January 26, 2021, 09:06:48 PM
Forum Rules: Read This Before Posting


Topic: Chemistry energy help ?  (Read 7074 times)

0 Members and 1 Guest are viewing this topic.

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Chemistry energy help ?
« on: October 03, 2014, 10:14:58 AM »
Among the following electrons, which has highest energy?

a. n = 3, l = 2, m = 0, s = + 1/2
b. n = 4, l = 0. m= 0 , s = - 1/s

answer is A.

but i want to know that how to get this answer help please?

Offline Corribus

  • Chemist
  • Sr. Member
  • *
  • Posts: 3025
  • Mole Snacks: +458/-22
  • Gender: Male
  • A lover of spectroscopy and chocolate.
Re: Chemistry energy help ?
« Reply #1 on: October 03, 2014, 10:42:09 AM »
The answer is not A based on the information provided. The answer is "it depends". In a hydrogenic atom, the energy depends only on the quantum number n and is proportional to the negative of the inverse of n2. B is therefore the appropriate answer for a hydrogenic atom. For a multi-electronic atom, this changes because the l quantum number impacts energy (due to penetration and shielding effects). Here we're basically being asked what fills first: the 3d or 4s orbital when putting multiple electrons into hydrogenic orbitals. The 3d is usually filled first, which would indicate an answer of A for a large multielectronic atom. Also, we usually ignore electron spin in a first approximation (in absence of magnetic field), but you can also take spin-orbit coupling into account if you wish, which can complicate things further.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #2 on: October 03, 2014, 11:10:20 AM »
The answer is not A based on the information provided. The answer is "it depends". In a hydrogenic atom, the energy depends only on the quantum number n and is proportional to the negative of the inverse of n2. B is therefore the appropriate answer for a hydrogenic atom. For a multi-electronic atom, this changes because the l quantum number impacts energy (due to penetration and shielding effects). Here we're basically being asked what fills first: the 3d or 4s orbital when putting multiple electrons into hydrogenic orbitals. The 3d is usually filled first, which would indicate an answer of A for a large multielectronic atom. Also, we usually ignore electron spin in a first approximation (in absence of magnetic field), but you can also take spin-orbit coupling into account if you wish, which can complicate things further.

My solution :

As we know that L shell is closest to nucleus and after that there is M shell and then N shell , In this way , if we notice the answer A , we can see that there are 2 electrons in it and is full, where as the second option has 4 electrons in N shell but we know that N shell is far from nucleus whereas L shell with 2 electrons is closer to the nucleus hence the answer is A. n=3, l = 2 , m = 0 = +1/2 - independent of spin, dependent on orbitals/energy shells.

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1838
  • Mole Snacks: +257/-12
Re: Chemistry energy help ?
« Reply #3 on: October 04, 2014, 02:39:00 PM »
The L shell is not closest to the nucleus, the K shell is.
A full L shell has 8 electrons, not 2.
n=3 is the M shell, not L.
Who said there were 4 electrons in the N shell? It's not specified anywhere.
Have you taken on board what Corribus said?

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #4 on: October 04, 2014, 03:03:37 PM »
Sir, what I am telling is different , I got what above man said .

Listen sir,

K shell is closest one but when it comes to N shell and L shell , then L is more closest to the nucleus, thats what i was saying , in this way i opted this answer.

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1838
  • Mole Snacks: +257/-12
Re: Chemistry energy help ?
« Reply #5 on: October 04, 2014, 03:38:21 PM »
OK, I thought you were confusing L with K, because you said L was full with 2 electrons, which is not true.
In any case, answer A refers to the M shell, not the L.

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #6 on: October 04, 2014, 04:54:32 PM »
Sir, This is confusing me here , that if M=0 in both answers , then why answer .A is correct , M=0 in both , it means answer is choosen on then basis of L shell?

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1838
  • Mole Snacks: +257/-12
Re: Chemistry energy help ?
« Reply #7 on: October 05, 2014, 01:51:21 PM »
n, l and m are not the numbers of electrons in the N, M and L shells, but the quantum numbers describing an electron
The principal quantum number n=1 is K shell, 2 is L, 3 is M etc.
The orbital quantum number l = 0 for an s orbital, 1 for p, 2 for d etc.
m or ml gives the quantisation of the angular momentum along the x axis, e.g. for l = 1, ml = +1, 0 or -1.
ms (not s) is the spin quantisation, ±1/2
Are you familiar with these concepts?

