Periodic Classification of Elements Class 10 Notes: Chemistry becomes much easier when we understand how elements are arranged and related to each other. Periodic Classification of Elements is one of the most important chapters in Class 10 Science. It helps students understand patterns in properties like atomic size, valency, metallic and non-metallic character. This chapter is very important for CBSE board exams and competitive exams.
अगर आप आवर्त सारणी को आसान तरीके से समझना चाहते हैं, तो यह पोस्ट आपके लिए बहुत उपयोगी है। यहाँ आपको सरल भाषा में नोट्स, महत्वपूर्ण ट्रेंड्स, MCQs, Assertion-Reason और Case Study Questions मिलेंगे, जो आपकी तैयारी को मजबूत बनाएंगे। For MCQs, Visit Learneasily8.
Need for Classification (वर्गीकरण की आवश्यकता)
- More than 100 elements exist
- Difficult to study individually
- Helps in grouping similar elements
- Makes learning simple and systematic
👉 इसलिए वैज्ञानिकों ने तत्वों को व्यवस्थित करने के लिए आवर्त सारणी बनाई।
Early Classification of Elements (प्रारंभिक वर्गीकरण)
Dobereiner’s Triads (डोबेरेनर के त्रिक)
- Group of 3 elements
- Middle element mass = average of other two
Example: Li, Na, K
Newlands’ Law of Octaves (न्यूलैंड का अष्टक नियम)
- Every 8th element has similar properties
- Based on musical notes
👉 Limitation:
- Worked only up to Calcium
- Failed for heavier elements
Mendeleev’s Periodic Table (मेंडलीफ की आवर्त सारणी)
Mendeleev’s Periodic Law
Properties of elements are periodic functions of their atomic masses.
Achievements
✔ Left gaps for new elements
✔ Predicted properties (Gallium)
✔ Corrected atomic masses
Limitations
- Position of hydrogen unclear
- Isotopes not explained
- Arrangement issues based on mass
Modern Periodic Table (आधुनिक आवर्त सारणी)
Modern Periodic Law
Properties of elements are periodic functions of their atomic numbers.
Structure of Periodic Table
| Feature | Description |
|---|---|
| Periods | 7 (horizontal rows) |
| Groups | 18 (vertical columns) |
Important Terms
Period (आवर्त)
- Horizontal rows
- Same number of shells
Group (समूह)
- Vertical columns
- Same valence electrons
READ ALSO: Carbon and Its Compounds – Complete Notes (Class 10)
Periodic Trends (आवर्त प्रवृत्तियाँ)
1. Atomic Size (परमाणु आकार)
- Across period → decreases
- Down group → increases
👉 Reason: Nuclear charge increases across period
2. Metallic Character (धात्विक गुण)
- Decreases across period
- Increases down group
👉 Metals lose electrons easily
3. Non-Metallic Character (अधात्विक गुण)
- Increases across period
- Decreases down group
👉 Non-metals gain electrons
4. Valency (संयोजकता)
- Across period: increases then decreases
- Down group: remains same
Position of Hydrogen (हाइड्रोजन की स्थिति)
- Similar to Group 1 (alkali metals)
- Similar to Group 17 (halogens)
👉 Therefore, hydrogen has a unique position
Important MCQs (Most Expected)
- Modern periodic table is based on:
(a) Mass (b) Atomic number (c) Density (d) Volume
Answer: (b) - Atomic size across period:
(a) Increase (b) Decrease (c) Same (d) Random
Answer: (b) - Metallic character across period:
(a) Increase (b) Decrease (c) Same (d) None
Answer: (b) - Number of groups:
(a) 7 (b) 8 (c) 18 (d) 16
Answer: (c) - Valency in group remains:
(a) Same (b) Increase (c) Decrease (d) Zero
Answer: (a)
Assertion–Reason Questions
Direction:
For each question, choose the correct option:
(A) Both Assertion and Reason are true, and Reason is correct explanation
(B) Both are true, but Reason is not correct explanation
(C) Assertion is true, Reason is false
(D) Assertion is false, Reason is true
Q1. Assertion: Elements in the same group have similar chemical properties.
Reason: They have the same number of valence electrons.
Answer: (A)
Q2. Assertion: Atomic size decreases across a period.
Reason: Nuclear charge increases across the period.
