(a) John Newland proposed the Law of octaves and it states that when elements are arranged in the order or increasing atomic masses, the properties of the eighth element are a repetition of the properties of first element.
(b) Dobereiner's law of triads: When elements are arranged in order of increasing atomic masses groups of three elements(triads), having similar chemical properties are obtained. The atomic mass of the middle elements of the triad being equal to the arithmetic mean of the atomic masses of the other two elements.
For example: Alkali metal group (Dobereiner's triad) : Lithium is the 1st element, sodium is the middle element whereas potassium is the 3rd element of the triad.
