CBSE Class 10 Science Notes Chapter 5 Periodic Classification of Elements
CBSE Class 10 Science Notes
Chapter 5: Periodic Classification of Elements
History of Classification
- Dobereiner’s Triads: Elements grouped into triads based on similar properties. E.g., Li, Na, K.
- Newlands’ Law of Octaves: Properties repeat every eighth element but fail beyond calcium.
- Mendeleev’s Periodic Table: Based on atomic mass; left gaps for undiscovered elements.
Modern Periodic Table
- Based on increasing atomic number.
- Groups (1-18) & Periods (1-7).
- Metals, non-metals, and metalloids are classified separately.
Trends in the Periodic Table
- Atomic Size: Decreases across a period, increases down a group.
- Ionization Energy: Increases across a period, decreases down a group.
- Electronegativity: Increases across a period, decreases down a group.
- Metallic vs. Non-metallic Character: Metallic character decreases across a period.
Significance
- Predicts properties of elements and their compounds.
- Explains chemical reactivity trends.
Most Important Science Class 10 Questions Answers For the 2025 Board Examination
Top Most Asked Questions and Answers
Chapter 5: Periodic Classification of Elements
Why did Mendeleev leave gaps in his periodic table?
Mendeleev left gaps to accommodate undiscovered elements, predicting their properties. For example, he predicted the existence and properties of germanium (eka-silicon).State Modern Periodic Law.
The properties of elements are a periodic function of their atomic numbers.Trends in Atomic Size:
- Decreases across a period due to increasing nuclear charge.
- Increases down a group due to added shells.
Why do noble gases have zero valency?
Noble gases have a stable electronic configuration with a complete outer shell (octet).
Most Important MCQs Science Class 10 For the 2025 Board Examination
MCQs on Chapter 5: Periodic Classification of Elements
Who proposed the Modern Periodic Table?
A. Dmitri Mendeleev
B. John Newlands
C. Henry Moseley
D. Antoine Lavoisier
Answer: CIn the Modern Periodic Table, elements are arranged in order of:
A. Increasing atomic mass
B. Increasing atomic number
C. Decreasing atomic number
D. Increasing valency
Answer: BWhich of the following is a halogen?
A. Sodium
B. Bromine
C. Magnesium
D. Argon
Answer: BAtomic size decreases across a period because:
A. Number of shells increases
B. Nuclear charge increases
C. Valence electrons increase
D. Atomic mass increases
Answer: BThe element in Group 2, Period 3 of the Modern Periodic Table is:
A. Magnesium
B. Calcium
C. Sodium
D. Potassium
Answer: AWhich element has the highest electronegativity in the periodic table?
A. Fluorine
B. Oxygen
C. Nitrogen
D. Chlorine
Answer: AAn element with atomic number 15 belongs to which group in the Modern Periodic Table?
A. Group 13
B. Group 14
C. Group 15
D. Group 16
Answer: CWhich property increases down a group in the Modern Periodic Table?
A. Ionization energy
B. Electronegativity
C. Metallic character
D. Non-metallic character
Answer: C