Introduction
The Periodic Table is one of the most important concepts in Chemistry because it organizes all known elements according to their atomic numbers and recurring chemical properties. In Class 9 Chemistry Chapter 3, students learn about the development of the periodic table, the contributions of Dmitri Mendeleev and Henry Moseley, modern periodic law, groups and periods, and the classification of elements into different blocks. The chapter also explains important periodic trends such as atomic size, ionization energy, electronegativity, and the properties of different element groups.
Understanding the periodic table helps students predict the physical and chemical properties of elements without memorizing each one individually. These concepts form the foundation for many later Chemistry chapters and are frequently tested in school examinations and board exams.
On this page, you will find carefully selected Class 9 Chemistry Chapter 3 MCQs with answers and explanations, along with learning outcomes, quick revision notes, important definitions, important concepts, exam tips, and common mistakes to help you prepare effectively for your examinations.
Learning Outcomes
After studying this chapter, students will be able to:
- Explain the modern periodic law.
- Describe the contributions of Mendeleev and Moseley.
- Differentiate between groups and periods.
- Explain periodic trends in atomic properties.
- Identify different blocks of the periodic table.
- Recognize the characteristics of important element groups.
- Prepare confidently for Class 9 Chemistry examinations.
Quick Notes – Chapter Summary
- The modern periodic table arranges elements according to increasing atomic number.
- Dmitri Mendeleev proposed the first widely accepted periodic table based on atomic masses.
- Henry Moseley improved the periodic table by arranging elements according to atomic number.
- Vertical columns are called groups, while horizontal rows are called periods.
- Elements in the same group have similar chemical properties because they possess the same number of valence electrons.
- Atomic radius generally decreases across a period and increases down a group.
- Ionization energy generally increases across a period and decreases down a group.
- Electronegativity generally increases across a period and decreases down a group.
- Group 1 contains alkali metals, Group 17 contains halogens, and Group 18 contains noble gases.
- Transition elements are located in the d-block of the periodic table.
- The periodic table helps predict the physical and chemical properties of elements.
Important Definitions
Periodic Law: The physical and chemical properties of elements are periodic functions of their atomic numbers.
Group: A vertical column in the periodic table containing elements with similar chemical properties.
Period: A horizontal row in the periodic table.
Atomic Number: The number of protons present in the nucleus of an atom.
Atomic Radius: The distance from the nucleus to the outermost electron shell.
Ionization Energy: The energy required to remove the outermost electron from an atom.
Electronegativity: The ability of an atom to attract shared electrons in a chemical bond.
Periodicity: The regular repetition of the physical and chemical properties of elements.
Important Concepts
Characteristics of alkali metals, halogens, and noble gases.
Development of the periodic table.
Modern periodic law.
Groups and periods.
Periodic trends.
Atomic radius.
Ionization energy.
Electronegativity.
Classification of elements into s, p, d, and f blocks.
Class 9 Chemistry Chapter 3 – Periodic Table and Periodicity MCQs
1. Who is credited with formulating the Periodic Law?
- A. John Dalton
- B. Henry Moseley
- C. Dmitri Mendeleev ✅
- D. Antoine Lavoisier
Explanation: Mendeleev arranged elements in increasing atomic mass and observed repeating properties, leading to the Periodic Law.
2. What property did Moseley use to arrange the elements in the modern periodic table?
- A. Atomic mass
- B. Atomic number ✅
- C. Valency
- D. Electron affinity
Explanation: Moseley rearranged elements according to increasing atomic number, which resolved anomalies in Mendeleev’s table.
3. Elements in the same group have:
- A. Same atomic masses
- B. Same number of valence electrons ✅
- C. Same atomic radii
- D. Same densities
Explanation: The same number of valence electrons results in similar chemical properties for elements in the same group.
4. Which period contains only two elements?
- A. 1st period ✅
- B. 2nd period
- C. 3rd period
- D. 4th period
Explanation: The first period has only hydrogen and helium.
5. What happens to atomic size across a period from left to right?
- A. Increases
- B. Decreases ✅
- C. Remains constant
- D. Doubles
Explanation: Increasing nuclear charge pulls electrons closer, reducing atomic size across a period.
6. Which group contains noble gases?
- A. Group 1
- B. Group 2
- C. Group 18 ✅
- D. Group 17
Explanation: Group 18 elements are noble gases with full outer shells, making them chemically inert.
