What is Quantum number: Definition and 83 Discussions

In chemistry and quantum physics, quantum numbers describe values of conserved quantities in the dynamics of a quantum system. Quantum numbers correspond to eigenvalues of operators that commute with the Hamiltonian—quantities that can be known with precision at the same time as the system's energy—and their corresponding eigenspaces. Together, a specification of all of the quantum numbers of a quantum system fully characterize a basis state of the system, and can in principle be measured together.
An important aspect of quantum mechanics is the quantization of many observable quantities of interest. In particular, this leads to quantum numbers that take values in discrete sets of integers or half-integers; although they could approach infinity in some cases. This distinguishes quantum mechanics from classical mechanics where the values that characterize the system such as mass, charge, or momentum, all range continuously. Quantum numbers often describe specifically the energy levels of electrons in atoms, but other possibilities include angular momentum, spin, etc. An important family is flavour quantum numbers – internal quantum numbers which determine the type of a particle and its interactions with other particles through the fundamental forces. Any quantum system can have one or more quantum numbers; it is thus difficult to list all possible quantum numbers.

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  1. L

    Can anyone define magnetic quantum number?

    all it says in the chemistry book is that a magnetic quantum number is the spatial orientation of the orbital ? That doesn't really tell you much. What exactly do they mean by that? also on the web the definitions don't really say much, they seem to have pages and pages of stuff that the...
  2. S

    Parity dependence on the orbital quantum number (l)

    Hi, I know that the angular momentum eigenfunctions in spherical coordinates are spherical harmonics, Ylm ( \theta, \phi ) \propto (-1)mPlm(cos\theta)eim\phi. Applying the parity operator to Ylm ( \theta,\phi ) means that \theta -> \pi - \theta and \phi -> \phi +\pi. This implies that...
  3. L

    Understanding Electron Shells: Defined by Principal Quantum Number

    What would be the best way to define electron shell? I know that it is identified by the principal quantum number, but not sure how to clearly define it.
  4. A

    Orbital angular momentum quantum number

    Why is the s,p,d,.. nomenclature derived for the H atom also valid for many-electron atoms?
  5. P

    Principal Quantum number by size?

    Homework Statement What is the value of the principal quantum number for a hydrogen atom to have a size of one micron?Homework Equations r=(5.3x10-11)(n2) r=1x10-6/2=5x10-7The Attempt at a Solution 5x10-7=(5.3x10-11)(n2) 97.1 = n How is this possible? lol Maybe it's more complicated then I'm...
  6. L

    Angular momentum quantum number and angle

    Homework Statement What are the possible values for the magnetic quantum number ml for an electron whose orbital quantum number is l = 4? What are the allowed values of the angles between L and the zaxis in this case? Homework Equations The Attempt at a Solution Is Ml equal...
  7. C

    Principle Quantum Number - Transition

    Homework Statement Is the following transition allowed? [4,3,0,1/2] -> [4,2,1, -1/2] If so, find the energy involved and whether the photon is absorbed or emitted for the hydrogen atom. Homework Equations Selection rules for allowed transitions: \Deltan = anything \Deltal =\pm1...
  8. S

    Rotational energy levels vs l quantum number

    H2 has a moment of inertia equal to 4.603 x 10-48 kg m2. 1) Calculate its bond length. 2) For the first 3 rotational energy levels, find the a) l quantum number b) ml quantum number c) the degeneracy of each rotational level d) energy eigenvalues e) the magnitude of l Ok so I...
  9. MTd2

    Space time signature as a quantum number and antigravitaion (nothing crank here)

    http://arxiv.org/abs/0909.3456 Antigravitation Sabine Hossenfelder (Submitted on 18 Sep 2009) We discuss why there are no negative gravitational sources in General Relativity and show that it is possible to extend the classical theory such that repulsive gravitational interaction occurs...
  10. W

    Principle Quantum Number Question

    Homework Statement The hydrogen spectrum contains a blue line with a wavelength of 434 nm. Photons of blue light are emitted when hydrogens electron drops from the fifth energy level to a lover energy level. What is the lower energy level? Homework Equations En = 13.6 eV/n^2 E =...
  11. J

    Azimuthal quantum number,l and magnetic quantum number, m

    as in Y^{m}_{l}, what is l and m mean in their spherical coordinate
  12. S

    I really with spin quantum number.

    Hello. I am in class eleventh. I met a class 12th guy telling me that he knew a theoretical proof for showing that the values of spin quantum number are +1/2 and -1/2. If anyone else knows the proof, please tell me...I'm desperate to know.. Any help would be appreciated.
  13. A

    Electronic Structure (magnetic quantum number)

    Homework Statement Describe a possible set of quantum numbers for the 44th electron in mercury. The Attempt at a Solution I can't help but feel a bit embarrassed by some of the questions I ask on this forum. Nevertheless, I am having problems with figuring out what the magnetic...
  14. D

    Spin Quantum Number: Why is it Always + or - 1/2?

