Tag: the periodic table

Questions Related to the periodic table

Cl, Br, I  follows Dobereiner's triads, the atomic masses of Cl and I are 35.5 and 127 respectively. The atomic mass of Br is : 

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

  1. 162.5

  2. 91.5

  3. 81.25

  4. 45.625

Show answer
Correct Option: C
Explanation:

According to Dobereneir's triads the atomic mass of Br will be average of the atomic masses of CI & I
 $=$ $\frac{{35.5}+{127}}{2}$ $=$ 81.25

Which of the following sets of atomic masses do not correspond to Dobereiner's triad?

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 atomic mass of the middle element should be the average of the atomic masses of the first and third elements. In case of C and D options, the atomic masses do not correspond to that rule.

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 $\text{D}$