7. Which property increases down a group?
- A. Ionization energy
- B. Atomic radius ✅
- C. Electronegativity
- D. Electron affinity
Explanation: Adding electron shells increases the distance between nucleus and outer electrons, increasing atomic radius.
8. Which element is a halogen?
- A. Oxygen
- B. Chlorine ✅
- C. Neon
- D. Sodium
Explanation: Halogens belong to Group 17 and are highly reactive nonmetals.
9. The horizontal rows in the periodic table are called:
- A. Groups
- B. Periods ✅
- C. Series
- D. Blocks
Explanation: Periods are horizontal rows, each corresponding to the filling of a principal electron shell.
10. Which block contains transition elements?
- A. s-block
- B. p-block
- C. d-block ✅
- D. f-block
Explanation: Transition elements are found in the d-block of the periodic table.
11. What is the periodicity of properties?
- A. Properties change randomly
- B. Properties remain constant
- C. Repetition of properties at regular intervals ✅
- D. Change of state of matter
Explanation: Periodicity is the repeating pattern of chemical and physical properties as elements are arranged by atomic number.
12. Which group of the periodic table contains the alkali metals?
- A. Group 1 ✅
- B. Group 2
- C. Group 17
- D. Group 18
Explanation: Alkali metals are placed in Group 1 and have one electron in their outermost shell, making them highly reactive.
15. Which type of elements are good conductors of heat and electricity?
- A. Metals ✅
- B. Non-metals
- C. Noble gases
- D. Halogens
Explanation: Metals are generally good conductors of heat and electricity because they contain free-moving electrons.
14. Which block of the periodic table contains elements with valence electrons in the p-subshell?
- A. s-block
- B. p-block ✅
- C. d-block
- D. f-block
Explanation: The p-block contains elements whose outermost electrons occupy the p-subshell.
15. Why are noble gases generally chemically inert?
- A. They have low atomic masses.
- B. They have completely filled outermost electron shells. ✅
- C. They easily lose electrons.
- D. They readily react with metals.
Explanation: Noble gases have complete valence shells, making them very stable and chemically unreactive.
16. Which group of elements is known as the alkaline earth metals?
- A. Group 1
- B. Group 2 ✅
- C. Group 16
- D. Group 17
Explanation: Group 2 elements are called alkaline earth metals and have two valence electrons.
17. Which property generally increases across a period from left to right?
- A. Atomic radius
- B. Metallic character
- C. Electronegativity ✅
- D. Number of electron shells
Explanation: Electronegativity generally increases across a period because atoms attract shared electrons more strongly.
18. Which statement about elements in the same period is correct?
- A. They have the same number of valence electrons.
- B. They have the same number of electron shells. ✅
- C. They have identical chemical properties.
- D. They belong to the same block.
Explanation: Elements in the same period have the same number of occupied electron shells, while the number of valence electrons increases from left to right.
19. Which of the following is an alkali metal?
- A. Calcium
- B. Sodium ✅
- C. Magnesium
- D. Aluminium
Explanation: Sodium belongs to Group 1 of the periodic table and is classified as an alkali metal.
20. Metalloids have properties that are:
- A. Similar only to metals
- B. Similar only to non-metals
- C. Intermediate between metals and non-metals ✅
- D. Similar only to noble gases
Explanation: Metalloids show properties of both metals and non-metals and are often used in semiconductor devices.
Exam Tips
– Learn the differences between groups and periods.
– Memorize the important periodic trends.
– Understand why elements in the same group have similar properties.
– Identify the positions of alkali metals, halogens, and noble gases in the periodic table.
– Practice MCQs regularly to improve conceptual understanding.
Common Mistakes
❌ Confusing groups with periods.
❌ Mixing up atomic number and atomic mass.
❌ Forgetting the direction of periodic trends.
❌ Assuming all elements in a period have similar properties.
❌ Confusing halogens with noble gases.
Conclusion
The periodic table provides a systematic way to classify elements and predict their physical and chemical properties. By understanding periodic law, groups, periods, and periodic trends, students can build a strong foundation for future Chemistry topics. Regular revision of the important definitions and concepts, along with consistent practice of these MCQs, will improve conceptual understanding and help achieve better results in school and board examinations.