    My chemistry teacher gave us a question just to make us search that why is the Spin Quantum Number always + or - 1/2. I tried searching on the net, but i got different answers on different websites. Why exactly is it, why can't it be 1,2,3 or some other number.
  15. Y

    Principal quantum number n, large ones for hydrogen

    hi folks, had a problem I couldn't do, though I made a valiant effort. perhaps you can tell me where I went wrong. Homework Statement All integer values of the principal quantum number n, even very large ones, are allowed in atoms. In practice, it is very hard to excite orbits that...
  16. K

    Quantum number and electronic configuration

    Homework Statement The problem is: find all possible quantum numbers for each electronic configure of carbon. 2. The attempt at a solution I don't quite understand what the question is asking. Does it ask first write down the electronic configuration and write down all quantum number...
  17. U

    Inferring the Principal Quantum Number from a Given Wave Function

    Hi, I am new here. I am a graduate student of department of physics at some university in Korea. If there is any wrong in my english, I will apologize in advance. I am preparing for my qualifying exam that is going to be held on next month. Homework Statement The question is very simple as...
  18. I

    Probability of finding a state with azimuthal orbital quantum number

    STATEMENT: A system is known to be in the normalized state described by the wave function \psi(\theta,\phi)=\frac{1}{\sqrt{30}}(5Y_4^3+Y_6^3-2Y_6^0) What is the probaility of finding the system in a state with azmithual orbital quantum number m=3?WHAT I HAVE: We know that...
  19. L

    Total angular momentum quantum number

    lets say there is an electron configuraiton of 1s^2 2s^2 2p^2 3p^1 I want to find the total angular momentum quantum number, J=L+S considering the n=1 state, there are two electrons, in the s shell which means one is spin 1/2 and the other is spin -1/2 giving a total spin of 0. The s shell...
  20. N

    Understanding Magnetic Quantum Numbers: Demystifying the Concept for Students

    Being a student sometime i confuse about the real concept of magnetic quantum number. Somwhere i perceived when orbit is introduced in external magnetic field then magnetic quantum number.But there is still magnetic field due to electrons as well? I am confused about whole story? Can anyone...
  21. J

    What is the approximate quantum number of the electron?

    [SOLVED] particle in a box Homework Statement An electron moves with a speed of v = 10^{-4}c inside a one-dimensional box of length 48.5nm. The potential is infinite elsewhere. What is the approximate quantum number of the electron? Homework Equations E_{n} =...
  22. E

    Quantum number and wave vector

    Hello! Can you help me a question? -The particle was describeb by 3 quantum number: n,l,m (not consider the spin). -But in Solid books, writer often use wave vector \vec{k} to describe state of particle. That is kx, ky and kz with 3 dimension of coordinate. Then, what relation with 3 quantum...
  23. I

    "Understanding the Spin Quantum Number -1/2 & +1/2

    Homework Statement Why is the spin quantum number either +1/2 or -1/2 Homework Equations N.A. The Attempt at a Solution I am not sure but this is the way i thought of it. Whatevrr quantum numbers i have known of so far: Principal, Azumithal tc. all of them have a diffrence of...
  24. F

    Values of the agular momentum quantum number

    Hello! Why is it the case, that the principle quantum number limits the values of the angular momentum quantum number like l <= n-1 How is it possible to derive this? Thank you for your answers.
  25. T

    Good Quantum Numbers: Helicity & Invariants

    If an operator commutes with the Hamiltonian, then, the eigenvalues are said to be good quantum numbers. For example, the helicity. But then, helicity is not an invariant for a massive particle. I can always go to another Lorentz frame such that the helicity is now reversed. How then, can it be...
  26. G

    Understanding Principal Quantum Numbers for Sulfur and Arsenic Valence Electrons

    Could someone please help me firgure out this homework problem? "What is the principal quantum number of the s and p valence electrons in sulfur and arsenic?"
  27. L

    Valid Quantum Number Sets: Analyzing n, l, and ml Values for Set 1, 2, and 3

    I have a chart and I have to say if any of the sets are not valid: ------------------------ _____n__l__ml Set 1: 6 4 -4 Set 2: 1 0 -1 Set 3: 4 1 1 ----------------------- and my choices are: a) set 1 only b) set 2 only c) set...
  28. L

    Quantum number / orbital question

    For the pairs below, I need to name the orbital they describe... I just am checking that I am on the right track: a) n=5, l=0 >> 5s b) n=3, l=1 >> 3p c) n=4, l=2 >> 4d if those are not correct, can someone lead me in the right direction?
  29. B

    How to prove gluon has this quantum number assignment?

    [URGENT]How to prove gluon has this quantum number assignment? From PDG booklet, for gluon, I^G(J^{PC}) = 0(1^-). My questions are: 1. How to prove its P=-1? 2. Why C parity and therefore G parity are not well-defined for a gluon? Is it because gluon have nothing to do with...
  30. H

    How does increasing distance affect potential energy in an atom?

    The larger n, the longer the orbitals, the higher the energy level, and the higher the speed of electrons?
  31. Amith2006

    Why is Spin Quantum Number Given 1/2?

    Why is the spin quantum number given a value 1/2? Why not any other value, say +1 for clockwise spin and -1 for anticlockwise spin instead of +1/2 for clockwise spin and -1/2 for anticlockwise spin ?
  32. U

    Calculating Quantum Number n for a Mass Moving in an Infinite Square Well

    a mass of 10^-6 grams is moving at a speed of 0.1 cm/s in a box 1 cm in length. Treating this as a 1-D infinite square well, i am to calculate the quantum number n: i was wondering if I am setting this up correct: \frac{1}{2} * 10^{-6 }g * 0.1 cm/s = \frac{n^2 \pi^2 \hbar ^2}{2*10^{-6 }g *...
  33. A

    Is the Principal Quantum Number n the Same as Planck's Proposed Quantization?

    was the principal quantum number proposed by Planck? i remember that Planck proposed quantization, n, but is that the same thing as the principal quantum number n? the principal quantum number represents the quantization of energy, right?
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