Name:-Ms.SHAIKH YASMIN RASHIDDate:-16 SEPTEMBER 2012Std:-VIIISub:-ScienceCHAPTER:-THE STRUCTURE OF AN ATOMa)theories of an atomb)particles of an atomc)atomic no and atomic mass nod)isotopesReference:- 1)google.Com 2)wikipedia 3)yahoo.Com

STRUCTURE OF AN ATOM

EVERY SUBSTANCE IS MADE UP OF AN ATOM

DALTON’S ATOMIC THEORY(1808)

Atom is a hard and solid ball

LIMITATIONS OF DALTON’S THEORY It does not propose anything about

positive and negative charge

THOMSON’S THEORY

Compared an atom with watermelon

RUTHERFORD’S EXPERIMENT

BOMBARDED THIN LAYER OF GOLD WITH ALPHA PARTICLES

RUTHERFORD’S THEORY Nucleus at the centre has positive

charge Negatively charged electrons revolve

around the nucleus Nucleus is very very small as compared

to atom

STAGES OF DISCOVERY OF THE CONSTITUNT OF AN ATOM

Dalton Thomson Rutherford

FUNDAMENTAL PARTICLES OF AN ELEMENT:-Proton +ve charge 1Neutron no charge 1

Electron -ve charge nil

ATOM IS ELECTRICALLY NEUTRALAs the number of electron=no of proton

No of +ve charge = No of negative charge

ATOMIC NEMBER(Z):NO OF ELECTRON

Atomic no of oxygen=8

ATOMIC NUMBER(Z):-

HYDROGEN-1 HELIUM-2

ATOMIC NUMBER(Z):-

LITHIUM-3 CHLORINE-17

ATOMIC MASS NUMBER(A):-SUM OF PROTON AND NEUTRON

ATOMIC MASS NUMBER(A)

ISOTOPES:-ATOMS HAVING SAME ATOMIC NO BUT DIFFERENT ATOMIC MASS NO

ISOTOPES OF HYDROGEN

ISOTOPES OF CARBON

LEARNING CHECKState the number of protons for atoms

of each of the following:A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons

B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons

C. Barium1) 137 protons 2) 81 protons 3) 56 protons

LEARNING CHECK Naturally occurring carbon consists of

three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C14C

6 6 6

#p _______ _______ _______

#n _______ _______ _______

#e _______ _______ _______