Question

what was the basis of the earliest attempts made for classification in groups of elements

Answer 1

   The basis of earliest attempts for classification of elements was the chemical and physical properties observed by the scientists.  Some reactions with known elements and compounds were compared.
 
   The atomic weights were used to order them.  To group them into groups they tried to observe the periodicity of the properties as the atomic weight increases.

Law of triads and then law of octaves were proposed.  Doberneiner , Chancourtois and Newlands proposed these laws and prepared some tables.

Answer 2

in the beginning, attempts were made by chemist to classify elements on the basis of factors such as density,malleability, ductility, etc.,and also considere whether they where
metals or nonmetals.