model of atom

DAY 1
28.4.20
6th period

Good Morning Boys, 
We have discussed some of the basic concepts of structure of atom in the 4 th period. We have revised the main points of Thomson model of atom , now would be discussing Rutherford  model of atom and about electromagnetic radiations.

Note   : Day 3 i.e 30.4.20 short assestment MCQ will be conducted on the topic of concentration of solution.
Learning Objectives:
students will be able to

• Describe Rutherford  model  of atom.
• List the merits and demerits of Rutherford models of atom.
• Define terms used in defining characteristics of wave.

RUTHERFORD SCATTERING EXPERIMENT:  
He took a Gold foil and passed Alpha rays through it. The source of these Alpha rays was radioactive substance.

                 Observations 

a. Most of the α- particles passed through gold foil undeflected

b. A small fraction of α- particles got deflected through small angles & large angles.

c. Very few α- particles suffered large deflection nearly180^{o    i.e}  rebound back.

1. 
   

  

Conclusion drawn:

  a.most of the  space in an atom is empty.
b. There is positively charged mass present in atom occupying very small space
c.  bouncing back of α-particles from metal foil were due to  direct collision with positively charged mass in atom.
He said,
Atom is electrically neutral.
Nucleus is in center containing protons & neutrons 
 Electrons revolve like planets around the nucleus.

Merits :
1. Explained the position of nucleus . 
2. Explained motion of electron around the nucleus in fixed orbits. 
3.Explained  electrostatic forces of attraction between electron and nucleus.

Drawbacks of Rutherford’s model of atom : 

1.   failed to explain the stability of an atom”.

2. failed to explain  electronic distribution of electrons around nucleus.

Electromagnetic radiations:

The radiations which are associated with electrical and magnetic fields are called electromagnetic radiations. 

When an electrically charged particle moves under acceleration, alternating electrical and magnetic fields are produced and transmitted. These fields are transmitted in the form of waves. These waves are called electromagnetic waves or electromagnetic radiations.

Properties of electromagnetic radiations:

a.  Oscillating electric and magnetic field are produced by oscillating charged particles.

 These fields are perpendicular to each other and both are perpendicular to the direction of propagation of the wave.
b.  They do not need a medium to travel. That means they can even travel in vacuum.

Characteristics of electromagnetic radiations:

• Wavelength: It may be defined as the distance between two neighbouring crests or troughs of wave. It is denoted by λ.

• Frequency (ν) (nu): It may be defined as the number of waves which pass through a particular point in one second.
• Velocity (v): It is defined as the distance travelled by a wave in one second. In vacuum all types of electromagnetic radiations travel with the same velocity which is 3 ×10 ⁸m/sec. It is denoted by v.
• Wave number : Wave number is defined as the number of wavelengths per unit length.
  Velocity = frequency × wavelength, i.e, c = νλ 
•  Amplitude (a): It is the height of the crest or depth of the trough of a wave.

Thats all for the day. 

Take Care And Stay safe.

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