S-Block Elements Revision Q&A

 

S-Block Elements (Alkali and Alkaline Earth Metals) Revision Q&A

1. Why are alkali metals highly reactive?

Due to their low ionization energy and tendency to lose their single valence electron to form M+ ions easily.

2. What is the general electronic configuration of alkali metals?

ns¹ where n = 1 to 7 for Li to Cs.

3. Why is lithium different from other alkali metals?

Lithium shows anomalous behavior due to its small size, high ionization enthalpy, and high polarizing power.

4. Describe the trend in atomic and ionic radii in alkali metals.

Both atomic and ionic radii increase down the group from Li to Cs.

5. How do alkali metals react with water? Write a general reaction.

Alkali metals react vigorously with water to form hydroxides and hydrogen gas: 2M + 2H₂O → 2MOH + H₂.

6. What type of oxides do alkali metals form?

Alkali metals form peroxides (e.g., Na₂O₂), superoxides (e.g., KO₂), and normal oxides (Li₂O).

7. Which alkali metal forms superoxides and why?

Potassium, rubidium, and cesium form superoxides due to their larger size and ability to stabilize the large superoxide ion.

8. Why do alkali metals readily lose their outermost electron?

Because of their low ionization enthalpy, making it easy to form stable cations in reactions.

9. How do alkali metals react with halogens?

They form ionic halides (MX) where M is the metal and X is the halogen.

10. What is the reducing nature of alkali metals?

Alkali metals are strong reducing agents due to their readiness to lose electrons.

11. What are the common uses of sodium?

Sodium is used in the synthesis of organic compounds, sodium vapor lamps, and as a reducing agent.

12. Why is beryllium different from other alkaline earth metals?

Due to its small size, high ionization enthalpy, and covalent bonding characteristics.

13. What is the general electronic configuration of alkaline earth metals?

ns², where n = 2 to 7 for Be to Ra.

14. Write the reaction of calcium with water.

Calcium reacts with water slowly to form calcium hydroxide and hydrogen gas: Ca + 2H₂O → Ca(OH)₂ + H₂.

15. Compare the reactivity of alkali metals and alkaline earth metals with water.

Alkali metals react more vigorously with water than alkaline earth metals.

16. Which alkaline earth metal is the most reactive?

Barium is the most reactive among alkaline earth metals.

17. Describe the trend in ionization energy in alkaline earth metals.

Ionization energy decreases down the group from Be to Ra.

18. What are the common oxides of alkaline earth metals?

Oxides such as BeO, MgO, CaO, SrO, BaO.

19. What happens when sodium carbonate is heated strongly?

It decomposes to sodium oxide and carbon dioxide: Na₂CO₃ → Na₂O + CO₂ (on heating).

20. Give the uses of calcium hydroxide.

Used in construction (plaster), water treatment, and as a neutralizing agent.

21. Why do alkali metals have low melting points?

Due to their large atomic size leading to weak metallic bonds.

22. What type of hydroxides do alkali metals form?

Strong alkaline hydroxides, e.g., NaOH, KOH.

23. Which alkali metal exhibits diagonal relationship with magnesium?

Lithium exhibits diagonal relationship with magnesium.

24. Why is lithium carbonate insoluble in water?

Due to the high lattice enthalpy and covalent character of lithium carbonate.

25. Write the reaction of sodium metal with liquid ammonia.

Sodium dissolves in liquid ammonia to give a blue solution containing solvated electrons.

26. How do alkaline earth metals react with acids?

They form salts and hydrogen gas: M + 2HCl → MCl₂ + H₂.

27. What is the trend in solubility of alkaline earth metal hydroxides?

Solubility increases down the group from Be to Ba.

28. Which alkaline earth metal hydroxide is least soluble in water?

Beryllium hydroxide is least soluble in water.

29. What type of halides do alkali metals form?

Ionic halides with high melting points.

30. Why are alkali metals stored under kerosene?

To prevent their reaction with moisture and oxygen in air.

31. What is the effect of hydration on the size of alkali metal ions?

Hydration increases the effective ionic radius due to water molecules attached.

32. Describe the thermal stability trend of alkaline earth metal carbonates.

Thermal stability increases down the group.

