Chemistry Class 11 NCERT Solutions: Chapter 3 Classification of Elements and Periodicity Part 5

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Q: 30. Assign the position of the element having outer electronic configuration

(i)

(ii)

(iii) In the periodic table

Answer:

(i) Since , the element belongs to the period. It is a p-block element since the last electron occupies the p-orbital.

There are four electrons in the p-orbital. Thus, the corresponding group of the element

=Number of s-block group + number of d-block groups number of p-electrons

Therefore, the element belongs to the period and group of the periodic table. Hence, the element is Sulphur.

(ii) Since , the element belongs to the period. It is a d-block element as d-orbitals are incompletely filled. There are electrons in the d-orbital.

Thus, the corresponding group of the element

= Number of s-block groups + number of d-block groups

Therefore, it is a 4th group element. Hence, the element is Titanium.

(iii) Since , the element is present in the period. It is an f –block element as the last electron occupies the f-orbital. It belongs to group 3 of the periodic table since all f-block elements belong to group 3. Its electronic configuration is thus, its atomic number is Hence, and the element is Gadolinium.

Q: 31. The first and the second ionization enthalpies and the electron gain enthalpy of a few elements are given below:

This of the above elements is likely to be:

(A) The least reactive element

(B) The most reactive metal

(C) The most reactive non-metal

(d) The least reactive non-metal

(e) The metal which can form a stable binary halide of the formula MX2, (X=halogen)

(f) The metal which can form a predominantly stable covalent halide of the formula MX (X=halogen)?

Answer:

(a) Element V is likely to be the least reactive element. This is because it has the highest first ionization enthalpy a positive electron gain enthalpy .

(b) Element ll is likely to be the most reactive element. This is because it has the highest first ionization enthalpy and a low negative electron gain enthalpy

(c) Element III is likely to be the most reactive non-metal as it has a high first ionization enthalpy and the highest negative electron gain enthalpy

(d) Element V is likely to be the least reactive non-metal since it has a very high first ionization enthalpy and a positive electron gain enthalpy

(e) Element VI has a low negative electron gain enthalpy Thus, it is a metal. Further, it has the lowest second ionization enthalpy Hence, it can form a stable binary halide of the formula

(f) Element V has the highest firs ionization energy and high second ionization energy. Therefore, it can form a predominantly stable covalent halide of the formula

Q: 32. Predict the formula of the stable binary compounds that would be formed by the combination of the following pairs of elements.

(A) Lithium and oxygen

(B) Magnesium and nitrogen

(C) Aluminium and iodine

(D) Silicon and oxygen

(E) Phosphorus and fluorine

(F) Element and fluorine

Answer:

(A) (Lithium dioxide)

(B) (Magnesium nitrite)

(C) (Aluminium triiodide)

(D) (Silicon dioxide)

(E) (Phosphorus trifluoride or pentafluoride)

(F) The element with the atomic number is Lutetium it has valency 3. Hence, the formula of the compound is (Lutetium trifluoride).

Q: 33. In the modern periodic table, the period indicates the value of:

(A) Atomic number

(B) Atomic mass

(C) Principal quantum number

(D) Azimuthal quantum number

Answer:

The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic number (number of protons in the nucleus), electron configurations, and recurring chemical properties.

The value of the principal quantum number (n) for outermost shell or the valence shell indicates a period in the Modern periodic table.