# Do really the electrons could only orbit in specific orbits with a fixed radius?

According to Bohr's model of atom

The electrons could only orbit the nucleus in specific orbits or shells with a fixed radius. Only shells with a radius given by the equation below would be allowed, and the electron could not exist in between these shells.
r(n)=n​2 ​​ ⋅r(1)

But when I learnt about different orbitals inside the atom in my textbook, it was said that you cannot precisely tell the location of an electron, as you know the velocity, according to Heisenberg's uncertainty principle. Besides in a video of khanacademy.org Sal said that orbitals means that if we took a number of snapshots of atoms, we would see that the electrons are denser in those orbitals but that does not necessarily mean that we wouldn't find it outside of the orbitals. The probability of finding electrons is higher in the orbitals but not 100%. But Bohr said electrons are quantized. It must be in a fixed orbital with a fixed radius. Isn't that contradictory? Which one is true? Or what is wrong in my understanding?

• Forget about Bohr's model. It is but of historical importance, much like phlogiston theory. Commented Dec 11, 2015 at 10:00
• chemistry.stackexchange.com/questions/32860/… Commented Dec 11, 2015 at 10:02
• "According to Bohr's model of atom" -- If the model was accurate, it wouldn't have been replaced, no? Commented Dec 11, 2015 at 10:49

Bohr said electrons are quantized. It must be in a fixed Orbital with a fixed radius. Isn't that contradictory?

"Quantized" means that a continuous range of a variable, such as energy, is not allowed. Only discrete values of the variable are allowed.

In Bohr's model, the radii and energies were quantized.

Which one is true?

It is not true that electrons orbit in fixed circular orbits. Subsequent to the Bohr theory, there was Sommerfeld theory, which involved elliptical orbits and was a relativistic theory that correctly predicted the fine structure of the hydrogen atom (which Bohr's theory did not). Then there was Schrodinger's theory, which did away with the fixed orbits, but was non-relativistic and gave the same energy levels as Bohr's theory. This was followed by Dirac's theory which was a relativistic theory and gave the same energy levels as Sommerfeld's theory. However, the hyperfine structure of the hydrogen atom, such as the Lamb shift, was still not explained, until quantum electrodynamics was developed. Further developments included the recognition that the proton is not a point particle, but is composite. So there has been no finding the truth, just more accurate, but more complex, approximations of the truth.

Sal said that orbitals means that if we took a number of snapshots of atoms, we would see that the electrons are denser in those orbitals but that does not necessarily mean that we wouldn't find it outside of the orbitals. The probability of finding electrons is higher in the orbitals but not 100%

Orbitals have an infinite spatial extent. There are nodes where the wavefunction is zero for the Schrodinger equation solutions of the hydrogen atom, but nodes are specific planes, conical surfaces or spherical surfaces, not 3-dimensional regions. People depict the orbitals as having finite volumes, but these depictions are the high probability regions not the entire orbital. So if Sal said that, he should have said that the electrons can be outside of the high-probability regions of orbitals that people draw, rather than saying outside the orbitals.

I believe Schrodinger's theory is definitely a lot more realistic than Bohr's model. Bohr was not wrong about electrons being quantized. It is definitely true that electrons can only be in one orbital at a time. However, where Bohr was wrong, was to assume that electrons orbit around the nucleus in a circular motion. If this was true, then according to the laws of classical physics, the electrons would continuously lose energy and spiral into the nucleus. Obviously, this does not occur, so we can assume that electrons do not orbit the nucleus. Rather, they exist in these orbitals. Orbitals are more like an electron cloud that surrounds the nucleus. Therefore, it isn't contradictory, it's just that Bohr had some flaws in his model that were later 'fixed' so to speak, in Schrodinger's model. This is not to say though, that Schrodinger's model was perfect. As above comments have stated, there are theories that were developed after Schrodinger's that were definitely even more clear and advanced.

I hope this helped!