Answer: (A)
Q3. Assertion: Metallic character increases down a group.
Reason: Atomic size decreases down the group.
Answer: (C)
Q4. Assertion: Non-metallic character increases across a period.
Reason: Tendency to gain electrons increases.
Answer: (A)
Q5. Assertion: Valency remains the same down a group.
Reason: Number of shells increases down the group.
Answer: (B)
Q6. Assertion: Mendeleev arranged elements according to atomic number.
Reason: Atomic number determines properties of elements.
Answer: (D)
Q7. Assertion: Isotopes cannot be placed in Mendeleev’s table properly.
Reason: Isotopes have same atomic mass.
Answer: (C)
Q8. Assertion: Hydrogen shows properties of both alkali metals and halogens.
Reason: Hydrogen has one electron in its outermost shell.
Answer: (A)
Q9. Assertion: Atomic radius increases down the group.
Reason: Number of electron shells increases.
Answer: (A)
Q10. Assertion: Elements in the same period have the same number of valence electrons.
Reason: Elements in same period have same number of shells.
Answer: (D)
Q11. Assertion: Chlorine is more non-metallic than sodium.
Reason: Chlorine has higher electronegativity than sodium.
Answer: (A)
Q12. Assertion: In modern periodic table, elements are arranged in increasing atomic number.
Reason: Atomic number is equal to number of protons.
Answer: (B)
Q13. Assertion: Noble gases are placed in group 18.
Reason: They have completely filled outer shells.
Answer: (A)
Q14. Assertion: Size of atoms decreases from left to right in a period.
Reason: Electrons are added to the same shell.
Answer: (A)
Q15. Assertion: Metals form positive ions.
Reason: Metals lose electrons easily.
Answer: (A)
Q16. Assertion: Non-metals form negative ions.
Reason: Non-metals gain electrons.
Answer: (A)
Q17. Assertion: Reactivity of metals increases down the group.
Reason: Ionization energy decreases down the group.
Answer: (A)
Q18. Assertion: Reactivity of non-metals decreases down the group.
Reason: Tendency to gain electrons decreases.
Answer: (A)
Q19. Assertion: Elements with similar properties are placed in the same period.
Reason: They have same valence electrons.
Answer: (D)
Q20. Assertion: Mendeleev left gaps in his periodic table.
Reason: He predicted undiscovered elements.
Answer: (A)
Q21. Assertion: Fluorine is the most electronegative element.
Reason: It has smallest atomic size in its group.
Answer: (A)
Q22. Assertion: Alkali metals are highly reactive.
Reason: They have one valence electron.
Answer: (A)
Q23. Assertion: Halogens are very reactive non-metals.
Reason: They need one electron to complete octet.
Answer: (A)
Q24. Assertion: Atomic number determines position of element in modern periodic table.
Reason: Atomic number equals number of electrons in neutral atom.
Answer: (A)
Q25. Assertion: Periodic classification helps in predicting properties of elements.
Reason: Properties of elements are periodic functions of atomic number.
Answer: (A)
Case Study Questions
Case Study 1: Modern Periodic Table
Passage (English):
The modern periodic table arranges elements according to their atomic number. Elements in the same group have similar properties due to the same number of valence electrons. As we move across a period, atomic size decreases, while non-metallic character increases.
हिंदी:
आधुनिक आवर्त सारणी में तत्वों को उनके परमाणु क्रमांक के अनुसार व्यवस्थित किया गया है। एक ही समूह के तत्वों के गुण समान होते हैं क्योंकि उनके संयोजक इलेक्ट्रॉन समान होते हैं। आवर्त में जाने पर परमाणु आकार घटता है और अधात्विक गुण बढ़ता है।
Questions:
- What is the basis of modern periodic table?
(a) Atomic mass
(b) Atomic number
(c) Density
(d) Valency
Answer: (b) - Why do elements in same group show similar properties?
(a) Same shells
(b) Same atomic size
(c) Same valence electrons
(d) Same mass
Answer: (c) - Atomic size across a period:
(a) Increases
(b) Decreases
(c) Constant
(d) Irregular
Answer: (b) - Non-metallic character across a period:
(a) Decreases
(b) Increases
(c) Same
(d) Random
Answer: (b) - Number of periods in modern periodic table:
(a) 6
(b) 7
(c) 8
(d) 18
Answer: (b)
Case Study 2: Mendeleev’s Periodic Table
Passage (English):
Mendeleev arranged elements based on atomic mass and left gaps for undiscovered elements. He predicted properties of elements like gallium. However, his table had limitations such as improper position of hydrogen and inability to explain isotopes.
