What is Newlands' Law of Octaves ? What were the limitations of Newlands' Law of
Octaves ?
Answers
Answer:
On the basis of this observation, Newland’s law of octaves was formulated. The law of octaves states that every eighth element has similar properties when the elements are arranged in the increasing order of their atomic masses.
Limitations of Newland's Law of Octaves: Newland could arrange elements only up to calcium, out of the total 56 elements known. After calcium, every eighth element did not possess properties similar to that of the first. Only 56 elements were known at the time of Newlands, but later several elements were discovered.
NEWLANDS LAW OF OCTAVES
Explanation:
The Newlands law of octaves states that when elements are arranged in the increasing order of atomic weights, every eighth element has similar properties to the first. In other words, the properties of elements are repeated after every seventh interval.
Newlands arranged 56 elements (hydrogen to thorium) known at that time in the increasing order of atomic weights. He observed the periodicity in the arrangement.
The table below is from Newlands' publication of 1865. He ordered the elements from the top to bottom in the increasing order of atomic weights. The numbers in the table are not atomic weights but ordering numbers.
Newlands' law of octaves
Order No. Element Order No. Element Order No. Element Order No. Element Order No. Element Order No. Element Order No. Element Order No. Element
1 H 8 F 15 Cl 22 Co & Ni 29 Br 36 Pd 42 I 50 Pt & Ir
2 Li 9 Na 16 K 23 Cu 30 Rb 37 Ag 44 Cs 51 Os
3 Be 10 Mg 17 Ca 24 Zn 31 Sr 38 Cd 45 Ba & V 52 Hg
4 B 11 Al 19 Cr 25 Y 33 Ce & La 40 U 46 Ta 53 Tl
5 C 12 Si 18 Ti 26 In 32 Zr 39 Sn 47 W 54 Pb
6 N 13 P 20 Mn 27 As 34 Nd & Mo 41 Sb 48 Nb 55 Bi
7 O 14 S 21 Fe 28 Se 35 Ro & Ru 43 Te 49 Au 56 Th
According to the law of octaves, every eighth element in the above table must share similar physical and chemical properties. Thus, each element in the same row must have similar physical and chemical properties. But this is not true. The periodicity is only valid till calcium. An example of this is lithium, sodium, and potassium; they share physical and chemical properties. The remaining elements after potassium, (Cu, Rb, Ag…) are different and do not show similarities to the former elements. This is because the law of octaves fails to incorporate transition metals.
In the previous table, several elements are missing, particularly the noble gases—He, Ne, Ar, Kr, Xe, and Rn. The reason is they were not discovered. Also, the ordering becomes inconsistent after calcium, for example, the position of Ti and Cr is interchanged. Some elements were placed in the same position (Co & Ni, Ce & La, Nd & Mo…). The other thing to notice is that elements are ordered from top to bottom which is the transpose of the modern periodic table where the ordering is from the left to right.