Electrons and the old quantum mechanics

 INTRODUCTION

John Dalton(1766-1844),regarded as the atom is a hard, dence and smallest indivisible particle of matter.

Cathode Rays:-

if electric discharge from a high potential source is passed through a discharged tube evacuated to pressure around 0.01mm or less, ray are emitted from the cathode,these are called cathode rays.
These rays travel in a straight lines at the right angle to the cathode surface.

They produce mechanical motion in a small paddle wheel placed in their path indicating that they are material particles.

These particles are deflected from their path by electric and magnetic fields showing that they are electrically charged.

These particles are known as electrons.
Ratio of e/m of electrons determined by J.J.Thomson.

The magnetic field is applied at right angles to the direction the beam.

Magnetic force = Beu

B = strength of magnetic field.
e = charge
u = velocity

electron starts moving in a circular path of radius r.

The centrifugal force mv²/r arising from this circular motion is equal and opposite to the magnetic force i.e.

Beu = mv²/r
e/m = u/rb......................................1.

m = electronic mass

when electric field of strength E is also applied

Beu = Ee
or
u = e/B................................................2.

substituting the value of u in equation 1 from equation 2

e/m = E/rB²

value of e/m = 1.75875*10¹¹c/kg

this value is found by thomson.

Thomson awarded the physics nobel prize in 1906 for his work on conduction of electricity by gases.


Comments

Post a Comment

Popular posts from this blog

ELECTRONEGATIVITY

Image
  The tendency of an atom in a compound to attract shared electrons towards itself is known as electronegativity of an atom. Pauling gave an arbitrary scale to measure the electronegativity of different elements. This scale is based upon the calculation of bond energies, In this scale fluorine has the maximum value of electronegativity, i. e. 4.0. whereas noble gases have the minimum value, i. e. 0.0. On Mulliken scale, the average of ionization potential and electron affinity is known as electronegativity. In general, the smaller atoms as well  as the atoms with nearly filled shells of electrons, attract electrons more than larger atoms and are, therefore, more electronegative. Determination of Electronegativity   Pauling's scale: Pauling's   scale of electronegativity is based upon the calculation of bond energies. He considered the formation of AB covalent molecule as:  1/2A2+1/2B2 → AB   1/2(A-A) +1/2 (B-B) → A-B  According to Pauling, the bond dis...
Read more

THE TYPES OF ELEMENTS

 Using electronic    configuration as the criterion ,we ordinarily recognise four general type of elements ; The inert gas elements  THe representative elements  The transition elements  The inner transition elements. "The classification of these elements into these groups is dependent on the extent to which the s,p,d and f orbitals are filled". (1) Inert Gases (a) s and p _orbital of the most shell of these elements are completely filled. The outermost electronic configuration in ns2np6. (b) HElium is also inert but it's electronic configuration is 1s2. (2) Representative or normal elements:- (a) Outermost shell of these elements is incomplete. The number of electrons is the outermost shell is less than eight. (b) Inner shells are complete. (c) s-  and p-block  elements except inert gases are called normal or representative elements. (3) Transition Elements ; (a) Last two shells of these elements namely outermost and penultimate shells are incomp...
Read more