33. What is the nature of bonding in beryllium chloride?

Covalent bonding due to small size and high polarizing power of Be²⁺.

34. Give a characteristic property of alkali metal halides.

High melting and boiling points due to strong ionic bonds.

35. Why does lithium form more covalent compounds compared to other alkali metals?

Due to its small size and high polarizing power.

36. What is "diagonal relationship" in the context of s-block elements?

Similarity in properties of diagonally adjacent elements in the periodic table, e.g., Li and Mg.

37. Write the reaction of calcium carbonate upon heating.

Calcium carbonate decomposes to calcium oxide and carbon dioxide: CaCO₃ → CaO + CO₂ (with heat).

38. What is the role of calcium oxide in the steel industry?

Used as a flux to remove impurities.

39. Describe the solubility trend of alkaline earth metal sulfates.

Solubility decreases down the group.

40. Why is magnesium less reactive than calcium?

Due to higher ionization energy and stronger metallic bonding in magnesium.

41. What is the anomalous behavior of beryllium in the group 2 elements?

Beryllium shows high ionization energy, small size, and more covalent character in its compounds compared to other group 2 elements.

42. How does ionization energy change in alkali metals down the group?

Ionization energy decreases down the group from Li to Cs due to increasing atomic size.

43. What type of oxides does calcium form?

Calcium forms basic oxides such as calcium oxide (CaO).

44. What is the effect of hydration on the atomic size of alkaline earth metals?

Hydration increases the effective size due to water molecules surrounding the ion.

45. Why do alkali metals have a strong reducing nature?

Due to their low ionization enthalpy and easy loss of the outermost electron.

46. What happens when sodium reacts with chlorine gas?

Sodium reacts vigorously with chlorine to form sodium chloride (NaCl).

47. What is the general trend in electronegativity in alkali metals?

Electronegativity decreases down the group.

48. Why is beryllium hydroxide amphoteric?

Because it can react with both acids and bases forming salts and complexes respectively.

49. Explain the solubility of alkali metal salts in water.

Alkali metal salts are generally highly soluble in water due to ionic bonding.

50. What is the use of sodium bicarbonate?

Used as an antacid, in baking, and for fire extinguishers.

51. How does the reactivity of alkali metals differ in air?

Lithium forms a nitride, while other alkali metals form oxides or peroxides on exposure to air.

52. Write the reaction of magnesium with steam.

Mg + H₂O (steam) → MgO + H₂.

53. Why is calcium used in the extraction of metals?

It is a strong reducing agent and can reduce metal oxides.

54. Discuss the thermal stability of alkaline earth metal nitrates.

Stability increases down the group; lighter ones decompose to oxides and nitrogen dioxide, heavier ones form nitrites.

55. Why do alkali metals exhibit low density?

Because of their large atomic size and weak metallic bonding.

56. What is the reaction of sodium with oxygen at room temperature?

Sodium forms sodium peroxide Na₂O₂.

57. What is the characteristic flame color of sodium?

Bright yellow flame.

58. Which alkali metal is used in photoelectric cells?

Cesium.

59. How do alkaline earth metals react with nitrogen?

Some, like calcium and magnesium, form nitrides upon heating.

60. Why is magnesium used in the synthesis of Grignard reagents?

Its moderate reactivity and ability to form organomagnesium compounds make it suitable.

61. What is the nature of bonding in alkaline earth metal halides?

Mostly ionic, but Be halides have covalent character.

62. Why does beryllium chloride have a low melting point compared to other group 2 halides?

Due to its covalent molecular structure.

63. What causes the increase in ionization energy from sodium to magnesium?

Higher nuclear charge and effective nuclear charge in magnesium.

64. Write the reaction of calcium hydroxide with carbon dioxide.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.

65. What is the use of lime (CaO)?

Used in cement, steel making, and to neutralize acidic soils.

66. What is the diagonal relationship between beryllium and aluminum?

Similarities in chemical behavior due to similar charge density and covalent character.

67. What is the product formed when sodium reacts with dry chlorine gas?

Sodium chloride (NaCl).

68. Describe the solubility of calcium sulfate in water.

Moderately soluble with low solubility compared to other calcium salts.

69. What happens when alkali metals react with acids?

They form the corresponding salt and hydrogen gas.

