Periodic Classification of Elements — Previous Year Questions (Class 10 Science)
The periodic table organizes elements by their properties and atomic number. Understanding periodic trends is essential for predicting reactivity and bondi
TL;DR: The periodic table organizes elements by their properties and atomic number. Understanding periodic trends is essential for predicting reactivity and…
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The periodic table organizes elements by their properties and atomic number. Understanding periodic trends is essential for predicting reactivity and bondi
Periodic Classification of Elements — Previous Year Questions with Solutions
Q (2023, 3 marks): State Mendeleev's periodic law and explain one limitation he faced in arranging the elements.
Answer: Mendeleev's periodic law: The properties of elements are periodic functions of their atomic weights.
Limitation: Elements did not always follow the order of increasing atomic weight. For example, cobalt (atomic weight 58.9) was placed before nickel (atomic weight 58.7) because their chemical properties warranted this arrangement, contradicting strict atomic weight ordering.
Q (2022, 2 marks): State the modern periodic law and explain how it overcomes Mendeleev's limitations.
Answer: Modern periodic law: The properties of elements are periodic functions of their atomic numbers.
It overcomes Mendeleev's limitations by:
1. Using atomic number instead of atomic weight, which resolves the cobalt-nickel anomaly.
2. Providing a logical basis for the arrangement of all 118 known elements.
3. Allowing accurate prediction of element properties based on electron configuration.
Q (2023, 2 marks): What is the relationship between valency and position of an element in the periodic table?
Answer: In the periodic table:
1. Valency increases across a period from left to right (1 to 8).
2. Elements in the same group have the same valency.
3. Valency = number of valence electrons (for main group elements).
Example: Elements in Group 17 (halogens) have 7 valence electrons and show a valency of 1 (in forming compounds with metals).
Q (2022, 3 marks): Compare the properties of sodium and chlorine and explain these differences based on their positions in the periodic table.
Answer: Sodium (Na): Period 3, Group 1; Atomic number 11; Configuration: 2,8,1
Chlorine (Cl): Period 3, Group 17; Atomic number 17; Configuration: 2,8,7
Property differences:
1. Reactivity: Sodium is highly reactive (loses 1 electron easily), chlorine is moderately reactive (gains 1 electron).
2. Physical state: Sodium is a solid metal, chlorine is a gas.
3. Electronegativity: Chlorine is highly electronegative, sodium has low electronegativity.
4. Ionic/Covalent: Sodium forms ionic compounds, chlorine forms covalent compounds.
These differences arise because sodium has fewer valence electrons and loses them easily, while chlorine has many valence electrons and tends to gain more.
Q (2023, 2 marks): How do metallic and non-metallic characters vary in the periodic table?
Answer: 1. Across a period (left to right): Metallic character decreases. Metals are on the left, transition to metalloids, then non-metals on the right.
2. Down a group: Metallic character increases. As we go down, elements become more metallic.
3. The transition from metals to non-metals occurs along a zigzag line called the metalloid line.
Example: In period 3: Na (metal) → Si (metalloid) → Cl (non-metal)
Q (2021, 3 marks): What are halogens and chalcogens? Give their general properties and examples.
Answer: Halogens (Group 17):
Properties: Highly reactive non-metals, diatomic molecules (X2), form 1- anions, strong oxidizing agents.
Examples: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I).
Chalcogens (Group 16):
Properties: Non-metals, show variable valency (-2, +4, +6), form oxides and sulfides, less reactive than halogens.
Examples: Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (Te).
Frequently Asked Questions
What is the difference between a group and a period in the periodic table?
A group is a vertical column in the periodic table. Elements in the same group have similar valence electrons and show similar chemical properties. A period is a horizontal row in the periodic table. Properties change gradually across a period from left to right.
Why is hydrogen placed separately in some periodic tables?
Hydrogen is unique because it has only 1 electron and can lose or gain electrons to achieve stability. It can behave like alkali metals (Group 1) by losing an electron, or like halogens (Group 17) by gaining an electron. Therefore, its position in the periodic table is sometimes ambiguous.
More Class 10 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Acids, Bases and Salts
- Metals and Non-metals
- Life Processes
🤖 Stuck on any of these? Ask Syllab's free AI Tutor to explain step by step →