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 atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

If $N _A$ is the Avogadro's number then number of valence electrons in 4.8 g of $O^{2-} $ is:

  1. $2.4\, N _A$
  2. $4.2\, N _A$
  3. $1.6\, N _A$
  4. $3.2\, N _A$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Number of mole in 4.8 gm of oxygen atom $=\dfrac{4.8}{16} = 0.3$ mole 

Number of the valence electron in one ion of $O^{2-} = 8$

Number of the valence electron in 0.3 mole of $O^{2-} = 8\times0.3\times N _A =2.4N _A$

Hence, the correct option is $(A)$.
Multiple choice chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

According to the law of triads :

  1. the properties of the middle element were in between those of the other two members.

  2. three elements arranged according to increasing weights have similar properties.

  3. the elements can be grouped in the groups of six elements.

  4. every third element resembles the first element in periodic table.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Dobereiner's law of triads, the properties of the middle element were in between those of the other two members. The elements were arranged in a group of three (called triads). The atomic weight of a middle element was almost the average of the other two. Three elements of the triad had similar chemical properties.

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

The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. Such an arrangement of elements called as :

  1. Dobereiner triad.

  2. Mendeleev triad.

  3. Modern triad.

  4. none of the above.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Dobereiner observed in few atoms that mass of one atom is equal to the average of two atoms. He defined almost all properties basing on atomic weight.Later on it was proved wrong any-ways. Hence, this is called Dobereiner triad. Lithium has 7, sodium has 23 where as potassium has 39 as atomic masses.
$ 23 = (7+39)/2 = 23$

Here, we could observe that sodium atomic mass is average of potassium and lithium masses. 

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

If the two members of a Dobereiner triad are phosphorus and antimony, the third member of this triad is :

  1. arsenic

  2. sulphur

  3. iodine

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

According to Dobereiner, the atomic mass of the middle element was nearly equal to the arithmetic mean of the other two. Therefore, the atomic mass of the third element is $=$ $\frac{{31}+{121.75}}{2}$ $=$ 76.37 which is nearly equal to the atomic mass of arsenic.

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 Dobereiner's triad?

  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 atomic mass of the middle element should be the average of the atomic masses of the first and third elements. In case of C and D options, the atomic masses do not correspond to that rule.

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

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 $\text{B}$