Model Of Am Atom

Govt.Sen.Sec.School Dalla Ropar       

Project Report on Atomic Structure Prepared by:Class 9th Students Sarabjit Kaur Amandeep Singh Yadwinder Singh Parveen Kaur

Bibliography:  

Microsoft Encarta Internet CBSE Textbooks

Introduction 

An atom is the ultimate indivisible particle of matter that can exit independently. This concept was given by Dalton in the nineteenth century .At that times scientist were questioning whether atoms are really indivisible .It was shown by various experiments discussed below that atom is further made up of three fundamentals particles called Electrons, Protons and Neutrons

Cathode Rays Discovery of Electrons:

Sir J.J Thomson performed a number of experiments on the conductance of electricity through glasses taken in a discharge tube. At very low pressure ,the discharge tube appears completely dark. However the glass walls of the discharge tube at the end of opposite to the cathode start glowing due to the bombardment of the walls of the glass tube by invisible rays which are given out by cathode. These rays are deflected from their path by electric and magnetic fields towards positive field .This proves that particles of the rays possesses

Anode Rays Discovery of Proton 

Elections are negatively charged particles but an atom is electrically neutral .Therefore atom must contain something which is positvely charged to nerrtralise the negative charge of electrons.E. woldstein discovered another type of rays by employing a perforated metal cathode in the discharge tube.positive particles which neither collide with electrons or cathode rays nor strike the surface of cathode but pass through the back of cathode.by deflection of anode rays towards negative plate in electric field it was proved that these rays consist of +vely charged particlas called protons.

Discovery of neutrons :

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For all atoms except hydrogen mass of an atom is more than number of protons. To account for this extra mass Rutherford predicted the existence of some neutral of some neutral particles in the nucleus of an atom having a mass equal to that of proton but carrying no charge .For a long time however the existence of this neutral particle could not be proved .In 1932 Chadwick discovered a new fundamental particle which was having the same mass as that of proton but carrying no charge .He bombarded a thin beryllium foil with high speed alpha particles and get uncharged particles. 9 4 12 + + n10 4Bc 2He -> 6C

Beryllium Neutron

x-particle

Carbon

Model of am Atom In order to investigate the arrangement of the electrons and protons and neutrons in an atom various model of an atom was proposed but Bohr’s model was most accepted one. The important postulates of Bohar’s model are:1. Atom consist of positively charged nucleus contains protons and neutrons present at the Centre occupying a very small space. 2. Electrons revolve in certain definite orbits around the nucleus. 3. As long as electron revolves in a particular orbit it neither emits nor absorb energy. The electrons in an atom can have certain definite values of energy which are characteristic of that atom. 4. Energy is emitted or absorbed by an atom only when an electron moves From one energy level to the other. Since the various energy levels have Certain definite values of energy the refers energy is always emitted or absorbed in definite quantities called quanta.

However later on,on the basis of De brogue's concept of dual nature of matter and Hues berg’s uncertainty Principle concept of fined circular orbits was replaced by concept of three divisional space around nucleus where probability of finding an electron is maximum (orbital)