Tag: dobereiner's triads

Questions Related to dobereiner's triads

Which of the following triads does not follow Dobereiner's law of triads?

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

  1. Li, Na, K

  2. Ca, Sr, Ba

  3. Be, Mg, Ca

  4. Cu, Ag, Au

Show answer
Correct Option: D
Explanation:

Since the atomic weight of Ag is not equal to the mean of the atomic weights of Cu and Au.


Thus, (Cu, Ag, Au) triad do not follow Dobereiner's law of triads.

Option D is correct.

Which of the following set of elements cannot be a triad?

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

  1. $Li, Na, K$

  2. $B, Al, Ga$

  3. $Be, Mg, Ca$

  4. $Cl, Br, I$

Show answer
Correct Option: B
Explanation:

Triad can be only when the middle element is having mean atomic weight of other two elements $,$ which $B, Al, Ga$ does not have such triad$.$

Which of the following elements follow Dobereiner's law of Triads?

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

  1. Na = $23$, Li = $7$ and K = $39$

  2. Cl = $35$, Br = $80$ and F = $19$

  3. Ca = $40$, Mg = $24$ and Sr = $88$

  4. Na = $23$, K = $39$ and Rb = $85$

Show answer
Correct Option: A
Explanation:

According to Dobereiner's, the atomic weight of the middle element is nearly the same as the average of the atomic weights of the other two elements.


$Li(7)+K(39)\longrightarrow \cfrac{7+39}{2}=Na(23)$

So, $Na=23, Li=7$ and $K=39$ 

The correct option is ( A ) 

Following triads have approximately equal size

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

  1. ${ Na }^{ + },\quad { Mg }^{ 2+ },\quad { Al }^{ 3+ }$

  2. ${ F }^{ - },\quad Ne,\quad { O }^{ 2- }$

  3. $Fe,\quad Co,\quad Ni$

  4. ${ Mn }^{ + },\quad { Fe }^{ 2+ },\quad Cr$

Show answer
Correct Option: C

The law of  traids is not applicable on

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

  1. $Cl, Br,I$

  2. $Na, K, Rb$

  3. $S, Se, Te$

  4. $Ca, Sr, Ba$

Show answer
Correct Option: B

The law of traids is applicable to :

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

  1. $C, N, O$

  2. $H, O, N$

  3. $Na, K, Rb$

  4. $Cl, Br, I$

Show answer
Correct Option: D

In the Doberiener's triad, all three elements have similar:

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

  1. electronic configuration

  2. properties

  3. number of shells

  4. both A and B

Show answer
Correct Option: B
Explanation:

In the Doberiener's triad, all three elements have similar properties and the atomic weight of the middle member of each triad is very close to the arithmetic mean (average) of the other two elements.


The Dobereiner's triads include (1) Li, Na, K (2) Ca, Sr, Ba and (3) Cl, Br, I.

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

The law of triads is not applicable to :

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

  1. $Os, Ir, Pt$

  2. $Ca, Sr, Ba$

  3. $Fe, Co, Ni$

  4. $Ru, Rh, Pt$

Show answer
Correct Option: C,D
Explanation:

The law of triads does not apply to $Ru, Rh, Pt$.


According to the law of triads, the atomic weight of the middle element is approximately equal to the arithmetic mean of the other two elements.

The atomic weights of $Ru, Rh$ and $Pt$ are $101, 102.9$ and $195$ respectively.

The arithmetic mean of the atomic weights of $Ru$ and $Pt$ is $\displaystyle \dfrac {101+195}{2} = 148$
Hence, the atomic weight of $Rh$ is not equal to the arithmetic mean of the atomic weights of $Ru$ and $Pt$.

$Fe = 56, Co = 59$ and $Ni = 59$

Mean of the weights of $Fe$ and $N$i is not equal to the weight of $Co$.


Hence, the correct options are $\text{C}$ and $\text{D}$

Atomic wt. of P is 31 and Sb is 120. What will be the atomic wt. of As, as per Dobernier triad rule?

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

  1. $151$

  2. $75.5$

  3. $89.5$

  4. Unpredictable

Show answer
Correct Option: B
Explanation:

Atomic wt. of P is 31 and Sb is 120. The atomic wt. of As, as per Dobernier triad rule will be average of two. It will be $\displaystyle \frac {31+120}{2} = \frac {151}{2} =75.5 $

Atomic wt. of $Cl = 35.5$ and of $I = 127$. According to Doeberiner triad rule atomic wt. of $Br$ will be:

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

  1. $80.0$

  2. $162.5$

  3. $81.25$

  4. $91.5$

Show answer
Correct Option: C
Explanation:

Atomic wt. of Cl = 35.5 and I = 127.


According to Doberiner triad rule:

Br =$\dfrac {35.5 +127}{2}=\dfrac {162.5}{2}=81.25$

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