70. Which alkali metal has the highest melting point?

Lithium.

71. Why does lithium form covalent compounds despite being a metal?

Due to its small ionic size and high polarizing power.

72. Give the commercial use of sodium hydroxide.

Used in the manufacture of soap, paper, and detergents.

73. How is calcium carbonate naturally found?

As limestone, chalk, and marble.

74. What is the role of sodium hydroxide in the Bayer process?

It is used to extract alumina from bauxite ore.

75. What is the nature of oxides formed by alkaline earth metals?

Basic oxides.

76. Why do alkaline earth metals have higher melting points compared to alkali metals?

Due to their smaller size and higher charge leading to stronger metallic bonding.

77. Explain why sodium metal cannot be stored in air.

It reacts rapidly with moisture and oxygen, forming oxides and hydroxides.

78. What is the reducing agent in metal displacement reactions among s-block metals?

The alkali metals due to their readiness to lose electrons.

79. Write the reaction of sodium carbonate with hydrochloric acid.

Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O.

80. What is the application of calcium sulfate?

Used in plaster of Paris and as a building material.

81. What is the electronic configuration of potassium?

[Ar] 4s¹.

82. How does the atomic radius change from Be to Ba?

Atomic radius increases down the group.

83. What is the characteristic reaction of alkali metals with oxygen?

Formation of oxides, peroxides, or superoxides depending on the metal.

84. Why does beryllium have a higher melting point compared to other group 2 metals?

Due to strong covalent bonding and small atomic size.

85. Write the reaction for the formation of sodium hydroxide from sodium metal.

2Na + 2H₂O → 2NaOH + H₂.

86. What is the flame color of calcium in flame tests?

Brick red.

87. Why is lithium ion smaller than sodium ion?

Because lithium has fewer electron shells and higher effective nuclear charge.

88. Which group 1 metal is most reactive?

Francium, but practically cesium is the most reactive stable element.

89. How is sodium metal prepared commercially?

By the electrolysis of molten sodium chloride.

90. What product forms when calcium reacts with nitrogen?

Calcium nitride Ca₃N₂.

91. Define the diagonal relationship with an example.

Similarity in properties of two elements diagonally positioned in the periodic table like Li and Mg.

92. Mention the use of sodium bicarbonate in medicine.

Used as an antacid to relieve acidity.

93. How does the solubility of alkali metal hydroxides change down the group?

Solubility increases from LiOH to CsOH.

94. Why does beryllium have a higher ionization energy compared to magnesium?

Because of smaller size and stronger attraction for electrons.

95. What gases are released when calcium carbonate reacts with acids?

Carbon dioxide gas is released.

96. Write the uses of sodium chloride.

Used as common salt in food, in chemical industries, and for de-icing.

97. What happens when calcium hydroxide reacts with excess CO₂?

It forms calcium bicarbonate which is soluble in water.

98. State a common property of Group 1 and Group 2 metal oxides.

Most are basic in nature.

99. Why is potassium more reactive than sodium?

Because its valence electron is farther from the nucleus and more easily lost.

100. What is the reaction of sodium with hydrogen?

Sodium hydride is formed: 2Na + H₂ → 2NaH.

101. Why is beryllium chloride covalent while other group 2 chlorides are ionic?

Due to the small size and high polarizing power of Be²⁺ ion.

102. Give a reason why calcium is used in the extraction of uranium and thorium.

It acts as a strong reducing agent for these metals.

103. What is the trend in the metallic character of alkaline earth metals?

Metallic character increases down the group.

104. How is alkali metal ion size affected by hydration?

Hydrated ion size is larger due to water molecules attached.

105. What is the nature of bonding in sodium hydroxide?

Ionic bonding with polar covalent nature in metal hydroxides.

106. Which alkali metal exhibits the greatest tendency to form organometallic compounds?

Lithium.

107. Why is calcium hydroxide called slaked lime?

Because it is produced by adding water to quicklime (CaO).

108. Write the reaction for the preparation of calcium oxide from calcium carbonate.

CaCO₃ → CaO + CO₂ (on heating).

109. What happens when sodium hydroxide is added to aqueous sodium chloride?

No reaction; the solution remains neutral.

110. Mention one use of sodium peroxide.

Used as a bleaching agent and oxygen source.