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Periodic Table and Atomic Properties — Syllabus

Telangana Open School (TOSS) · Class 12 · Chemistry

What Periodic Table and Atomic Properties covers in Telangana Open School (TOSS) Class 12 Chemistry: 4 topics, for the 2026-27 session.

43 questions35 flashcards2 formulas & key relations5 concepts

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4 Topics · Telangana Open School (TOSS) Class 12 Chemistry · 2026-27

Topics in Periodic Table and Atomic Properties

1

Historical Development of the Periodic Table

  • J.W. Dobereiner proposed the Law of Triads: the atomic weight of the middle element in a triad is approximately the average of the other two.
  • J.A.R. Newlands introduced the Law of Octaves, stating that every eighth element has similar properties, like musical notes.
  • Mendeleev's Periodic Table arranged elements by increasing atomic weight and left gaps for undiscovered elements, predicting their properties.
2

Modern Periodic Law and Table Structure

  • Modern Periodic Law: Properties of elements are periodic functions of their atomic numbers.
  • The long form of the periodic table has 18 groups and 7 periods.
  • Elements are classified into s-, p-, d-, and f-blocks based on the subshell in which the differentiating electron enters.
3

Electronic Configuration and Periodicity

  • The period number corresponds to the principal quantum number (n) of the valence shell.
  • Number of elements in a period depends on the number of orbitals being filled: 2 in period 1, 8 in periods 2–3, 18 in 4–5, 32 in 6–7.
  • s-Block: ns¹⁻²; p-Block: ns² np¹⁻⁶; d-Block: (n−1)d¹⁻¹⁰ ns⁰⁻²; f-Block: (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns².
4

Periodic Trends in Atomic Properties

  • Atomic size decreases across a period (left to right) due to increasing nuclear charge pulling electrons closer.
  • Atomic size increases down a group due to addition of new electron shells.
  • Cations are smaller than their parent atoms; anions are larger.

Key Concepts

Central concept: Periodic Table and Atomic Properties

Need for ClassificationModern Periodic LawLong Form of Periodic TableElectronic ConfigurationPeriodic Trends in Atomic PropertiesNomenclature of Elements >100Anomalous Properties of Second Period Elements

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Frequently Asked Questions

What are the important topics in Periodic Table and Atomic Properties for Telangana Open School (TOSS) Class 12 Chemistry?
Key topics in Periodic Table and Atomic Properties include Historical Development of the Periodic Table, Modern Periodic Law and Table Structure, Electronic Configuration and Periodicity, Periodic Trends in Atomic Properties. Study these first, then practise questions on each for the Telangana Open School (TOSS) Class 12 board exam.
How should I revise Periodic Table and Atomic Properties for the Telangana Open School (TOSS) Class 12 board exam?
Learn the core ideas first, then work through the 43 practice questions on Periodic Table and Atomic Properties. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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All Telangana Open School (TOSS) Class 12 Chemistry Syllabus

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