names were created to represent the quality of the spectroscopic lines of the atomic orbitals.