Tag: dobereiner's triads

Questions Related to dobereiner's triads

If three elements X, Y, and Z form a Dobereiner's triad and atomic weights of X and Z are 9 and 40 respectively, then the atomic weight of the element Y is approximately:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. 24.5

  2. 49

  3. 34.5

  4. 29

Show answer
Correct Option: A
Explanation:

According to Dobereiner, the atomic weight of the central element of the triad is the arithmetic mean of the atomic weights of the other two members. 


Therefore, atomic weight of Y = $\cfrac{9 + 40}{2} = 24.5\ g$


Hence, option A is correct.

Law of Triad was proposed by:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. Newland

  2. Gay Lussac

  3. Mendeleev

  4. Dobereiner

Show answer
Correct Option: D
Explanation:

Dobereiner, in 1817 suggested a relationship between the properties of elements and their atomic weights. According to Dobereiner, the atomic weight of the middle element is nearly the same as average of the atomic weights of other two elements.

The element in between lithium and potassium in Dobereiner's classification is:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. Mg

  2. Na

  3. Ca

  4. Rb

Show answer
Correct Option: B
Explanation:

Li, Na, K formed a Dobereiner's triad. Thus the element between Lithium and potassium is Sodium (Na).

Chlorine, Y and Iodine form a Dobereiner's triad. Identify the atomic weight of Y.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. 162.5

  2. 81.25

  3. 121.5

  4. 90.5

Show answer
Correct Option: B
Explanation:
Cl, Y and I for Dobereiner's triad. Thus weight of Y is arrange of weight of Cl and I
$\therefore$ Atomic weight of Y is $\cfrac { 35.5+127 }{ 2 } =81.25$

Three elements X, Y and Z form a Dobereiner triad. The ratio of the atomic weight of X to that of Z is 7: 25.


 If the sum of the atomic weights of X and Z is 160, find the atomic weights of X, Y and Z.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. X $\rightarrow$ 35, Y $\rightarrow$ 80, Z $\rightarrow$ 125

  2. X $\rightarrow$ 125, Y $\rightarrow$ 80, Z $\rightarrow$ 35

  3. X $\rightarrow$ 80, Y $\rightarrow$ 35, Z $\rightarrow$ 125

  4. X $\rightarrow$ 80, Y $\rightarrow$ 125, Z $\rightarrow$ 35

Show answer
Correct Option: A
Explanation:
Let weight of X be $7a$  $\therefore$ Atomic weight of $Z=25a$

$\therefore7a+25a=160$

$\Rightarrow a=5$

Weight of X$=35$ and of Z is $125$

Atomic weight of Y is arranged of X and $2=\cfrac { 35+125 }{ 2 } =80$

Hence, the correct option is $\text{A}$

When a Dobereiner triad is considered, the sum of atomic weights of extreme elements X and Z is 177.6 and difference of Z and Y is five times the number of protons present in a neon atom. Identify X, Y and Z.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $X \rightarrow Ca, Y \rightarrow Sr, Z \rightarrow Ba$

  2. $X \rightarrow Li, Y \rightarrow Na, Z \rightarrow K$

  3. $X \rightarrow K, Y \rightarrow Rb, Z \rightarrow Cs$

  4. $X \rightarrow Sr, Y \rightarrow Ba, Z \rightarrow Ra$

Show answer
Correct Option: A
Explanation:
The atomic weight of Y is avergae of X and Z
$\therefore { M } _{ Y }=\cfrac { 177.6 }{ 2 } =88.8$
$88.8$ is weight of Sr. So Y is Sr. According to this only option A is correct.

Which of the following sets of atomic masses do not correspond to Dobernier traid?

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $7, 23, 39$

  2. $20, 38, 56$

  3. $47, 91, 178$

  4. $54, 95, 183$

Show answer
Correct Option: C,D
Explanation:

The following sets of atomic masses do not correspond to Dobernier traid.
(C) $\displaystyle 47, 91, 178$
(D) $\displaystyle 54, 95, 183$
In these sets, the atomic mass of middle element is not equal to the mean of atomic masses of first and last element.
$\displaystyle 91 \neq \dfrac {47+178}{2}$
$\displaystyle 95 \neq \dfrac {54+183}{2} $

Dobereiner was the first person to illustrate the relationship between the ____________ of elements and their properties.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. atomic masses

  2. electron negativity

  3. molecular masses

  4. number of protons

Show answer
Correct Option: A
Explanation:

Dobereiner grouped elements in set of triads. Thus each group had 3 elements. Dobereiner classified elements into groups based on their properties. He illustrate the relationship between the atomic masses of elements and their properties with his law of triads.

Which of the following statements is not true about Dobereiner's law of triads?

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. The law was applicable to all known elements

  2. Nitrogen family does not obey the law of triads

  3. Dobereiner's classification was not very useful

  4. The atomic mass of the central element of each triad was merely the arithmetic mean of of the atomic masses of other two elements

Show answer
Correct Option: A
Explanation:
Döbereiner’s triads could find only three triads; .i.e total of 9 elements only but there were many more elements known at that time.

Therefore Dobereiner’s could not classify most of the elements known at that time.

Hence, the correct option is $A$

In a triad of $A, B, C$ elements if the atomic masses of $A$ and $C$ respectively are $100$ and $200$, then the atomic mass of $B$ is:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $300$

  2. $175$

  3. $125$

  4. $150$

Show answer
Correct Option: D
Explanation:

According to Dobereiner's law of traid, the average of the masses of the first and the last element is equal to the atomic mass of the middle element. So, $\dfrac{100+200}{2}$ = 150. Hence, the atomic mass of B is 150.


Hence, the correct option is $\text{D}$