Chapter 3 Classification Of Elements And Periodicity In Properties

Question 1. Consider the isoelectronic species, Na⁺, Mg²⁺, F^– and O^2–. The correct order of increasing length of their radii is _________.

(i) F^- < O^2– < Mg²⁺ < Na⁺

(ii) Mg²⁺ < Na⁺ < F^– < O^2–

(iii) O^2– < F^– < Na⁺ < Mg²⁺

(iv) O^2– < F^– < Mg²⁺ < Na⁺

Question 2. Which of the following is not an actinoid?

(i) Curium (Z = 96)

(ii) Californium (Z = 98)

(iii) Uranium (Z = 92)

(iv) Terbium (Z = 65)

Question 3. The order of screening effect of electrons of s, p, d and f orbitals of a given shell of an atom on its outer shell electrons is:

(i) s > p > d > f

(ii) f > d > p > s

(iii) p < d < s > f

(iv) f > p > s > d

Question 4. The first ionisation enthalpies of Na, Mg, Al and Si are in the order:

(i) Na < Mg > Al < Si

(ii) Na > Mg > Al > Si

(iii) Na < Mg < Al < Si

(iv) Na > Mg > Al < Si

Question 5. The electronic configuration of gadolinium (Atomic number 64) is

(i) [Xe] 4f³ 5d⁵ 6s²

(ii) [Xe] 4f⁷ 5d² 6s¹

(iii) [Xe] 4f⁷ 5d¹ 6s²

(iv) [Xe] 4f⁸ 5d⁶ 6s²

Question 6. The statement that is not correct for periodic classification of elements is:

(i) The properties of elements are periodic function of their atomic numbers.

(ii) Non metallic elements are less in number than metallic elements.

(iii) For transition elements, the 3d-orbitals are filled with electrons after 3p-orbitals and before 4s-orbitals.

(iv) The first ionisation enthalpies of elements generally increase with increase in atomic number as we go along a period.

Question 7. Among halogens, the correct order of amount of energy released in electron gain (electron gain enthalpy) is:

(i) F > Cl > Br > I

(ii) F < Cl < Br < I

(iii) F < Cl > Br > I

(iv) F < Cl < Br < I

Question 8. The period number in the long form of the periodic table is equal to

(i) magnetic quantum number of any element of the period.

(ii) atomic number of any element of the period.

(iii) maximum Principal quantum number of any element of the period.

(iv) maximum Azimuthal quantum number of any element of the period.

Question 9. The elements in which electrons are progressively filled in 4f-orbital are called

(i) actinoids

(ii) transition elements

(iii) lanthanoids

(iv) halogens

Question 10. Which of the following is the correct order of size of the given species:

(i) I > I^– > I⁺

(ii) I⁺ > I^– > I

(iii) I > I⁺ > I^–

(iv) I^– > I > I⁺

Question 11. The formation of the oxide ion, O^2–(g), from oxygen atom requires first an exothermic and then an endothermic step as shown below:

O(g) + e^– → O^–(g); $\Delta$H = – 141 kJ mol^–1

O^–(g) + e^– → O^2–(g); $\Delta$H = + 780 kJ mol^–1

Thus process of formation of O^2– in gas phase is unfavourable even though O^2– is isoelectronic with neon. It is due to the fact that,

(i) oxygen is more electronegative.

(ii) addition of electron in oxygen results in larger size of the ion.

(iii) electron repulsion outweighs the stability gained by achieving noble gas configuration.

(iv) O^– ion has comparatively smaller size than oxygen atom.

Question 12. Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option.

In the modern periodic table, elements are arranged in order of increasing atomic numbers which is related to the electronic configuration. Depending upon the type of orbitals receiving the last electron, the elements in the periodic table have been divided into four blocks, viz, s, p, d and f. The modern periodic table consists of 7 periods and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Arfbau principle, the seven periods (1 to 7) have 2, 8, 8, 18, 18, 32 and 32 elements respectively. The seventh period is still incomplete. To avoid the periodic table being too long, the two series of f-block elements, called lanthanoids and actinoids are placed at the bottom of the main body of the periodic table.

(a) The element with atomic number 57 belongs to

(i) s-block

(ii) p-block

(iii) d-block

(iv) f-block

(b) The last element of the p-block in 6th period is represented by the outermost electronic configuration.

(i) 7s² 7p⁶

(ii) 5f¹⁴ 6d¹⁰ 7s² 7p⁰

(iii) 4f¹⁴ 5d¹⁰ 6s² 6p⁶

(iv) 4f¹⁴ 5d¹⁰ 6s² 6p⁴

(c) Which of the elements whose atomic numbers are given below, cannot be accommodated in the present set up of the long form of the periodic table?

