Atomic Structure

UNIT 12

ATOMIC STRUCTURE

Learning Objectives

After the completion of this lesson, students will be able to:

• understand the advantages and limitations of Dalton’s atomic theory.

• distinguish the fundamental particles and their properties

• get an idea about Thomson’s atom model and its limitations

• calculate the valency of different elements.

• write the chemical formula and molecular formula of compounds.

• balance the chemical equations.

• state the laws of chemical combinations.

Introduction

 Every substance in our surrounding is made up of unique elements. There are 118 elements identified worldwide so far. Out of these elements, 92 elements occur in the nature and the remaining elements are synthesised in the laboratories. Copper, Iron, Gold and Silver are some of the elements found in the nature. Elements like Technetium, Promethium, Neptunium and Plutonium are synthesised in the labaratories. Each element is made up of similar, minute particles called atoms. For example, the element gold is made up of gold atoms which determine its characteristics. The word atom is derived from the Greek word atomos. Tomos means smallest divisible particle and atomas means smallest indivisible particle. Ancient Greek philosophers like Democritus, have spoken about atoms. Evenour Tamil poet Avvaiyar has mentioned about atoms in her poem while describing Thirukkural (அணுவைத் துளைத்து ஏழ் கடலைப்புகட்டிக் குறுகத்தரித்த குறள்). But, none of them have scientific base. The first scientific theory about atom wasgiven by John Dalton. Followed by him, J.J.Thomson and Rutherford have given theirtheory about atom. In this lesson, we will studyhow atomic theories evolved at different times.We will also study about valency, molecularformula, rules for naming chemical compounds and balancing chemical equations.