class 10 science periodic Classification of Elements NCERT Notes For Class 10
- Classification means identifying similar species and grouping them together.
- Lavoisier divided elements into two main types known as metals and non-metals.
- Doberiner’s Law of Triads: According to this law, “in certain triads (grout) of three elements) the atomic mass of the central element was the arithmetic mean of the atomic masses of the other two elements.” But in some trials all the three elements possessed nearly the same atomic masses, therefore the law was rejected.
e.g., atomic masses of Li, Na and K are respectively 7, 23 and 39, thus the mean of atomic masses of I St and 3rd element is
Limitations of Doberiner’s Triads: He could identify only a few such trials and so the law could not gain importance. In the triad ofFe, Co, Ni, all the three elements have a nearly equal atomic mass and thus does not follow the above law
Newland’s Law of Octaves:
According to this law “the elements are arranged in such a way that the eighth element starting from a given one has properties which are a repetition of those of the first if arranged in order of increasing atomic weight like the. eight note of a musical scale.”