(i) 107

(ii) 118

(iii) 126

(iv) 102

(d) The electronic configuration of the element which is just above the element with atomic number 43 in the same group is ________.

(i) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s²

(ii) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s³ 4p⁶

(iii) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²

(iv) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷ 4s²

(e) The elements with atomic numbers 35, 53 and 85 are all ________.

(i) noble gases

(ii) halogens

(iii) heavy metals

(iv) light metals

Question 13. Electronic configurations of four elements A, B, C and D are given below :

(A) 1s² 2s² 2p⁶

(B) 1s² 2s² 2p⁴

(C) 1s² 2s² 2p⁶ 3s¹

(D) 1s² 2s² 2p⁵

Which of the following is the correct order of increasing tendency to gain electron :

(i) A < C < B < D

(ii) A < B < C < D

(iii) D < B < C < A

(iv) D < A < B < C

Question 14. Which of the following elements can show covalency greater than 4?

(i) Be

(ii) P

(iii) S

(iv) B

Question 15. Those elements impart colour to the flame on heating in it, the atoms of which require low energy for the ionisation (i.e., absorb energy in the visible region of spectrum). The elements of which of the following groups will impart colour to the flame?

(i) 2

(ii) 13

(iii) 1

(iv) 17

Question 16. Which of the following sequences contain atomic numbers of only representative elements?

(i) 3, 33, 53, 87

(ii) 2, 10, 22, 36

(iii) 7, 17, 25, 37, 48

(iv) 9, 35, 51, 88

Question 17. Which of the following elements will gain one electron more readily in comparison to other elements of their group?

(i) S (g)

(ii) Na (g)

(iii) O (g)

(iv) Cl (g)

Question 18. Which of the following statements are correct?

(i) Helium has the highest first ionisation enthalpy in the periodic table.

(ii) Chlorine has less negative electron gain enthalpy than fluorine.

(iii) Mercury and bromine are liquids at room temperature.

(iv) In any period, atomic radius of alkali metal is the highest.

Question 19. Which of the following sets contain only isoelectronic ions?

(i) Zn²⁺, Ca²⁺, Ga³⁺, Al³⁺

(ii) K⁺, Ca²⁺, Sc³⁺, Cl^–

(iii) P^3–, S^2–, Cl^–, K⁺

(iv) Ti⁴⁺, Ar, Cr³⁺, V⁵⁺

Question 20. In which of the following options order of arrangement does not agree with the variation of property indicated against it?

(i) Al³⁺ < Mg²⁺ < Na⁺ < F^– (increasing ionic size)

(ii) B < C < N < O (increasing first ionisation enthalpy)

(iii) I < Br < Cl < F (increasing electron gain enthalpy)

(iv) Li < Na < K < Rb (increasing metallic radius)

Question 21. Which of the following have no unit?

(i) Electronegativity

(ii) Electron gain enthalpy

(iii) Ionisation enthalpy

(iv) Metallic character

Question 22. Ionic radii vary in

(i) inverse proportion to the effective nuclear charge.

(ii) inverse proportion to the square of effective nuclear charge.

(iii) direct proportion to the screening effect.

(iv) direct proportion to the square of screening effect.

Question 23. An element belongs to 3rd period and group-13 of the periodic table. Which of the following properties will be shown by the element?

(i) Good conductor of electricity

(ii) Liquid, metallic

(iii) Solid, metallic

(iv) Solid, non metallic

Question 24. Explain why the electron gain enthalpy of fluorine is less negative than that of chlorine.

Question 25. All transition elements are d-block elements, but all d-block elements are not transition elements. Explain.

Question 26. Identify the group and valency of the element having atomic number 119. Also predict the outermost electronic configuration and write the general formula of its oxide.

Question 27. Ionisation enthalpies of elements of second period are given below :

Ionisation enthalpy/ k cal mol^–1 : 520, 899, 801, 1086, 1402, 1314, 1681, 2080.

Match the correct enthalpy with the elements and complete the graph given in Fig. 3.1. Also write symbols of elements with their atomic number.

Question 28. Among the elements B, Al, C and Si,

(i) which element has the highest first ionisation enthalpy?

(ii) which element has the most metallic character?

Justify your answer in each case.

Question 29. Write four characteristic properties of p-block elements.

Question 30. Choose the correct order of atomic radii of fluorine and neon (in pm) out of the options given below and justify your answer.

(i) 72, 160

(ii) 160, 160

(iii) 72, 72

(iv) 160, 72

Question 31. Illustrate by taking examples of transition elements and non-transition elements that oxidation states of elements are largely based on electronic configuration.

