CHEMISTRY IX structure of atom part 3

 Mass Number & Atomic Number

* Atomic Number = Number of Protons or Number of Electrons

* Mass Number =Number of Protons +Number of Neutrons.

* Number of Neutrons = Mass Number - Atomic Number(A-Z)

ELECTRONIC CONFIGURATION OF AN ATOM

* The arrangement of electrons in the shell around the nucleus is called Electronic configuration of an atom.

Basic Principle of Electrons filling in Shell

* The maximum number of electrons that can be accommodated in each shell is 2n2

(n= shell number).

 Maximum number of electrons that can be accommodated in K, L, M, N shells are 2,8,18,32 

respectively.

*  Electrons are filled in the increasing order of energy.

* The maximum number of electrons that can be accommodated in the outermost shell of an atom is 8.

Activity

ACTIVITY

1.Atomic Number of a Chlorine is 17, Mass Number is 35.Find the number of protons electrons and neutrons in the atomWrite the electronic Configuration of the Atom

Answers

 Proton=17

 Electrons =17

 Neutrons = 35-17=18

 Electronic configuration =2,8,7.

Isotopes

Eg:

Isotopes of Hydrogen

Which is the particle that differs in it's number in these atoms?

            Neutron 

IMPORTANCE OF ISOTOPES

* Deuterium isotopes of hydrogen are used in Atomic Reactors.

* Carbon-14 is used to determine the age of fossils and prehistoric objects.

* Phosphorous-31 is used as tracers for identifying the nutrient exchange in plants.

* Iodine-131& Cobalt-60 are used in the medical field for diagnosis and treatment like Cancer and Tumour.

* Uranium-235 is used as a fuel in Atomic reactor