Subimal said:
JitenDa
Are you sure? Or you are guessing! Nuclear forces are short-range forces. Moreover, electrons are not nuclear particles. How can they experience nuclear force? Do nuclear particles really exert any nuclear force on the electrons?
It is the nuclear protons with positive charge that exert electrostatic attractive force (relatively longer range force) on negatively charged electrons. And this attractive electrostatic force keeps electrons revolving around the nucleus. Compare this with the attractive gravitational force that keeps the earth revolving around the sun.
Please correct me if I am wrong.
With regards.
------Subimal
My Response:
According to the model proposed by Neils Bohr in 1913, electrons revolve around the nucleus in specific orbits and are prevented from leaving the atom by the centripetal force of attraction between the positively charged nucleus and the negatively charged electrons.
This centripetal force has to be balanced by the centrifugal force of the electron to stay in the particular orbit. Otherwise, electron will collapse into the nucleus due to the attraction. The centrifugal force is given by,
F = mev2/r (1)
Where, m is the rest mass (~10-31 kg) of the electron, v is the velocity of the electron, and r is the radius of the orbit. As you can see, electrons has to move with a certain velocity to stay in a particular orbit, just like planets. If their velocities change, they have to adjust their orbits (r) to counter balance attractive forces, otherwise they will collapse on to the attracting central object. The arrangement of electrons outside the nucleus is governed by the rules of quantum mechanics and Pauli exclusion principle.
In case of a planet, the centripetal force is provided by the gravitational force, and their arrangements in the orbit are not guided by any quantum mechanical principles. The centrifugal force arises from their velocities. Quantum mechanical particles follow the uncertainty principle developed by Heigenberg in 1927. According to this principle, it is impossible to specify precisely and simultaneously the values of both members of particular pairs of physical variables that describe the behavior of an atomic system.
These pairs are,
Dx.D px>= h/2p (2)
Dt.DE >= h/2p
Df.D Jz>= h/2p
For a classical particle, the above uncertainties do not arise. For example, one can measure position and momentum simultaneously at an instant from the knowledge of its position and momentum at a prior instant. This cannot be done in case of quantum particles. They are minute particles; their states change during each observation.
Sometimes electrons are born inside the nucleus, when a neutron decays into a proton, an electron, and a neutrino. The electrons and neutrinos are emitted instantaneously from the nucleus because of their intrinsic speed which requires an orbital radius that is bigger than the nuclear radius (~10-14 m).
The binding energies of the orbital electrons in various shells depend on the magnitude of Coulomb force of attraction between the nucleus and the orbital electrons. Electrons in the inner shells are strongly bound and the ones on the outer shell are loosely bound. Outer shell electrons are called valence electrons, which are responsible for chemical bonding between atoms. The inner shell electrons are responsible for characteristic X-rays.
There are free electrons also, which are not bound to an atomic orbit. For example, we can release electrons from the tungsten filament by heating. Some of those emitted electrons can be used to produce visible light; others can be used to provide radiation beams to treat cancer patients. There is another phenomena, called pair production, in which a photon with energy 1.02 Mev is absorbed by the matter to produce an electron (e-) and a positron (e+), and these two particles can be annihilated to produce two photons with energies 0.51 MeV. This phenomena tells us that electron and photon are interchangeable and exhibit similar characteristics.
That's all folks for today.
Regards,
Jiten Roy
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