Chemistry

Periodic Classification and Elements

1,092 Questions

Periodic classification organizes chemical elements based on atomic structure, periodic laws, and elemental properties. It covers historical classification systems, electron configurations, and periodic trends. Test takers preparing for chemistry sections will find these questions crucial for mastering fundamental element properties and atomic interactions.

Periodic table structureAtomic orbitalsElement identificationPeriodic laws

Periodic Classification and Elements Questions

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 $

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

If three elements X, Y, and Z form a Dobereiner's triad and atomic weights of X and Z are 9 and 40 respectively, then the atomic weight of the element Y is approximately:

  1. 24.5

  2. 49

  3. 34.5

  4. 29
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Dobereiner, the atomic weight of the central element of the triad is the arithmetic mean of the atomic weights of the other two members. 


Therefore, atomic weight of Y = $\cfrac{9 + 40}{2} = 24.5\ g$


Hence, option A is correct.

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

Law of Triad was proposed by:

  1. Newland

  2. Gay Lussac

  3. Mendeleev

  4. Dobereiner
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Dobereiner, in 1817 suggested a relationship between the properties of elements and their atomic weights. According to Dobereiner, the atomic weight of the middle element is nearly the same as average of the atomic weights of other two elements.

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

Three elements X, Y and Z form a Dobereiner triad. The ratio of the atomic weight of X to that of Z is 7: 25.


 If the sum of the atomic weights of X and Z is 160, find the atomic weights of X, Y and Z.

  1. X $\rightarrow$ 35, Y $\rightarrow$ 80, Z $\rightarrow$ 125
  2. X $\rightarrow$ 125, Y $\rightarrow$ 80, Z $\rightarrow$ 35
  3. X $\rightarrow$ 80, Y $\rightarrow$ 35, Z $\rightarrow$ 125
  4. X $\rightarrow$ 80, Y $\rightarrow$ 125, Z $\rightarrow$ 35
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Let weight of X be $7a$  $\therefore$ Atomic weight of $Z=25a$

$\therefore7a+25a=160$

$\Rightarrow a=5$

Weight of X$=35$ and of Z is $125$

Atomic weight of Y is arranged of X and $2=\cfrac { 35+125 }{ 2 } =80$

Hence, the correct option is $\text{A}$
Multiple choice chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

Which of the following sets of atomic masses do not correspond to Dobernier traid?

  1. $7, 23, 39$
  2. $20, 38, 56$
  3. $47, 91, 178$
  4. $54, 95, 183$
Reveal answer Fill a bubble to check yourself
C,D Correct answer
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} $

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

Dobereiner was the first person to illustrate the relationship between the ____________ of elements and their properties.

  1. atomic masses

  2. electron negativity

  3. molecular masses

  4. number of protons
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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:

  1. $300$
  2. $175$
  3. $125$
  4. $150$
Reveal answer Fill a bubble to check yourself
D Correct answer
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 $\text{D}$

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

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.

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

An element $X$ belongs to fourth period and fifteenth group of the periodic table. Which of the following statements is true?

  1. It has a completely filled s-orbital and a partially filled d-orbital.

  2. It has completely filled s-and p-orbitals and a partially filled d-orbital.

  3. It has completely filled s-and p-orbitals and a half-filled d-orbital.

  4. It has a half-filled p-orbital and completely filled s-and d-orbitals.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Group 15 has a valence shell electronic configuration of $ns^2np^5$ and period $=4$$ means its $n=4$

thus electronic configuration of element $X$  is $4s^24p^3$

Elements of Group 15 and period 2 onwards are: $N, P, As, Sb, Bi$

Thus $X$ is Arsenic ($As$) and has electronic configuration of: $1s^22s^22p^63s^23p^63d^{10}4s^24p^3$. 

Thus, $s$ and $d-$orbitals are fully-filled and $p-$orbital is half-filled.

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