Tag: dobereiner's triads

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

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.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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.

  1. $3,4,5$
  2. $4,5,6$
  3. $2,3,4$
  4. $3,5,4$
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  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)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Element with Z=89 (Actinium) is in the f-block (or d-block depending on convention, but usually d-block start) and 7th period. Z=100 (Fermium) is f-block, 7th period. Z=115 (Moscovium) is p-block, 7th period. The question asks for the mismatch, and since multiple entries are incorrect, D is the intended answer.

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

Electronic configuration of silver atom in ground state.

  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. $\left[ Kr \right] { 4d }^{ 9 }{ 5s }^{ 2 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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

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

  1. chalcogen

  2. inert gases

  3. halogens

  4. alkali metals
Reveal answer Fill a bubble to check yourself
B Correct answer
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.