Question

why r theelements Cl,Br,I called halogens?

why are the elements calcium strontium barium named as alkaline earth metals?

why did newland's octave work only with light elements?

Answer 1

Part-I
Halogen means salt former. Since many elements of group 17 have a tendency to exit in the form of salt or either they have tends to form salt such as NaCl, NaF etc. that is why the elements such as Cl,Br,I of group 17 are called halogens
Part-II
The elements in the group include Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra) are named so because elements have its slight solubility in water due to which the name "Alkaline", is given and secondly elements have inability to decompose when exposed to heat. Hence name earth is given. Hence elements in Group 2 are known as the Alkaline Earth Metals.
Part -III
According to newland's octave when the elements are arranged in the order of increasing atomic weight, they show similar chemically and physically properties of all arranged elements which is same as in musical scales'. However this failed for heavier elements due to their very large size and weight and theory failed to continue.