हिंदी:
मेंडलीफ ने तत्वों को परमाणु द्रव्यमान के आधार पर व्यवस्थित किया और नए तत्वों के लिए स्थान खाली छोड़ा। उन्होंने गैलियम जैसे तत्वों के गुणों की भविष्यवाणी की। लेकिन उनकी सारणी में कुछ कमियाँ थीं जैसे हाइड्रोजन की स्थिति और समस्थानिकों का सही स्थान।
Questions:
- Mendeleev arranged elements based on:
(a) Atomic number
(b) Atomic mass
(c) Valency
(d) Density
Answer: (b) - Why did Mendeleev leave gaps?
(a) Lack of space
(b) For decoration
(c) For undiscovered elements
(d) Mistake
Answer: (c) - Which element was predicted by Mendeleev?
(a) Sodium
(b) Gallium
(c) Oxygen
(d) Nitrogen
Answer: (b) - One limitation of Mendeleev’s table:
(a) No groups
(b) No periods
(c) Hydrogen position unclear
(d) No elements
Answer: (c) - Isotopes problem arises because:
(a) Same atomic number
(b) Same atomic mass
(c) Same valency
(d) Same size
Answer: (b)
Case Study 3: Periodic Trends
Passage (English):
Atomic size increases down a group due to addition of shells. Metallic character also increases down the group. However, across a period, atomic size decreases due to increased nuclear charge.
हिंदी:
समूह में नीचे जाने पर इलेक्ट्रॉन परतें बढ़ने के कारण परमाणु आकार बढ़ता है। धात्विक गुण भी बढ़ता है। लेकिन आवर्त में जाने पर नाभिकीय आवेश बढ़ने के कारण परमाणु आकार घटता है।
Questions:
- Atomic size down a group:
(a) Decreases
(b) Increases
(c) Same
(d) Random
Answer: (b) - Reason for increase in atomic size down group:
(a) Less electrons
(b) More shells
(c) Less protons
(d) Less energy
Answer: (b) - Metallic character down group:
(a) Decreases
(b) Increases
(c) Same
(d) None
Answer: (b) - Across a period, nuclear charge:
(a) Decreases
(b) Increases
(c) Constant
(d) Zero
Answer: (b) - Atomic size across period:
(a) Increases
(b) Decreases
(c) Same
(d) Random
Answer: (b)
Case Study 4: Position of Hydrogen
Passage (English):
Hydrogen shows similarities with both alkali metals and halogens. Like alkali metals, it loses one electron, and like halogens, it can gain one electron. Therefore, its position in the periodic table is unique.
हिंदी:
हाइड्रोजन में क्षार धातुओं और हैलोजन दोनों के गुण पाए जाते हैं। यह एक इलेक्ट्रॉन खो सकता है और एक इलेक्ट्रॉन प्राप्त भी कर सकता है। इसलिए इसकी स्थिति विशेष है।
Questions:
- Hydrogen resembles:
(a) Only metals
(b) Only non-metals
(c) Both
(d) None
Answer: (c) - Hydrogen can lose:
(a) 2 electrons
(b) 1 electron
(c) 3 electrons
(d) 0
Answer: (b) - Hydrogen can gain:
(a) 1 electron
(b) 2 electrons
(c) 3 electrons
(d) None
Answer: (a) - Position of hydrogen is:
(a) Fixed
(b) Unique
(c) Same as sodium
(d) Same as chlorine
Answer: (b) - Group similar to hydrogen:
(a) 1 and 17
(b) 2 and 18
(c) 3 and 4
(d) 5 and 6
Answer: (a)
Periodic Classification of Elements Class 10 Notes: Conclusion
Periodic Classification of Elements is one of the most important and scoring chapters in Class 10 Science. It not only helps students understand the structure of elements but also builds a strong foundation for higher studies in chemistry.
👉 अगर आप इस chapter को अच्छे से समझ लेते हैं, तो Chemistry आपके लिए बहुत आसान हो जाएगी।