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

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

(i) Equation

(ii) Equation

(iii) Equation In the periodic table

Answer:

(i) Since Equation , the element belongs to the Equation 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 Equation number of p-electrons

Equation

Equation

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

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

Thus, the corresponding group of the element

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

Equation

Equation

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

(iii) Since Equation , the element is present in the Equation 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 Equation thus, its atomic number is Equation Hence, and the element is Gadolinium.

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

Equation

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 Equation a positive electron gain enthalpy Equation .

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

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

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

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

(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 Equation

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 Equation and fluorine

Answer:

(A) Equation (Lithium dioxide)

(B) Equation (Magnesium nitrite)

(C) Equation (Aluminium triiodide)

(D) Equation (Silicon dioxide)

(E) Equation (Phosphorus trifluoride or pentafluoride)

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

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