Bohr's Postulates (1 Viewer)

[shazzam]

Several issues needing urgent addressal:
1. Could someone kindly explain in simple terms what is the meaning of Bohr's 2nd postulate (something to do with angular momentum involving a formula).

2. Could that same person or anyone else please explain what exactly is counted as the 2nd postulate and what is the 3rd postulate? Currently I only feel confident about the 1st postulate that describes electrons being in certain orbits which they cannot leave unless they absorb/emit a certain quanta of energy. (right?).

Your generosity is much appreciated.

 

[leginag]

umm...i'm under the impression the three postulates are

1) Electrons in an atom exist in stable, circular orbits. Electrons in stable orbits do not emit radiation

2) When an electron fallls from a higher energy level to a lower energy level it emits energy that is quantised by the plank relationship

E^1-E^2=deltaE=hf. where E^1= initial state and E^2 =final state


3) An electron in a stationary state has Angular momentum(mvr) which is quantised and can only take values of

nh/2pi where n is the principle quantum number


If i'm wrong or anyone has any more details...i'd appreciate if if someone would nicely correct me

____________
Wolf^^

 

[acmilan]

leginag you're correct and it is important to remember the numbers for each because a question once arose to state his third postulate and if u dont learn the order you would be screwed for that question

 

[leginag]

could someone please explain the third postulate??? i mean its all great knowing the actual postulate...but i haf no idea wt it means exactly (A)

__________
Wolf^^

 

[angelduck]

Is it also important to know what each of the postulates explained about earlier models??

wait, scratch that, i dont think that made any sense at all.

Um, with the third postulate, i know that it is based on PLanck's formulae/ideas and that it also explains the emission/absorption of specific frequencies.

Um, also, i have like 5 postulates, because one of the books i read did, are there only the three?? Did the book just make up the other ones??

They Are (this comes form my summary, so ignore the extra bits to the postulates):
(1) electrons can occupy only certain stationary states - explains the atomic emission spectra

(2) electrons orbit a positive nucleus - explains rutherford's experimental results

(3) electrons do not radiate EM radiation - accounts for stability

(4) E=hf - explains the emission/absorption of specific frequencies

(5) electrostatic forces provide centripetal force hypothesised by Rutherford.

Um, please explain why i have 5, doi i have extra ones?? Are they all right, im soo confused!

 

[Xayma]

The first two are the postulates (of the second post), the third one is sometimes considered one sometimes not.

 

[shazzam]

umm...i'm under the impression the three postulates are

1) Electrons in an atom exist in stable, circular orbits. Electrons in stable orbits do not emit radiation

2) When an electron fallls from a higher energy level to a lower energy level it emits energy that is quantised by the plank relationship

E^1-E^2=deltaE=hf. where E^1= initial state and E^2 =final state


3) An electron in a stationary state has Angular momentum(mvr) which is quantised and can only take values of

nh/2pi where n is the principle quantum number

____________
Wolf^^

I think that this is a correct and succinct way of expressing it. Yes there are definitely 3 postulates, at least in most of the more common textbooks.

I'm thinking that the 3rd postulate says that in each shell the electrons can only spin at a certain speed, or more correctly momentum because their motion carries energy, which is a quantised value i.e. they cannot suddenly go faster or slower, and also the movement is different for electrons in different shells. I don't know, I can see it but it's hard to describe...

 

[angelduck]

Thank you! I think ill just deal with the three mentioned earlier, 5 is too much.

Um, with the spin, doesn't that just edscribe if it is spin up or spin down (Pauli's 4th quantum number) From focus 2??

 

[joshhopp]

the importance of the thrid postulate was that it explained why electrons dont emit EM radiation as classical physics sugested they should. it didnt really explain it though, it was an 'ad hoc' assumption: de Broglie explained it by comparing the orbit to the creation of a standing wave

 

[:: ck ::]

angular momentum one is referred to the quantisation condition

 

[Tommy_Lamp]

i dont believe it is required to understand his postulates, but merely to state what they are

 

[Constip8edSkunk]

i dont believe it is required to understand his postulates, but merely to state what they are

lol ...i think thats basically the outline of the whole physics course

 

[redslert]

it's always nice to know the meaning behind them because it is easier to remember

 

[Tommy_Lamp]

i dont agree when it comes to his postulates, i prefer not to have to learnn extra things. IMO its easier to just memorise them