Question

Why is centripetal force acts on electron why not centrifugal force?

Answer 1

Let us first clear up the matter of centripetal vs. centrifugal force. The presence of the centrifugal force depends on which frame of reference we are using. When viewed from an inertial reference frame (i.e. that of the nucleus), a body in circular motion only requires a centripetal force (i.e. a force directed towards the centre of the circle). However, to apply the inertial laws of motion from the electron's point of view (i.e. a non-inertial reference frame) we must include an 'imaginary' pseudo-force, which is the centrifugal force. If you have a look through this forum, you'll find plenty of threads discussing the differences between the centripetal and centrifugal forces. You can also take a look at the related articles in the PF library. With respect to the equilibrium comment, I agree with you, the centripetal force is not a component but rather a requirement for circular motion. However, I think perhaps that you are misreading what the author means by equilibrium condition and I certainly don't think that he/she would have [intentionally] presented the centripetal force as a component. Do you agree that for an object of mass m m, moving at velocity v v in a circle of radius r r the net force F net Fnet must obey the following equality? F net = m v 2 r Fnet=mv2r Assuming that you agree, then this is indeed an equilibrium condition. If the net force was greater or less than this then a orbit would be unstable. If you consider the above a valid equilibrium condition then it logically follows that one could also consider the following an equilibrium condition: F net − m v 2 r = 0 Fnet−mv2r=0 I hope this helps. 

Reference https://www.physicsforums.com/threads/centripetal-force-for-an-electron.242836/

Answer 2

Answer:

The centripetal force is just the electrostatic binding potential of the nucleus. It's a centripetal force under the approximation that the nucleus is fixed at the centre of the atom. The centrifugal force is no a true force. It is the consequence of the inertia of some particle undergoing centripetal acceleration.