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Science Class 10 - Periodic Classification-Of-Elements Notes

Comprehensive study notes for Class 10 - Periodic Classification-Of-Elements olympiad preparation

Periodic Classification of Elements

Welcome to the chapter on Periodic Classification of Elements for Class 10. In this chapter, you will learn how elements are arranged in the periodic table, the history behind their classification, and the trends and properties that help us understand the behavior of elements. By the end of this chapter, you will be able to explain the importance of the periodic table and use it to predict the properties of elements.

Introduction

There are more than 100 elements known to us. To study them easily, scientists arranged them in a systematic way called the periodic table. The periodic table helps us understand the similarities and differences among elements.

Early Attempts at Classification

  • Dobereiner’s Triads: Groups of three elements with similar properties. The atomic mass of the middle element was nearly the average of the other two.
  • Newlands’ Law of Octaves: Every eighth element had properties similar to the first, like musical notes.

Mendeleev’s Periodic Table

  • Arranged elements in order of increasing atomic mass.
  • Elements with similar properties were placed in the same column (group).
  • Left gaps for undiscovered elements and predicted their properties.

Modern Periodic Table

  • Arranged by increasing atomic number (number of protons).
  • There are 18 groups (vertical columns) and 7 periods (horizontal rows).
  • Elements in the same group have similar chemical properties.

Trends in the Periodic Table

  • Valency: The combining capacity of an element. It changes in a predictable way across a period or down a group.
  • Atomic Size: Decreases across a period and increases down a group.
  • Metallic and Non-metallic Character: Metallic character decreases across a period and increases down a group. Non-metallic character shows the opposite trend.
  • Electronegativity: Increases across a period and decreases down a group.

Importance of the Periodic Table

  • Helps to predict the properties of elements.
  • Makes it easier to study and compare elements.
  • Shows trends and patterns in properties.

Practice Questions

  1. What is the basis of classification in the modern periodic table?
  2. Name two limitations of Mendeleev’s periodic table.
  3. How does atomic size change across a period?
  4. Why are elements in the same group similar?
  5. What is meant by the term “valency”?

Challenge Yourself

  • Draw a simple modern periodic table and mark the position of metals, non-metals, and noble gases.
  • Predict the properties of an element based on its position in the periodic table.

Did You Know?

  • The periodic table is sometimes called the “chemist’s calendar.”
  • Dmitri Mendeleev left gaps in his table for elements that were not yet discovered!

Glossary

  • Atomic Number: The number of protons in an atom.
  • Group: A vertical column in the periodic table.
  • Period: A horizontal row in the periodic table.
  • Valency: The combining capacity of an element.

Answers to Practice Questions

  1. Increasing atomic number.
  2. Position of isotopes was not clear; no fixed place for hydrogen; some elements did not fit the order of atomic mass.
  3. Atomic size decreases from left to right across a period.
  4. Because they have the same number of valence electrons.
  5. Valency is the combining capacity of an element.

The periodic table is your guide to the world of elements—use it to explore and understand chemistry!

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