Is it true that for a value of nn (n-principal quantum number), the value of m_lml (m_lml-magnetic quantum number) is equal to n^2n2? If it is true, can you please explain this to me? Thanks.

1 Answer
Jul 6, 2015

The actual value, no. The number of values, yes.

Explanation:

The relationship between the principal quantum number, nn, and the magnetic quantum number, m_lml, actually goes through the angular momentum quantum number, ll.

![https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/introduction-to-quantum-theory-7](useruploads.socratic.org)

The angular momentum quantum number can take any value that ranges from 00 to n-1n1

l = 0, 1, 2, ... , (n-1)

The magnetic quantum number can take any value that ranges from -l to l

m_l = -l, ... , -1, 0, 1, ... , l

If you take into account the possible values of l, the magnetic quantum number can thus have values that range from

m_l = -(n-1), ..., -1, 0, 1, ..., (n-1)

So, for example, if n=2, m_l can be equal to

m_l = 0 -> for l=0

and

m_l = {-1, 0, 1} -> for l=1

As you can see, the individual values of m_l don't even come close to the value of n^2.

However, the total number of values m_l can take, if you take into account the values of l, is indeed equal to n^2.

The magnetic quantum number actually tells you how many orbitals a subshell has. In the above example, if n=2, you get

n=2, l=0, m_l = 0 -> one 2s-orbital;

{:(n=2, l=1, m_l = -1->2p_x), (n=2, l=1, m_l = 0->2p_y), (n=2, l=1, m_l = 1->2p_z) :}} -> three 3p-orbitals.

This means that the second energy level has a total of two subshells, the 2s-subshell and the 2p-subshell.

The number of orbitals each subshell contains is given by m_l. The 2s-subshell contains one orbital, since you only have one possible value for m_l.

The 2p-subshell contains 3 orbitals, each denoted by a different value of m_l.

The total number of orbitals in the second energy level is 4, which is equal to n^2.

If you try this with n=3, you'll find that you get a total number of 9 orbitals

  • one 3s-orbital;
  • three 3p-orbitals;
  • five 3d-orbitals.