Question

Initially It was believed that atomic mass of beryllium was 13. But Mendeleev suggested that its atomic mass should be 9. 

(i) was Mendeleev suggestion correct? 

(ii) How had he reached to this Conclusion?

Answer 1

(i) yes, Mendeleev’s suggestion was correct as it was found later on experimentally that beryllium’s atomic mass is 9. 

(ii) He studied the formula of hydrides and oxides of beryllium and observed that they had similarity with those of magnesium oxides and hydrides. Thus he placed the beryllium above Mg and predicted its atomic mass as 9.