NIOS Lesson 2 - ATOMIC STRUCTURE

2.1 DISCOVERY OF FUNDAMENTAL PARTICLES OF ATOM

INTEXT QUESTION 2.1

2.2 ATOMIC NUMBER, MASS NUMBER, ISOTOPES AND ISOBARS

INTEXT QUESTION 2.2

2.3 EARLIER MODELS

2.3.1 Thomson’s Model

2.3.2 Rutherford’s Experiment

INTEXT QUESTION 2.3

2.4 ELECTROMAGNETIC RADIATIONS

2.4.1 Characteristic Parameters of Electromagnetic Radiations

2.4.2 Electromagnetic Spectrum

INTEXT QUESTION 2.4

2.5 LINE SPECTRUM

2.5.1 Line Spectrum of Hydrogen Atom

INTEXT QUESTION 2.5

2.6 BOHR’S MODEL

2.6.1 Explanation of Line Spectrum of Hydrogen Atom

INTEXT QUESTION 2.6

2.7 WAVE – PARTICLE DUALITY

INTEXT QUESTION 2.7

2.8 HEISENBERG’S UNCERTAINTY PRINCIPLE

INTEXT QUESTION 2.8

2.9 WAVE MECHANICAL MODEL OF ATOM

2.9.1 Significance of Quantum Numbers

2.9.2 Shapes of Orbitals

INTEXT QUESTION 2.9

2.10 ELECTRONIC CONFIGURATION OF ELEMENTS

2.10.1 Aufbau (or building up) Principle

2.10.2 Pauli’s Exclusion Principle

2.10.3 Hund’s Rule

a) Orbital notation method

b) Orbital diagram method

INTEXT QUESTION 2.10

2.11 STABILITY OF COMPLETELY FILLED AND HALF-FILLED SUBSHELLS

1. Symmetry of Orbitals

2. Exchange Energy

INTEXT QUESTION 2.11

WHAT YOU HAVE LEARNT

TERMINAL EXERCISE

1. (a) What are the three fundamental particles that constitute an atom?

(b) Compare the charge and mass of an electron and of a proton.

2. What do you think is the most significant contribution of Rutherford to the development of atomic structure?

3. What experimental evidence shows the dual nature of light?

(a) Compute the energy of a FM radio signal transmitted at a frequency of 100 MHz.

(b) What is the energy of a wave of red light with l = 670 nm?

4. In what way was the Bohr’s model better than the Rutherford’s model?

5. What are the drawbacks of Bohr’s Model?

6. What led to the development of Wave Mechanical Model of the atom?

7. What do you understand by an orbital? Draw the shapes of s and p orbitals.

8. Explain the Hund’s rule of maximum multiplicity with the help of an example.

Chemistry has been defined as the study of matter in terms of its structure, composition and the properties. As you are aware, matter is made up of atoms, and therefore an understanding of the structure of atom is very important. 

You have studied in your earlier classes that the earliest concept of atom (smallest indivisible part of matter) was given by ancient Indian and Greek philosophers (600-400 BC). At that time there were no experimental evidence. 

The origin of the concept of atom was based on their thoughts on ‘What would happen if we continuously keep dividing matter’. 

John Dalton revived the concept of atom in the beginning of nineteenth century in terms of his atomic theory which successfully explained the laws of chemical combination. 

Later experiments showed that the atom is not indivisible but has an internal structure.

In this lesson you will learn about the internal structure of an atom which will help you to understand the correlations between its structure and properties. 

You would learn about these in the later lessons.

OBJECTIVES

After reading this lesson you will be able to :

• explain the atomic number, isotopes and isobars;

• recognize the fundamental particles of atom;

• describe Rutherford’s experiment and explain its results;

• define electromagnetic radiation;

• list and define the characteristic parameters of electromagnetic radiation;

• discuss line spectrum of hydrogen;

• explain Bohr’s postulates and discuss his model;

• draw energy level diagram of hydrogen atom showing different series of lines in its spectrum;

• to explain the stability of half filled and completely filled orbitals;

• explain wave particle duality of matter and radiation;

• formulate Heisenberg’s uncertainty principle;

• explain the need for quantum mechanical model;

• draw probability pictures of an electron in an atom;

• list quantum numbers and discuss their significance;

• draw the shapes of s, p and d orbitals;

• recognize nodal plane;

• explain Pauli’s exclusion principle;

• define Aufbau principle;

• explain Hund’s rule of maximum multiplicity; and

• explain the stability of half-filled and fully filled orbital.