Question

define periodicity, give its causes ​

Answer 1

Answer:

The trend of similar properties that are observed in elements, when arranged or positioned with increasing order of atomic number called periodicity. The cause for the periodicity is the valence electrons of elements. ... Thus, members of a group show similar chemical properties, because of which they show periodicity

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Answer 2

$\huge\bf\underline{Answer}$

Periodicity is the quality or character of being periodic; the tendency to recur at intervals.

$\huge\bf\underline{Causes \: - }$

The cause of periodicity is the recurrence of similar electronic configuration i.e. same number of electrons in the outermost orbit.In a particular group, electrons in the outermost orbit remain the same i.e. electronic configuration is similar.