Atomic Structure

ATOMIC STRUCTURE

Early atomic theroies

Dalton's theroy

Postulates of his theory:

All matter is composed of very small particles, called atoms
Atoms are indestructible
they cannot be created or destroyed
Atoms of the same element are similar to one another and are equal in weight
Chemical combination results from the union of atoms in simple numerical proportions

2. thompson's model

This model dealt with the constitution of atoms and discovered electrons .

In his experiments, he found that:

a stream of particles could be seen moving from cathode to anode
by adding an electric field he foud that the moving charges were negative
All substances have negatively charged particles

From that, he made the first model of an atom: The plum pudding model

3.rutherfords model

The passage of alpha particles, which are actually positively charged HE2+ through a gold foil gave the following information:

Most of the alpha particles passed undeflected indicating that the structure of an atom is largely empty
A sharply defined pencil of alpha rays, became enlarged after passing through the metal foil. This enlargement was interpreted by Rutherford as resulting from deflections of alpha particles by the electric field inside and around the atoms making up the foil.
There were some particles deflected by a full 180 degrees meaning it was a recoil of alpha particles. It could by only produced by a strong positive charge's presence.

However, this model failed because within the atom, the electrons revolving around the nucleus carry relatively high charges and according to the classical theory of electromagnetic radiation, such rotating electrons should continuously emit energy as radiation because of thier motion.

this would eventually lead to it losing all of its kinetic energy and collapsing into its' nucleus

QUANTUM THEORY

OF MAtter

PLANCK'S QUANTUM THEORY

v=c/

E=hc/

e=nHV where n is integral

V=v/

bohrs QUANTUM THEORY

Postulates of Bohr's theory:

An electron can revolve around the nucleus not in any arbitrary orbit but only in certain definite circular orbits.
When travelling in a stable stationary orbit, an electron emits no electromagnetic radiation
Emission occurs when an electron makes a jump from one stationary orbit to another