Class notes board class 12

12 HACKERS KA JUGAAD

Nuclei
Composition of nucleus
The atom consists of central nucleus containing entire positive
charge and almost entire mass. According to accepted Model the
nucleus is composed of protons and neutrons. The proton was
discovered by Rutherford by bombardment of alpha particles on
nitrogen in accordance with the following equation.
N +he + in
I

#
Symbolically a nuclide is written as XorzX where A is the
mass number of Z is the atomic number




The neutron was discovered by J Chadwick by bombardment of
alpha particles on beryllium in accordance with

Bethe- + on

=

A neutron is neutral particle and its mass number is 1
&
The number of protons in the nucleus is called atomic number.
While the number of nucleons is called the mass number.
&

In general mass number is greater than atomic number except for
hydrogen nucleus, where A equals Z
*
Since neutron is neutral, it is used for artificial disintegration

, size of nucleus


according to
experimental observations the radius of
,
the nucleus of an atom of mass number A is
Ry tile R= Rod's

V
=HR3
=

EN RA")3 =


IRA
I =
= RED
I
= constantt
Atomic Masses




Isotopes ,
Isobars and Isotones
-

The nuclides having the same atomic number, but different
mass number are called isotopes
-

The nuclides having the same mass number, but different
atomic number or called isobars
=
The nuclides, having the same number of neutrons are called iso
tones