Tag: development of the modern periodic table

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

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

  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 = $85$
Reveal answer Fill a bubble to check yourself
A Correct answer
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 ) 

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

Following triads have approximately equal size

  1. ${ Na }^{ + },\quad { Mg }^{ 2+ },\quad { Al }^{ 3+ }$
  2. ${ F }^{ - },\quad Ne,\quad { O }^{ 2- }$
  3. $Fe,\quad Co,\quad Ni$
  4. ${ Mn }^{ + },\quad { Fe }^{ 2+ },\quad Cr$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Fe, Co, and Ni are transition metals located in the same period (Period 4) and have very similar atomic radii, making them a triad of approximately equal size.

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

The law of  traids is not applicable on

  1. $Cl, Br,I$
  2. $Na, K, Rb$
  3. $S, Se, Te$
  4. $Ca, Sr, Ba$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Dobereiner's Law of Triads states that the atomic weight of the middle element is approximately the average of the other two. Na, K, and Rb do not fit this pattern because Rb is significantly heavier than the average of Na and K.

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

The law of traids is applicable to :

  1. $C, N, O$
  2. $H, O, N$
  3. $Na, K, Rb$
  4. $Cl, Br, I$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Dobereiner's triads work best for halogens like Cl, Br, I which show a clear pattern in properties and atomic weights. Groups like C, N, O or H, O, N don't form proper triads, and Na, K, Rb are alkali metals where the pattern doesn't hold well.

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

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

  1. electronic configuration

  2. properties

  3. number of shells

  4. both A and B
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $\text{B}$

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

The law of triads is not applicable to :

  1. $Os, Ir, Pt$
  2. $Ca, Sr, Ba$
  3. $Fe, Co, Ni$
  4. $Ru, Rh, Pt$
Reveal answer Fill a bubble to check yourself
C,D Correct answer
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 $\text{D}$

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

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

  1. $151$
  2. $75.5$
  3. $89.5$

  4. Unpredictable
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $