Chemistry · Structure Of Atom · NEET
In physics, acceleration means any change in the velocity VECTOR, not just a change in speed. An electron going around the nucleus is always changing its DIRECTION, so its velocity keeps changing. That makes it an accelerating charge, even if its speed stays the same. This is the key idea NEET wants you to know.
Maxwell's laws of electromagnetism say that whenever a charged particle accelerates, it sends out electromagnetic waves (radiation). Sending out these waves costs energy. So the orbiting electron slowly loses its energy as radiation. This rule applies to all charges, so Rutherford's electron cannot escape it.
Calculations using classical physics show the electron would lose energy so fast that it would spiral into the nucleus in about 10^-8 seconds (0.00000001 s). That is almost instant. But real atoms last forever, so the model is clearly wrong. NEET sometimes asks this 10^-8 s value.
As the electron loses energy, its orbit gets smaller and smaller, so it moves in a shrinking spiral toward the nucleus. When it finally hits the nucleus, there is no more empty space and the atom is destroyed. Since matter around us is stable, this predicted collapse shows Rutherford's model failed.
It could not explain the LINE SPECTRUM of atoms. A spiralling electron would give off energy of ALL wavelengths continuously (a continuous spectrum). But hydrogen and other atoms give sharp, separate lines. Rutherford's model had no way to explain these fixed lines. Bohr's model fixed both problems.
Bohr said electrons can only stay in certain fixed orbits (stationary states) where they do NOT radiate energy. Energy is given out only when an electron JUMPS from a higher orbit to a lower one, producing sharp spectral lines. This kept the atom stable and explained the line spectrum.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
First, it could not explain the stability of the atom, because an orbiting electron should radiate energy, spiral inward, and collapse into the nucleus in about 10^-8 s. Second, it could not explain the line spectrum of atoms, since it predicts a continuous spectrum instead of sharp lines.
As the electron spirals inward, its orbit shrinks smoothly, so it would emit radiation of continuously changing wavelength. This gives a continuous band of colours. But real atoms give a line spectrum with only certain fixed wavelengths, which the model cannot explain.
No. Rutherford's alpha-scattering experiment correctly discovered the tiny, dense, positively charged nucleus. That part is still accepted today. Only his idea about electron motion had drawbacks, which Bohr and later quantum mechanics fixed.
Yes, it is called the planetary model because electrons orbit the nucleus like planets orbit the Sun. But planets are neutral, while electrons are charged, so electrons radiate energy and cannot stay in stable orbits the way planets do.
