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### Course: Modern Physics (Essentials) - Class 12th>Unit 3

Lesson 2: What makes neon signs glow in different colors?

Using equation for Bohr model radii to draw shell model for n=1 to 3, and calculating the velocity of a ground state electron.

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Created by Jay.

## Want to join the conversation?

• Is this equation applicable only hydrogen atom?
• According to the equation - rn = n2*r1
the radius when n = 1 =1*r1
the radius when n = 2 =4*r2
the radius when n = 3 =9*r3
So distance between K and L shell = 3r1
Distance between L and M shell is 5r1
However in periodic table we learn that the distance between the shells of an atom keep on decreasing but here they are increasing.
How?
Thanks.
• Again, you can’t apply the Bohr model to other atoms.
• If the electrons have a specific range of distance from the nucleus, then that would mean that an electron could be actually anywhere inside that fixed "donut-shaped" orbit. Wouldn't it be very difficult for scientists to predict the actual position of an electron at a given time ?
• It is.
But the orbits aren't donut shaped.
And the Bohr model is not an accurate model.
• What are principal quantum numbers?
• principal quantum number is one of the four quantum numbers used to describe energy levels in the atom. it can have values n=1,2,3,4... and it determines the size of an orbital.
• FROM where did the Rydberg constant derived?
• Would the radius of the n= ∞ energy level be infinity?
(1 vote)
• If you had to do this with the flow of the cell through the veins between the Right ankle to the left, How would you write that out? Since atom's function don't touch anything?
(1 vote)
• The idea that atoms are mostly empty space or that nothing touches at an atomic level is not really accurate. Saying this you are using the loose idea of what empty space is and what it means to touch something in everyday life and not a technical scientific definition of what empty and touching means.

What is empty space? The concept of something occupying space come from our everyday concept of physical objects occupying a volume of space and that there is something there. When you start to look at things at an atomic and sub-atomic scales this idea starts to break down. Fundamental particles are essentially points with no volume that have associated fields that may or may not interact.

Saying that that matter particles don't ever occupy the same space and interact via fields but this is also true at every day macroscopic scales as well.

From a scientific perspective when you touch the surface of a table the electromagnetic fields and the Pauli exclusion principle come into play. As your finger gets closer to the table there is a slightly attractive force between the outer electrons in the atoms in your finger and the table and the nuclei in these atoms, this is called the van der Waals force. As the atoms in your finger and the table get even closer the Pauli exclusion principle begins to push the electrons in the atoms of your finger and the table apart. It is at the point where the Van der Waals force and the force from the Pauli exclusion principle cancel each other out it when your finger is technically touching the table.

So in the end the idea that matter is just empty space and things don't touch is not an accurate statement. It is using the more flexible common speech definition of touch in a way that it it doesn't apply.
• Is the radius REALLY a vector? I have a hard time visualizing it as such, and wonder if it isn't a scalar instead?
(1 vote)
• I am not sure where in the video they refer to the radius as a vector. If you are assuming that because they put and arrow as the radius that may be the use of an engineering diagram convention of using an arow to show a dimension length.

There are cases where radius is used as a scalar and others where it is used as a vector. It sort of depends on the situation. For example is you are calculating the volume of a sphere r is scalar but when you are calculating the angular momentum of an object in circular motion it is a vector.
• does n represent the periods of the periodic table ? if not what ?