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Questions Related to chemistry

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 $\text{D}$

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

Show answer
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. $3,5,4$

Show answer
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

Show answer
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

Show answer
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)

Show answer
Correct Option: D