(a) The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all the three attempts. (b)Name the scientists who first of all showed that atomic number of an element is a more fundamental property than its atomic mass. 5 (c) State Modern Periodic law.
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a) Advantage :-
Doberiner : He made chemists look at elements in terms of groups of elements with similar chemical and physical properties.
Newland : He links the elements' properties to their atomic masses.
Mendeleev : He could predict the existence of other elements and could predict their properties so, as to leave space in the periodic table.
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a) Advantage:
Dobereiner: He could arrange the elements with similar properties into groups having three elements known as Triads.
Newland: When elements were arranged in the increasing order of atomic masses, properties of every 8th element were similar to the 1st element, just as in octaves of music
Mendeleev: Mendeleev’s periodic law predicted the existence of some elements that had not been discovered at that time.
Limitation:
Dobereiner: Not all the elements discovered at that time could be grouped in triads.
Newland: The law of octaves was applicable till calcium.
Mendeleev: Isotopes of elements were discovered later which violated Mendeleev’s periodic law.
b) Henry Moseley was the first scientist who showed that an atomic number of an element is a more fundamental property than its atomic mass.
c) Modern Period law:
Properties of elements are a periodic function of their atomic numbers.