For example he arranged Co, Ni, Pd, Pt and Ir which have different properties compared with halogens in the same row (F, Cl, Br, I). (see Newlands’ first horizontal row)
Newlands periodic table was restricted to only 56 elements and did not leave any room for new elements. Elements that were discovered later could not be fitted into Newlands table in accordance with their properties
Newlands attempted to link the periodicity of the chemical properties of elements with the periodicity found in the music. In musical scale any note in a key is separated from its octave by an interval of seven notes. This must have made him to force all the elements into this active pattern sometimes without caring the similarities.
Mendeleeff arranged the elements known at that time
in a
chart in a systematic order in the increasing order of
their atomic weights refer to table 2 the modified
Mendeleef’s periodic table 2a . He divided the chart into 8
vertical columns known as groups. Each group is divided
into A, B sub groups. Each column contained elements of
similar chemical properties. It is said that elements in a
group have similer properties and elements along periods
(horizontol rows) have diffrent properties.
The elements in the first column, for example, react with oxygen to form compounds with the general formula R2O. For example, Li, Na and K when react with oxygen and form compounds Li2O, Na2O and K2O respectively
Elements of the second column react with oxygen to form compounds with the general formula RO. For example, Be, Mg and Ca when react with oxygen form BeO, MgO and CaO.
Mendeleeff tried to explain the similarities of elements in the same group in terms of their common valency.