Question 32. Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionisation enthalpy than nitrogen. Explain.

Question 33. First member of each group of representative elements (i.e., s and p-block elements) shows anomalous behaviour. Illustrate with two examples.

Question 34. p-Block elements form acidic, basic and amphoteric oxides. Explain each property by giving two examples and also write the reactions of these oxides with water.

Question 35. How would you explain the fact that first ionisation enthalpy of sodium is lower than that of magnesium but its second ionisation enthalpy is higher than that of magnesium?

Question 36. What do you understand by exothermic reaction and endothermic reaction? Give one example of each type.

Question 37. Arrange the elements N, P, O and S in the order of-

(i) increasing first ionisation enthalpy.

(ii) increasing non metallic character.

Give reason for the arrangement assigned.

Question 38. Explain the deviation in ionisation enthalpy of some elements from the general trend by using Fig. 3.2.

Question 39. Explain the following:

(a) Electronegativity of elements increase on moving from left to right in the periodic table.

(b) Ionisation enthalpy decrease in a group from top to bottom?

Question 40. How does the metallic and non metallic character vary on moving from left to right in a period?

Question 41. The radius of Na⁺ cation is less than that of Na atom. Give reason.

Question 42. Among alkali metals which element do you expect to be least electronegative and why?

Question 43. Match the correct atomic radius with the element.

Element

Be

C

O

B

N

Atomic radius (pm)

74

88

111

77

66

Question 44. Match the correct ionisation enthalpies and electron gain enthalpies of the following elements.

Elements

(i) Most reactive non metal

(ii) Most reactive metal

(iii) Least reactive element

(iv) Metal forming binary halide

$\Delta$H₁

A. 419

B. 1681

C. 738

D. 2372

$\Delta$H₂

3051

3374

1451

5251

$\Delta$_egH

– 48

– 328

– 40

+ 48

Question 45. Electronic configuration of some elements is given in Column I and their electron gain enthalpies are given in Column II. Match the electronic configuration with electron gain enthalpy.

Column (I)

Electronic configuration

(i) 1s² 2s² 2p⁶

(ii) 1s² 2s² 2p⁶ 3s¹

(iii) 1s² 2s² 2p⁵

(iv) 1s² 2s² 2p⁴

Column (II)

Electron gain enthalpy/kJ mol^–1

(A) – 53

(B) – 328

(C) – 141

(D) + 48

Question 46. Assertion (A) : Generally, ionisation enthalpy increases from left to right in a period.

Reason (R) : When successive electrons are added to the orbitals in the same principal quantum level, the shielding effect of inner core of electrons does not increase very much to compensate for the increased attraction of the electron to the nucleus.

(i) Assertion is correct statement and reason is wrong statement.

(ii) Assertion and reason both are correct statements and reason is correct explanation of assertion.

(iii) Assertion and reason both are wrong statements.

(iv) Assertion is wrong statement and reason is correct statement.

Question 47. Assertion (A) : Boron has a smaller first ionisation enthalpy than beryllium.

Reason (R) : The penetration of a 2s electron to the nucleus is more than the 2p electron hence 2p electron is more shielded by the inner core of electrons than the 2s electrons.

(i) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

(ii) Assertion is correct statement but reason is wrong statement.

(iii) Assertion and reason both are correct statements and reason is correct explanation for assertion.

(iv) Assertion and reason both are wrong statements.

Question 48. Assertion (A) : Electron gain enthalpy becomes less negative as we go down a group.

Reason (R) : Size of the atom increases on going down the group and the added electron would be farther from the nucleus.

(i) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

(ii) Assertion and reason both are correct statements and reason is correct explanation for assertion.

(iii) Assertion and reason both are wrong statements.

(iv) Assertion is wrong statement but reason is correct statement.

Question 49. Discuss the factors affecting electron gain enthalpy and the trend in its variation in the periodic table.

Question 50. Define ionisation enthalpy. Discuss the factors affecting ionisation enthalpy of the elements and its trends in the periodic table.

Question 51. Justify the given statement with suitable examples— “the Properties of the elements are a periodic function of their atomic numbers”.

Question 52. Write down the outermost electronic configuration of alkali metals. How will you justify their placement in group 1 of the periodic table?

Question 53. Write the drawbacks in Mendeleev’s periodic table that led to its modification.

Question 54. In what manner is the long form of periodic table better than Mendeleev’s periodic table? Explain with examples.

Question 55. Discuss and compare the trend in ionisation enthalpy of the elements of group1 with those of group17 elements.