Tag: dobereiner's triads

Questions Related to dobereiner's triads

In Doberenier triads, the atomic weights of the elements in a triad are in increasing order.
State whether the given statement is true or false.

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

  1. True

  2. False

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Correct Option: A
Explanation:

In 1829, Dobereiner proposed the Law of Triads: Middle element in the triad had the atomic weight that was the average of the other two members. Soon other scientists found chemical relationships extended beyond triads. Fluorine was added to Cl/Br/I group; sulfur, oxygen, selenium, and tellurium were grouped into a family; nitrogen, phosphorus, arsenic, antimony, and bismuth were classified as another group. In a group, those were in increasing order of atomic weight. Hence, the statement is true.

When a Dobereiner's triad is considered, the sum of atomic weights of the terminal elements $X$ and $Z$ is 162.5. The atomic weight of $Z$ is 50 units less than 5 times that of $X$. Identify the periods of $X, Y$ and $Z$ respectively in the present periodic table.

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

  1. $3,4,5$

  2. $4,5,6$

  3. $2,3,4$

  4. $3,5,4$

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Correct Option: A
Explanation:

Let the atomic weights (in g/mol) of elements X, Y and Z be x, y and z respectively.
The atomic weight of Z is 50 units less than 5 times that of X.

$\displaystyle z = 5x-50$.....(1)

The sum of atomic weights of the terminal elements X and Z is 162.5
$\displaystyle x+z=162.5$
$\displaystyle z = 162.5-x$......(2)

Substitute (2) into (1)
$\displaystyle 162.5-x=5x-50$
$\displaystyle 162.5=6x-50$
$\displaystyle 6x=212.5$
$\displaystyle x=35.4$ g/mol

Substitute this in equation (2)
$\displaystyle z = 162.5-x = 162.5-35.4=127.1$ g/mol.

The atomic weight of Y is the arithmetic mean of the atomic weights of X and Z.
$\displaystyle y = \dfrac {x+z}{2}$
$\displaystyle y = \dfrac {35.4+127.1}{2}=81.3$ g/mol.

From the periodic table, we see that the elements with atomic weights 35.4, 81.3 and 127.1 belong to 3 (chlorine), 4 (bromine) and 5 (iodine).

Hence, the option (A) is the correct answer.

The early attempts to classify elements were based on:

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

  1. Atomic number

  2. Atomic mass

  3. Electronic configuration

  4. None,of these

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Correct Option: B
Explanation:

In the periodic table of 1860 elements were arranged on the basis of their atomic weight properties. Elements with same chemical properties have nearly same atomic weight values.

Which of the following statements are true?

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

  1. All the trans-uranic elements are synthetic elements

  2. Elements of third group are called bridge elements

  3. Element of $1 s^2$ configuration is placed in IIA group

  4. Electronic configuration of elements of a group is same

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Correct Option: A,B

Which is mismatched regarding the position of the elements as given below?

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

  1. X(Y=89), f - block, 6th period

  2. Y(Z=100), f - block, 7th period

  3. Z(Z=115), d - block, 7th period

  4. Both (1) & (3)

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Correct Option: D

Electronic configuration of silver atom in ground state.

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

  1. $\left[ Kr \right] { 3d }^{ 10 }{ 4s }^{ 1 }$

  2. $\left[ Xe \right] { 4f }^{ 14 }{ 5d }^{ 10 }{ 6s }^{ 1 }$

  3. $\left[ Kr \right] { 4d }^{ 10 }{ 5s }^{ 1 }$

  4. $\left[ Kr \right] { 4d }^{ 9 }{ 5s }^{ 2 }$

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Correct Option: C
Explanation:

The electronic configuration of $Ag$ in ground state is:$[Kr]4d^{10}5s^1$

Write True or false:

The symbol of gold is Ag.

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

  1. True

  2. False

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Correct Option: B
Explanation:

Symbol for gold is Au.

So, option-B is correct.

Neptunium is named after the: 

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

  1. Planet Neptune

  2. Scientst Naptuna

  3. Place Naptunnom

  4. None of these

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Correct Option: A
Explanation:

Neptunium is named after the planet Neptune.

Tungsten is obtained from the latin name:

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

  1. Wolfram

  2. Wolfire

  3. Wolfoam

  4. Wolfox

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Correct Option: A
Explanation:

The symbol for tungsten, W, comes from tungsten's Latin name Wolfram. The Latin name is derived from the tungsten mineral wolframite.


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

Fill in the blanks 
Zero group elements are known as _________.

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

  1. chalcogen

  2. inert gases

  3. halogens

  4. alkali metals

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Correct Option: B
Explanation:

The $'0'$ group elements have complete octate in outermost shell. As a result they have stable configuration due to which, they do not react with other elements. Hence they are known as inert gases.