A quote first :
A scientist is an atoms way of understanding other atoms !! 🙂
Have you ever wondered what holds the nucleus together ? The nucleus of an atom contains +ve cherged protons and neutral neutrons . Why dont the +ve charges just repel each other and break the nucleus ?
To understand this we will first have to understand something called :
Exchange Force . Lets imagine 2 particles of one kind P1 and P2 and a different kind of particle D . Now D can be close to P1 or D can be close to P2 . ie either bound to P1 or P2 . See diagram
State 1 :
P1 D P2
State 2 :
P1 P2 D
Now the position of D is uncertain ! if P1 and P2 are close then the particle D can flip flop between P1 and P2 ie sometimes be closer to
P1 and sometimes be close to P2 . This is a nice thing for D . This gives D more freedom . According to Pauli’s exclusion principle the system has less energy .
If P1 and P2 are very far away then D has to remain attached to either P1 pr P2 and going to the other particle is hard ( it is too far away !) D does not like this . This state is a high energy state .
So Physics prefers P1 and P2 to bew close to help D get more freedom .
So P1 and P2 attract each other . They attract each other by the
exchange of the particle D .
Similarly the Neutron and the proton attract each other by the exchange
of a particle called meson . The proton gives up a meson and becomes a
neutron . The meson is taken by the nearby neutron which becomes a
proton . So the proton and neutron try to come close to exchange more
This attraction is very strong . In fact it is the strongest
force known in nature !! It is 10 raised to the power 41 times stronger
than gravity !!!!!!! It is called the strong nuclear force .
Does this also answer the question why nuclei have almost equal numbers
of protons and neutrons !!!???
But the problem is that is a very short distance foorce . It operates over
very short distances . If the proton and the neutron are very very
close then this force is important .
This is why heavier nuclei like uranium are so unstable . The reason is
that the nucleus is so large that the repulsion between the far off
protons beats the nucleur attraction between the far off proton – neutron
pair . So all large nuclei are unstable . Infact there cannot be a nucleus
with a Atomic number of 120 !!!!