Periodic Classification of Elements in Modern Periodic Table

Periodic Classification of Elements in Modern Periodic Table

Question 1. Are Dobereiner's triads also found in the column of octaves of Newlands? Find out by comparing.
answer:- Yes, the Dobereiner's sacrum is also found in the column of octaves of Newlands. For example- Li, Na, K are Dobereiner's triplet. But they are also present in the second column of Newlands' octave.

Question 2. What are the limitations of classification of Dobereiner?
answer:- The following are the limitations of Dobereiner's classification.

All the elements known at that time could not be classified by Dobreiner's triad.
He was able to make only three of the 64 elements known at that time. Hence their classification was not very successful.

Question 3. What are the limitations of Newlands' law of octaves?
Answer: —Signs — Important facts and definitions ”.

Question 4. In addition to gallium, what elements have been detected so far, for which Mendeleeff left a blank in his periodic table? Give two examples.

Answer: In addition to gallium, scandium and germanium elements were later discovered for which a blank space was left.

Question 5. What criteria did Mendeleeff adopt to prepare his periodic table?
Answer: - Mendeleev adopted the following criteria to prepare his periodic table-

Arranged the elements in ascending order (increasing order) of atomic masses.
Arranged on the basis of similarity of chemical properties.
The formula of hydride and oxide formed from element was considered to be the fundamental property for classification of elements.

Question 6. Why do you think the noble gases are kept in a separate group?
Answer: - Excellent gases are kept in a separate group, because they are chemically inert. The outermost shells of all noble gases are completely filled and there are similarities in their properties.

Question 7. How are the various anomalies of Mendeleev's periodic table removed by the modern periodic table?

Answer: - The three discrepancies of Mendeleev's periodic table by the modern periodic table were removed in the following ways.

(i) Placement of Hydrogen - Hydrogen was topped Group 1 on the basis of similarity in properties with alkaline metals, but this was not an appropriate place. This was a shortcoming of Mendeleev's periodic table. But due to the electronic configuration being similar to alkali metal and having valence electron 1, the modern periodic table
In this, it was placed in group 1. That removed Mendeleev's first shortcoming of the periodic table.

(ii) The location of cobalt (Co) and nickel (Ni) - atomic mass of Co is 58.9 and atomic mass of Ni is 58.7; But Co was placed before Ni. But Co has atomic number 27 and Ni has atomic number 28. In the modern periodic table the elements were arranged on the basis of increasing atomic number, which also removed this deficiency. Co came in Group-9 and Ni Group-10. Similarly, the wrong order of Ar (atomic number 18) and K (atomic number 19) were also resolved.

(iii) Location of isotopes - Isotopes had no place in Mendeleev's periodic table. Since isotopes have the same atomic number. Hence, they were kept in one place in the modern periodic table. For example, the atomic numbers of Cl-35 and Cl-37 are 17.

Question 8. Write the names of two elements showing chemical reactivity like magnesium. What is the basis of your selection?

Answer: - Beryllium (Be) and calcium (Ca) will exhibit chemical reactions opposite to magnesium. The basis of our selection is-

4Be - 2, 2 and 20Ca: 2, 8, 8, 2
Their valence electrons are similar. Hence these are elements of the same class-2, which contains Mg. And will display the same quality.

Question 9. Name it.
(a) Three elements with one electron present in their outermost shell.
(b) Two elements with two electrons in their outermost shells. |
(c) Three elements whose outer shell is complete.
answer

Question 10. (a) Lithium, sodium, potassium, all these metals react with water and release hydrogen gas. Is there any similarity between the atoms of these elements?
(b) Helium is an inert gas, while the reactivity of neon is extremely low. Is there any similarity between their atoms?
answer
(a) Yes, atoms of these elements have similarity. Li, Na, and K have 1 electron in their outer shell and have the same electronic configuration. Li: 2, 1,; Na: 2, 8, 1 and K: 2, 8, 8, 1. Therefore, all these elements can easily give up 1 electron and make cations.

(b) Yes, the outer shells of both are completely filled. He: 2, Ne: 2,8 Helium has only a K cell, which can have a maximum of 2 electrons, while the outer shell (L-shell) of a neon can have a maximum of 8 electrons. Hence these are inert gases.