What characteristic is given by the angular momentum quantum number?

1 Answer
Nov 7, 2016

The angular momentum quantum number #l# describes the shape of an orbital. It corresponds to each orbital type, i.e. #(0,1,2,3, . . . , n-1) = (s, p, d, f, g, h, . . . )#.

Note that:

  • #l_max = n - 1#
  • #l = 0, 1, 2, 3, . . . , n - 1#
  • #2l + 1# is the number of orbitals in a given #l# subshell.
  • #l# is the number of angular nodes in an orbital.

So two examples:

http://chem.libretexts.org/

#1s# orbital:

  • #bb(n = 1)# for the principal quantum number (read it off the orbital name).

Thus, #l_max = bb(l = 0)#. This also means there is no angular node in the #1s# orbital.

  • #2l + 1 = 2(0) + 1 = bb(1)#. Thus, there is only one #1s# orbital.

That is also determined by realizing that for the magnetic quantum number, #m_l = {0}# due to #l = 0#. i.e. the only #1s# orbital there is has #l = 0#.

#2s, 2p# orbital(s):

  • #bb(n = 2)# for the principal quantum number (read it off the orbital name).

Thus, #bb(l = 0, 1)#, and #l_max = 1#. This also means there is no angular node in the #2s# orbital, but #bb(1)# angular node in each #2p# orbital.

  • For the #2s# orbital(s), #2l + 1 = 2(0) + 1 = bb(1)#. Thus, there is only one #2s# orbital.

That is also determined by realizing that for the magnetic quantum number, #m_l = {0}# due to #l = 0#. i.e. the only #1s# orbital there is has #l = 0#.

  • For the #2p# orbital(s), #2l + 1 = 2(1) + 1 = bb(3)#. Thus, there are three #2p# orbitals.

That is also determined by realizing that for the magnetic quantum number, #m_l = {-1, 0 +1}# due to #l = 1#. i.e. each #2p# orbital uniquely corresponds to either #l = -1#, #0#, or #+1#. As there are three #m_l# values, there are three #2p# orbitals.