10th class physics properties of atom,atomic number,nucleon number,neutr...

Greek Philosopher Democritus in 585
BC

postulated that matter is built from small particles called atoms. The atom
means indivisible in Greek language

Atomic
number:

The atomic number Z
is
equal to the number of protons in the nucleus.

Neutron
number:

The neutron number N is equal to the number of neutrons in the
nucleus.

Atomic
mass number or Nucleon number:

The atomic mass number or nucleon number A is equal to the number of nucleons
(protons + neutrons) in the nucleus i.e., A= Z+N.

The
mass of neutron is nearly equal to that of proton. But proton is about 1836
times heavier than an electron. So the mass of an atom is nearly equal to the
sum of masses of protons and neutrons

Isotopes are atoms of an element which
have same number of protons but different number of neutrons in their nuclie.

        protium                deuterium                tritium

Three isotopes of Hydrogen Protium  ((_1^1)H ) 
contains one proton in the nucleus and one electron that revolves round
the nucleus.

Deuterium ((_1^2)H ) contains one proton, one neutron and
one electron.

Tritium ((_1^3)H ) contains one proton, two neutrons and
one electron.