Master the fundamentals of periodic table trends and reactions with this detailed guide. Explore key concepts, including ionization energy, electron affinity, and metallic vs. non-metallic character. Learn how sodium and magnesium react with oxygen, chlorine, and water, and uncover the variations in the nature of oxides across Period 3. Understand the significance of atomic radii trends, the amphoteric behavior of Al2O3, and the classification of s- and p-block elements. Dive into practical examples and explanations to simplify your study of chemistry and ace your exams!
Multiple Choice Questions (MCQs)
(i) Correct answer: (d) principal quantum number
Explanation: The period number corresponds to the principal quantum number (( n )) of the outermost shell of electrons.
(ii) Correct answer: (a) F
Explanation: Fluorine has the highest electronegativity due to its small size and high effective nuclear charge.
(iii) Correct answer: (a) Na2O
Explanation: Na2O is a basic oxide and produces a base (NaOH) when dissolved in water.
(iv) Correct answer: (d) alkaline earth metal
Explanation: Magnesium (Mg) belongs to Group 2A (alkaline earth metals).
(v) Correct answer: (b) group 14
Explanation: The electron configuration (1s(^2), 2s(^2), 2p(^6), 3s(^2), 3p(^2)) corresponds to silicon (Si), which is in Group 14.
(vi) Correct answer: (a) Li
Explanation: Lithium has the highest ionization energy due to its smaller size compared to the other elements in the group.
(vii) Correct answer: (d) I
Explanation: Iodine has the lowest electron affinity due to its large atomic size and lower effective nuclear charge.
(viii) Correct answer: (c) Al(_2)O(_3)
Explanation: Aluminum oxide (Al2O3) is amphoteric as it reacts with both acids and bases.
(ix) Correct answer: (d) G-VIIA
Explanation: Elements in Group VIIA (halogens) have strong non-metallic character due to their high electronegativity.
(x) Correct answer: (a) B
Explanation: Boron has the smallest ionization energy among the given options because of its lower nuclear charge compared to other elements.
Short Answer Questions
(i) What is a period?
A period is a horizontal row in the periodic table. Elements in the same period have the same number of electron shells.
(ii) Differentiate between s-block and p-block elements.
- s-block elements: These elements have their outermost electrons in the s-orbital (Groups 1 and 2).
- p-block elements: These elements have their outermost electrons in the p-orbital (Groups 13 to 18).
(iii) Position of sulfur (atomic number 16) in the periodic table:
- Electron configuration: 1s(^2), 2s(^2), 2p(^6), 3s(^2), 3p(^4).
- Period: 3 (3 electron shells), Group: 16 (6 valence electrons).
(iv) Position of element with configuration 1s(^2), 2s(^2), 2p(^6), 3s(^2), 3p(^3):
- Electron configuration corresponds to phosphorus (P).
- Period: 3, Group: 15 (5 valence electrons).
(v) How do metals differ from metalloids?
- Metals are good conductors of heat and electricity, malleable, ductile, and have metallic luster.
- Metalloids have properties intermediate between metals and non-metals (e.g., semiconductors like silicon).
(vi) Why is a cation smaller than its atom?
A cation forms when an atom loses one or more electrons, resulting in decreased electron-electron repulsion and a stronger attraction of the remaining electrons toward the nucleus.
Descriptive Questions
1. Describe the reactions of sodium and magnesium with:
(i) Oxygen:
- Sodium reacts to form sodium oxide (Na2O).
- Magnesium reacts to form magnesium oxide (MgO).
(ii) Chlorine:
- Sodium forms sodium chloride (NaCl).
- Magnesium forms magnesium chloride (MgCl2).
(iii) Water:
- Sodium reacts vigorously with water to form sodium hydroxide (NaOH) and hydrogen gas.
- Magnesium reacts slowly with water at room temperature but more rapidly with steam to form MgO and hydrogen gas.
2. Variation in nature of oxides of Period 3 elements:
- Oxides vary from basic (e.g., Na2O) to amphoteric (e.g., Al2O3) to acidic (e.g., SO3).
3. Variation in metallic and non-metallic character in the periodic table:
- Metallic character increases down a group and decreases across a period.
- Non-metallic character decreases down a group and increases across a period.
4. Why do atomic radii decrease across a period?
As you move across a period, the number of protons increases, resulting in a greater nuclear charge, which pulls electrons closer to the nucleus.
5. Why do atomic radii increase down a group?
As you move down a group, additional electron shells are added, increasing the distance between the nucleus and the outermost electrons.
6. How does the periodic table help in understanding the properties of elements?
The periodic table organizes elements based on their atomic structure, allowing predictions of their chemical and physical properties (e.g., reactivity, electronegativity, and ionization energy).
7. Significance of the periodic table:
- Systematic classification of elements.
- Predicts element properties and trends.
- Helps in understanding the chemical behavior and bonding of elements.
8. Periodic table and oxide characteristics across periods:
- Moving left to right, oxides change from basic (Na2O, MgO) to amphoteric (Al2O3) to acidic (SO3), P2O5).
