Bases ,advantages and drawbacks of dobereiner's triads,newland law of octaves,and mandaleev's classification of elements
Answers
Law : According to Dobereiner, all elements occurred in groups of three, when arranged in increasing order of atomic masses. He referred to these groups as triads. In a traid the elements had similar chemical properties. Traids of the Dobereiners classification: Traid1:
Element
Atomic mass
Lithium (Li)
7
Sodium (Na)
23
Potassium (K)
39
LIMITATIONS :
#Dobereiner could find only three triads; .i.e total of 9 elements only.
#However the total number of elements were more than that of those encompassed in Dobereiner’s Triad.
Thus, Dobereiner’s could not be classify most of the elements known at that time.
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Newlands Law of octaves
Law: in 1866 John newland an English scientist arrange the known elements in order of increasing atomic masses and found that every 8 th element had properties similar to that of the first . He compared this to the octaves found in music that is sa,re,ga,ma,pa,dha,ni and in west they use notations do ,re ,MI ,FA ,so ,La, ti. Therefore he called it the law of octaves.
LIMITATIONS:-
*This logos applicable only upto calcium after calcium every 8th element do not possess the same properties similar to the first.
*That there were only 56 element existed in nature and element would be discovered in the future but this but this fact proof totally wrong.
*In order to fit element in his table newland adjusted new elements Cobalt and Nickel in the same slot and the same column with fluorine ,chlorine and bromine which have very different properties.
*This worked with lighter elements only.
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Mendeleev's periodic table
Law: "the physical and chemical properties of an element are the periodic function of the atomic masses"
Achievements: mendeleev's periodic law predicted the existence of some elements that have not been discovered at that time like gallium scandium and Germanium he named them as Eka-boron,eka-aluminium and eka-silicon.
*Periodic table could accomodate noble gases when they were discovered they were discovered.
LIMITATIONS:
1). Mendleeve could not assign the correct position of hydrogen in his table.
2). Position of isotopes could not be explained in his table.
3). The atomic masses do not increase in regular manners in going from one element to the next .
example Cobalt have the atomic mass of 58.9 comes first and Nickel has atomic mass of 58.7 comes later