Question

Study the data of the following three categories;
Category Name. Atomic mass
A. Li. 7
Na 23
K 39
B. N. 14
P. 31
As. 74
C. B 10.8
Al 27
Ga 69.7
1. From the given three categories, pick the one which form dobereiner’s triads?
2. Why did mendeleev placed elements of category A,B,C in three diff groups?
3. Is newland’s law of octaves applicable to all three categories? Give reasons?

Answer 1

Answer:

li na k are dobereiners triads.

Answer 2

1. The category which forms Dobereiner's triads is  A. Li , Na , K

2. Mendeleev placed elements of category A,B,C in three diff groups because they have different  properties.

3. No, Newland's Law of octaves is not applicable for all three categories.

• Dobereiner's triads should follow the rule of " the second element of the triad should have molar mass of mean of molar masses of the other two elements".
• Li-7,  Na-23 K-39       Na-23 = (Li-7 + K-39)/ 2
• P-31 ≠ (N-14 + As-74) /2    ,
• Al - 27 ≠ (B- 10.8 + Ga-69.7 ) / 2
• Mendellev's law for periodic table states that periodic properties of the elements are funtions of their atomic masses.
• Newland's Law of octaves states that the eight element from a element possess same properties.
• Na is eight element from Li, also K is eighth element from Na.
• P is eight element from N, but P is not eighth element from N.
• Al is eighth element from B, but Ga is not eighth element from Al.