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Re: Chemistry energy help ?
« Reply #8 on: October 05, 2014, 02:04:24 PM »
N ,m , l , s are not shells..!! These are quantum numbers...!!
Are you from india....??
If you are from indian CBSE board then did you read atomic structure from NCERT ...??

Its not about from which part of the world you belong the main thing is that did you read about atomic structure....??

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #9 on: October 06, 2014, 07:52:12 AM »
n, l and m are not the numbers of electrons in the N, M and L shells, but the quantum numbers describing an electron
The principal quantum number n=1 is K shell, 2 is L, 3 is M etc.
The orbital quantum number l = 0 for an s orbital, 1 for p, 2 for d etc.
m or ml gives the quantisation of the angular momentum along the x axis, e.g. for l = 1, ml = +1, 0 or -1.
ms (not s) is the spin quantisation, ±1/2
Are you familiar with these concepts?

Sir, i have just passed high school , and now preparing for mcat only 15 days are remaining in my mcat test, so i am familar with these concepts , i have went into deep study of azimuthal quantum number , pauli excl. prin. etc and all that magnetic quantum no .  but the questions which they give in our mcat test are mroe out of syllabus u can say, so if we keep all these discussions on one side sir, please tell me and guide me that if such question come in exams, in theoritical form what will be its answer? how will i answer such question?

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #10 on: October 06, 2014, 08:01:40 AM »
N ,m , l , s are not shells..!! These are quantum numbers...!!
Are you from india....??
If you are from indian CBSE board then did you read atomic structure from NCERT ...??

Its not about from which part of the world you belong the main thing is that did you read about atomic structure....??

I am from Pakistan , we have same study structure as india .
sorry sir, i was wrong my mistake, i dont know why i choosed science , i am such a dumb person on this earth, btw, the mistake i made was that if u guys clearly see the answer A and B u will come to know that it is written n =3 , l=2 ,m=0 , now what i thought was that this "l" is actually L of energy level shell , but i was wrong its capital L for energy shell , the small "l" is for magnetic quantum number which decides the orientation of orbitals in the space, in applied magnetic field .

I am still getting confused , please tell me that the questino aska which electrons has highest energy then how should i solve it or choose answer. I have lost all hopes believe me , 1 week has been passed i cant figure out even the basic of subject how I am going to be a doctor , I should leave science and join painting class , i dont deserve it .

so , i want to ask that the difference between both answers is in l=0 and l=2 . what is such thing which make us select l=2 as a correct answer . help  ???

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #11 on: October 06, 2014, 08:08:14 AM »
The L shell is not closest to the nucleus, the K shell is.
A full L shell has 8 electrons, not 2.
n=3 is the M shell, not L.
Who said there were 4 electrons in the N shell? It's not specified anywhere.
Have you taken on board what Corribus said?

help sir, u said that if n=3 is the m shell , plz demonstrate how?

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #12 on: October 06, 2014, 08:21:04 AM »
Sir, see my work.

n=1=K
n=2=L
n=3=M √
n=4=N

now if n = 3 = m , then what is the function of l and m in the question, this thing is out of my reach?

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1838
  • Mole Snacks: +257/-12
Re: Chemistry energy help ?
« Reply #13 on: October 06, 2014, 08:25:47 AM »
The quantum number n denotes the successive electron shells, so n=1 is K, n=2 is L, n=3 is M, n=4 is N and so on.
Corribus has already given the best answer to this question, I don't see what else I can say.
The question is probably alluding to the fact that e.g. for potassium the electron configuration is 1s22s22p63s23p64s1, i.e. the outermost electron goes in 4s (answer B) rather than 3d (answer A) as might be expected. In this case then, A is the higher energy. But the relative energy of these orbitals varies with atomic number.

Offline Shahab Mirza

  • Regular Member
  • ***
  • Posts: 54
  • Mole Snacks: +0/-0
Re: Chemistry energy help ?
« Reply #14 on: October 06, 2014, 08:28:30 AM »
Thanks for your , fast reply  and help , but I gave up . i am not getting it , so after two days i will again go through the chapter of atomic structure and then tell you guys that if i understood or not, thanks

Sponsored Links