Problem Solving Strategies

5:25 AM

how can we draw the structure of light. Like there are photons inside of it for example. On a pen and paper , how can we draw it.
How should the labelling

Look like

John Rennie

@Sarabsrimt Light is much more complicated than you think.

To properly describe light you need quantum field theory, which is very, very hard!

Sarabsri mt

5:46 AM

Ohh k @JohnRennie

chemistry.stackexchange.com/questions/147205/…

@JohnRennie Sir , this Q

John Rennie

I think what is confusing you is that in metals the electrons are not in orbitals like they are in hydrogen atoms.

Sarabsri mt

Really

Why different

Orbital is electron right. That’s what is in my book

John Rennie

In metals the electrons are in states called energy bands that spread out over the whole metal. The electrons in these bands are not attached to any particular atom but instead are free to move over the whole piece of metal. That's why metals conduct electricity.

Sarabsri mt

Ohk.

Sir , about orbital

John Rennie

In a single atom, like a hydrogen atom, we get well defined states 1s, 2s, 2p, etc and the electrons go into on of these states.

These states are what we call the orbitals.

But in solids where we have lots of atoms close together the states from all the atoms combine to create energy bands that spread out through the solid.

Sarabsri mt

5:52 AM

So ,

metals don’t have orbitals

John Rennie

In the photoelectric effect the electron is coming from the highest energy band, which is called the conduction band.

Sarabsri mt

but liq and gases have

@JohnRennie k

John Rennie

Gases don't have bands because it gases the atoms are generally far apart from each other. Metals have bands because the atoms are close together.

Liquids are kind of in between.

Sarabsri mt

Ohk.

Really nice sir

Just want to confirm certain things now

John Rennie

OK ... ?

Sarabsri mt

5:55 AM

In gases

So , does the photo electric effect happen there

John Rennie

No.

Sarabsri mt

Ohk.

And metals don’t have orbits

like gases and liq (kind of )

John Rennie

Yes

Sarabsri mt

Only metals follow rule of orbitals

John Rennie

Gases you mean?

Gases have orbitals, metals have bands.

Sarabsri mt

5:57 AM

gases and liq follow rule of orbits

Oh yes

@JohnRennie yes

sorry my mistake

@JohnRennie This was very well explained sir. I understood it quite well

@JohnRennie This one I have confusions

John Rennie

OK ... ?

Sarabsri mt

Is there a difference between light ray and photons and EM radiation

Like Light ray and photons are a part of EM radiation right

John Rennie

Again this is surprisingly complicated.

Sarabsri mt

So , what should be the difference in light ray and photons . Both must be having energy

@JohnRennie ohk

John Rennie

It is tempting to think of a photon as a little ball of energy, so a light beam would be a collection of these little balls of energy. But that isn't how it works at all.

Sarabsri mt

6:00 AM

Ohk sir

@JohnRennie Is it ok for a beginner to assume it or some other way he/she can .

John Rennie

@Sarabsrimt a light beam is really a wave. There are no particles in it at all.

But when the light beam exchanges energy with anything else, the energy is exchanged as photons.

Sarabsri mt

Ohk.

Sir , one more thing.

In your link

you have also explained about discrete and continuous spectrum

John Rennie

Yes?

Sarabsri mt

I didn’t understand that. How it happens and why

John Rennie

@Sarabsrimt which link?

Sarabsri mt

6:04 AM

@JohnRennie This one sir

John Rennie

OK.

Sarabsri mt

John Rennie

In an atom the electrons occupy one of the states 1s, 2s, 2p, etc and all of these states have a well defined energy.

Sarabsri mt

Yes sir

John Rennie

The only way an electron can change state is to jump between two states, and the energy needed for that jump is equal to the difference in the energies of the two states.

Sarabsri mt

6:06 AM

Yes

John Rennie

So when you shine light on the atom it can only be absorbed in the photon energy, E = hf, exactly matches the spacing between two states.

This is what I mean by a discrete spectrum. Light isn't absorbed at all frequencies. It is only absorbed at a few frequencies where the light energy matches the spacing between two states.

Sarabsri mt

Ohk

So , an electron in ground state

when goes to excited state

has discrete spectrum

John Rennie

Yes

Have you learned about the hydrogen atom?

Sarabsri mt

I am learning about Niels Bohr model for H atom

Thats it.

John Rennie

You need to bear in mind that the Bohr model is wrong. It was an early attempt to describe atoms, but atoms don't actually work like that.

I think the JEE does include the Bohr model, so you need to know it, but it doesn't describe the way atoms actually work.

Sarabsri mt

6:14 AM

@JohnRennie Umm. So , atoms do have orbits right. I think what is wrong is that electron does not revolve around the orbit

because then , energy is being released every second

@JohnRennie ohk

John Rennie

Elementary particles are not like little balls. They are more like fuzzy clouds i.e. they are spread out in a cloud not located at a point.

Sarabsri mt

Oh yes.

Sir ,

John Rennie

The electron in a hydrogen atom is like a cloud centred on the nucleus.

Sarabsri mt

John Rennie

The difference between the 1s, 2s, etc is that the cloud has a different shape.

Sarabsri mt

6:15 AM

@JohnRennie yes sir. Right

@JohnRennie Yes sir.

@JohnRennie I did see that too

John Rennie

But you don't need to know this stuff for the JEE.

Sarabsri mt

@JohnRennie ohk . I’m more like I spend enough time for jee and also extra

Sir , in these images

the formula that we have

John Rennie

It's interesting to talk about this extra stuff, and it's a good way to make the JEE studies less boring, but you need to be a little careful not to get distracted :-)

Sarabsri mt

@JohnRennie Right sir. With extra stuff , I never get distracted . Not even from inorganic.

John Rennie

OK :-)

Sarabsri mt

6:18 AM

Sir , in these images. The formula that we have

Are these lik value of energy

that we need for the electron to jump

and therefore , then only it gives spectrum

John Rennie

Yes. In a hydrogen atom we label the states 1s, 2s, etc by the principle quantum number that we call n.

Sarabsri mt

Yes sir.

John Rennie

For the 1s n=1, for the 2s and 2p n=2, and so on.

Sarabsri mt

That is right sir

John Rennie

And the energy of the electron in the orbital is E(n) = -E₀/n² where E₀ is a constant.

Sarabsri mt

6:21 AM

Ohk. This is right theory

As well right?

Or not like Bohr Model

John Rennie

Yes. We get these energies by solving an equation called the Schrodinger equation that describes electrons in atoms.

Sarabsri mt

-$E_0$ is $R_H$

@JohnRennie ohk.

John Rennie

@Sarabsrimt Yes.

Sarabsri mt

It is negative because direction of displacement and force is negative

Sonce F* Disp

John Rennie

Most of us remember it as E₀ = 13.6 electron volts.

Sarabsri mt

6:23 AM

n at infinity is 1. Then , it goes back

@JohnRennie K yes

John Rennie

The electron volt is a convenient unit of energy for atoms.

Sarabsri mt

Yes sir. 👍🏻

@JohnRennie Also , you write orbitals here.

It should be orbits right

it is a gas

John Rennie

No.

The 1s, 2s, etc are called orbitals.

Sarabsri mt

Ohk yes

Sir , another doubt .

In uncertainty principle

John Rennie

Atomic orbital

In atomic theory and quantum mechanics, an atomic orbital is a mathematical function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term atomic orbital may also refer to the physical region or space where the electron can be calculated to be present, as predicted by the particular mathematical form of the orbital.Each orbital in an atom is characterized by a unique set of values of the three quantum numbers n, ℓ, and ml, which...

Sarabsri mt

6:26 AM