Dobereiner's Triads

Q.

What Is Atomic Mass And Average Atomic Mass?

Q.

What is Debereiner’s law of triads? Explain with the help of one example of a Dobereiner’s triad.

Q.

What were the limitations of Dobereiners classification?

Q.

State one example of a Dobereiner’s triad, showing in it that the atomic mass of the middle element is half-way between those of the other two.

Q.

Is there any tricks to memorize the whole periodic table with atomic numbers and valencies?

Q.

If Cl, Br, I, is a Dobereiner's triad and the atomic masses of Cl and I are 35.5u and 127u respectively, then the atomic mass of Br is

1. 162.5

2. 91.5

3. 81.25

4. 45.625

Q.

Do atoms normally exist in free state? Why not? If not, how do they exist? If yes, explain? [3 MARKS]

Q.

Which among the following group of elements does not form a Dobernier triad?

1. Sr, Ba, Ca

2. Br, Cl, I

3. Cl, Br, I

4. Li, K, Na

Q.

The three imaginary elements X, Y and Z represent a Dobernener’s triad. If the atomic mass of element X is 14 and that of element Y is 46, then the atomic mass of element Z will be :

(a) 28 (b) 60 (c) 78 (d) 72

Q.

What is a triad?

Q.

Name the scientists who gave the following laws in the early classification of elements:

(a) Law of octaves (b) Law of triads

Q.

If chlorine, bromine and iodine form a Dobereiner's triad and the atomic masses of chlorine and iodine are 35.5 u and 127.0 u respectively, then the atomic mass of bromine is _____.

1. 162 u

2. 91 u

3. 81 u

4. 45 u

Q.

Give reason for the need of classification of elements. [2 MARKS]

Q.

Which of the following weigh the most?

1. 0.5 mole of carbon

2. 3.011×10²⁴ atoms of nitrogen

3. 6.022×10²³ formula units of calcium carbonate

Q.

Given below are the elements with their atomic masses. Identify a set of elements which is not a Dobereiner's triad.

1. Cl (35.5), Br (79.9), I (126.9)
2. Ca (40.1), Sr (87.6), Ba (137.3)
3. Li (6.9), Na (23.0), K (39.0)
4. N (14.0), P (31.0), As (74.9)

Q.

Dobereiner's triad arranged the elements with similar properties into:

1. Periods

2. Groups

3. Both period and group

4. None of these

Q.

Can the following groups of elements be classified as Dobereiner’s triads?

(a) Na, Si, Cl (b) Be, Mg, Ca

Give the reason for your answer.

(Atomic masses : Be = 9; Na = 23; Mg = 24 ; Si = 28 ; Cl = 35.5; Ca = 40)

Q.

Why was the system of classification of elements into triads not found suitable?

Q. Dobereiner suggested that properties of elements are related to their _______.

1. atomic numbers
2. atomic masses
3. number of electrons
4. atomic sizes

Q. Which of the following set of elements do not form a Döbereiner’s triad?

1. Calcium, strontium, and barium
2. Carbon, nitrogen, and oxygen
3. Lithium, sodium, and potassium
4. Bromine, chlorine, and iodine

Q. Which of the following set of elements do not form a Döbereiner’s triad?

1. Carbon, nitrogen, and oxygen
2. Calcium, strontium, and barium
3. Bromine, chlorine, and iodine
4. Lithium, sodium, and potassium

Q.

Three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called? Give one example of such a set of elements. [2 MARKS]

Q.

State the merits of Mendeleev's classification of elements.

Q. Dobereiner made groups of elements, having similar chemical properties and called them _______.

1. trio
2. tetrads
3. triads
4. dyads

Q.

A, B and C are the elements of a Dobereiner’s triad. If the atomic mass of A is 7 and that of C is 39, what should be the atomic mass of B ?

Q.

Question 1
Did Dobereiner's triads also exist in the columns of Newlands' octaves? Compare and find out.

Q. Döbereiner arranged the elements in triads in the increasing order of their .

1. atomic masses
2. valency
3. atomic numbers

Q.

(a) Did Dobereiner’s triads also exist in the columns of Newland’s law of octaves? Explain your answer.

(b) What were the limitations of Dobereiner’s classification of elements?

(c) What were the limitations of Newland’s law of octaves?

Q. Based on Dobereiner's theory of triads, match the following.
Element (atomic mass)

1. X : Br
2. Y: Na
3. Z: Sr

Q. Atomic mass of X and Z are 20 u and 40 u respectively. If X, Y and Z constitute Dobereiner’s triads, what should be the atomic mass of Y (in $u$)?

1. 40
2. 30
3. 60
4. 20